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• Reusable VS clean code - where's the balance?

  - by Radek Šimko

  Let's say I have a data model for a blog posts and have two use-cases of that model - getting all blogposts and getting only blogposts which were written by specific author. There are basically two ways how I can realize that. 1st model class Articles { public function getPosts() { return $this->connection->find() ->sort(array('creation_time' => -1)); } public function getPostsByAuthor( $authorUid ) { return $this->connection->find(array('author_uid' => $authorUid)) ->sort(array('creation_time' => -1)); } } 1st usage (presenter/controller) if ( $GET['author_uid'] ) { $posts = $articles->getPostsByAuthor($GET['author_uid']); } else { $posts = $articles->getPosts(); } 2nd one class Articles { public function getPosts( $authorUid = NULL ) { $query = array(); if( $authorUid !== NULL ) { $query = array('author_uid' => $authorUid); } return $this->connection->find($query) ->sort(array('creation_time' => -1)); } } 2nd usage (presenter/controller) $posts = $articles->getPosts( $_GET['author_uid'] ); To sum up (dis)advantages: 1) cleaner code 2) more reusable code Which one do you think is better and why? Is there any kind of compromise between those two?

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• Looking into Enum Support in Entity Framework 5.0 Code First

  - by nikolaosk

  In this post I will show you with a hands-on demo the enum support that is available in Visual Studio 2012, .Net Framework 4.5 and Entity Framework 5.0. You can have a look at this post to learn about the support of multilple diagrams per model that exists in Entity Framework 5.0. We will demonstrate this with a step by step example. I will use Visual Studio 2012 Ultimate. You can also use Visual Studio 2012 Express Edition. Before I move on to the actual demo I must say that in EF 5.0 an enumeration can have the following types. Byte Int16 Int32 Int64 Sbyte Obviously I cannot go into much detail on what EF is and what it does. I will give again a short introduction.The .Net framework provides support for Object Relational Mapping through EF. So EF is a an ORM tool and it is now the main data access technology that microsoft works on. I use it quite extensively in my projects. Through EF we have many things out of the box provided for us. We have the automatic generation of SQL code.It maps relational data to strongly types objects.All the changes made to the objects in the memory are persisted in a transactional way back to the data store. You can find in this post an example on how to use the Entity Framework to retrieve data from an SQL Server Database using the "Database/Schema First" approach. In this approach we make all the changes at the database level and then we update the model with those changes. In this post you can see an example on how to use the "Model First" approach when working with ASP.Net and the Entity Framework. This model was firstly introduced in EF version 4.0 and we could start with a blank model and then create a database from that model.When we made changes to the model , we could recreate the database from the new model. You can search in my blog, because I have posted many posts regarding ASP.Net and EF. I assume you have a working knowledge of C# and know a few things about EF. The Code First approach is the more code-centric than the other two. Basically we write POCO classes and then we persist to a database using something called DBContext. Code First relies on DbContext. We create 2,3 classes (e.g Person,Product) with properties and then these classes interact with the DbContext class. We can create a new database based upon our POCOS classes and have tables generated from those classes.We do not have an .edmx file in this approach.By using this approach we can write much easier unit tests. DbContext is a new context class and is smaller,lightweight wrapper for the main context class which is ObjectContext (Schema First and Model First). Let's begin building our sample application. 1) Launch Visual Studio. Create an ASP.Net Empty Web application. Choose an appropriate name for your application. 2) Add a web form, default.aspx page to the application. 3) Now we need to make sure the Entity Framework is included in our project. Go to Solution Explorer, right-click on the project name.Then select Manage NuGet Packages...In the Manage NuGet Packages dialog, select the Online tab and choose the EntityFramework package.Finally click Install. Have a look at the picture below   4) Create a new folder. Name it CodeFirst . 5) Add a new item in your application, a class file. Name it Footballer.cs. This is going to be a simple POCO class.Place it in the CodeFirst folder. The code follows public class Footballer { public int FootballerID { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public double Weight { get; set; } public double Height { get; set; } public DateTime JoinedTheClub { get; set; } public int Age { get; set; } public List<Training> Trainings { get; set; } public FootballPositions Positions { get; set; } }    Now I am going to define my enum values in the same class file, Footballer.cs    public enum FootballPositions    {        Defender,        Midfielder,        Striker    } 6) Now we need to create the Training class. Add a new class to your application and place it in the CodeFirst folder.The code for the class follows.     public class Training     {         public int TrainingID { get; set; }         public int TrainingDuration { get; set; }         public string TrainingLocation { get; set; }     }   7) Then we need to create a context class that inherits from DbContext.Add a new class to the CodeFirst folder.Name it FootballerDBContext.Now that we have the entity classes created, we must let the model know.I will have to use the DbSet<T> property.The code for this class follows       public class FootballerDBContext:DbContext     {         public DbSet<Footballer> Footballers { get; set; }         public DbSet<Training> Trainings { get; set; }     } Do not forget to add  (using System.Data.Entity;) in the beginning of the class file 8) We must take care of the connection string. It is very easy to create one in the web.config.It does not matter that we do not have a database yet.When we run the DbContext and query against it,it will use a connection string in the web.config and will create the database based on the classes. In my case the connection string inside the web.config, looks like this      <connectionStrings>    <add name="CodeFirstDBContext"  connectionString="server=.\SqlExpress;integrated security=true;"  providerName="System.Data.SqlClient"/>                       </connectionStrings>   9) Now it is time to create Linq to Entities queries to retrieve data from the database . Add a new class to your application in the CodeFirst folder.Name the file DALfootballer.cs We will create a simple public method to retrieve the footballers. The code for the class follows public class DALfootballer     {         FootballerDBContext ctx = new FootballerDBContext();         public List<Footballer> GetFootballers()         {             var query = from player in ctx.Footballers where player.FirstName=="Jamie" select player;             return query.ToList();         }     }   10) Place a GridView control on the Default.aspx page and leave the default name.Add an ObjectDataSource control on the Default.aspx page and leave the default name. Set the DatasourceID property of the GridView control to the ID of the ObjectDataSource control.(DataSourceID="ObjectDataSource1" ). Let's configure the ObjectDataSource control. Click on the smart tag item of the ObjectDataSource control and select Configure Data Source. In the Wizzard that pops up select the DALFootballer class and then in the next step choose the GetFootballers() method.Click Finish to complete the steps of the wizzard. Build your application.  11)  Let's create an Insert method in order to insert data into the tables. I will create an Insert() method and for simplicity reasons I will place it in the Default.aspx.cs file. private void Insert()        {            var footballers = new List<Footballer>            {                new Footballer {                                 FirstName = "Steven",LastName="Gerrard", Height=1.85, Weight=85,Age=32, JoinedTheClub=DateTime.Parse("12/12/1999"),Positions=FootballPositions.Midfielder,                Trainings = new List<Training>                             {                                     new Training {TrainingDuration = 3, TrainingLocation="MelWood"},                    new Training {TrainingDuration = 2, TrainingLocation="Anfield"},                    new Training {TrainingDuration = 2, TrainingLocation="MelWood"},                }                            },                            new Footballer {                                  FirstName = "Jamie",LastName="Garragher", Height=1.89, Weight=89,Age=34, JoinedTheClub=DateTime.Parse("12/02/2000"),Positions=FootballPositions.Defender,                Trainings = new List<Training>                                             {                                 new Training {TrainingDuration = 3, TrainingLocation="MelWood"},                new Training {TrainingDuration = 5, TrainingLocation="Anfield"},                new Training {TrainingDuration = 6, TrainingLocation="Anfield"},                }                           }                    };            footballers.ForEach(foot => ctx.Footballers.Add(foot));            ctx.SaveChanges();        }   12) In the Page_Load() event handling routine I called the Insert() method.        protected void Page_Load(object sender, EventArgs e)        {                   Insert();                }  13) Run your application and you will see that the following result,hopefully. You can see clearly that the data is returned along with the enum value.  14) You must have also a look at the database.Launch SSMS and see the database and its objects (data) created from EF Code First.Have a look at the picture below. Hopefully now you have seen the support that exists in EF 5.0 for enums.Hope it helps !!!

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• Looking into Entity Framework Code First Migrations

  - by nikolaosk

  In this post I will introduce you to Code First Migrations, an Entity Framework feature introduced in version 4.3 back in February of 2012.I have extensively covered Entity Framework in this blog. Please find my other Entity Framework posts here .   Before the addition of Code First Migrations (4.1,4.2 versions), Code First database initialisation meant that Code First would create the database if it does not exist (the default behaviour - CreateDatabaseIfNotExists). The other pattern we could use is DropCreateDatabaseIfModelChanges which means that Entity Framework, will drop the database if it realises that model has changes since the last time it created the database.The final pattern is DropCreateDatabaseAlways which means that Code First will recreate the database every time one runs the application.That is of course fine for the development database but totally unacceptable and catastrophic when you have a production database. We cannot lose our data because of the work that Code First works.Migrations solve this problem.With migrations we can modify the database without completely dropping it.We can modify the database schema to reflect the changes to the model without losing data.In version EF 5.0 migrations are fully included and supported. I will demonstrate migrations with a hands-on example.Let me say a few words first about Entity Framework first. The .Net framework provides support for Object Relational Mappingthrough EF. So EF is a an ORM tool and it is now the main data access technology that microsoft works on. I use it quite extensively in my projects. Through EF we have many things out of the box provided for us. We have the automatic generation of SQL code.It maps relational data to strongly types objects.All the changes made to the objects in the memory are persisted in a transactional way back to the data store. You can find in this post an example on how to use the Entity Framework to retrieve data from an SQL Server Database using the "Database/Schema First" approach.In this approach we make all the changes at the database level and then we update the model with those changes. In this post you can see an example on how to use the "Model First" approach when working with ASP.Net and the Entity Framework.This model was firstly introduced in EF version 4.0 and we could start with a blank model and then create a database from that model.When we made changes to the model , we could recreate the database from the new model. The Code First approach is the more code-centric than the other two. Basically we write POCO classes and then we persist to a database using something called DBContext.Code First relies on DbContext. We create 2,3 classes (e.g Person,Product) with properties and then these classes interact with the DbContext class we can create a new database based upon our POCOS classes and have tables generated from those classes.We do not have an .edmx file in this approach.By using this approach we can write much easier unit tests.DbContext is a new context class and is smaller,lightweight wrapper for the main context class which is ObjectContext (Schema First and Model First).Let's move on to our hands-on example.I have installed VS 2012 Ultimate edition in my Windows 8 machine. 1)  Create an empty asp.net web application. Give your application a suitable name. Choose C# as the development language2) Add a new web form item in your application. Leave the default name.3) Create a new folder. Name it CodeFirst .4) Add a new item in your application, a class file. Name it Footballer.cs. This is going to be a simple POCO class.Place this class file in the CodeFirst folder.The code follows    public class Footballer     {         public int FootballerID { get; set; }         public string FirstName { get; set; }         public string LastName { get; set; }         public double Weight { get; set; }         public double Height { get; set; }              }5) We will have to add EF 5.0 to our project. Right-click on the project in the Solution Explorer and select Manage NuGet Packages... for it.In the window that will pop up search for Entity Framework and install it.Have a look at the picture below   If you want to find out if indeed EF version is 5.0 version is installed have a look at the References. Have a look at the picture below to see what you will see if you have installed everything correctly.Have a look at the picture below 6) Then we need to create a context class that inherits from DbContext.Add a new class to the CodeFirst folder.Name it FootballerDBContext.Now that we have the entity classes created, we must let the model know.I will have to use the DbSet<T> property.The code for this class follows     public class FootballerDBContext:DbContext     {         public DbSet<Footballer> Footballers { get; set; }             }    Do not forget to add  (using System.Data.Entity;) in the beginning of the class file 7) We must take care of the connection string. It is very easy to create one in the web.config.It does not matter that we do not have a database yet.When we run the DbContext and query against it , it will use a connection string in the web.config and will create the database based on the classes.I will use the name "FootballTraining" for the database.In my case the connection string inside the web.config, looks like this    <connectionStrings>    <add name="CodeFirstDBContext" connectionString="server=.;integrated security=true; database=FootballTraining" providerName="System.Data.SqlClient"/>                       </connectionStrings>8) Now it is time to create Linq to Entities queries to retrieve data from the database . Add a new class to your application in the CodeFirst folder.Name the file DALfootballer.csWe will create a simple public method to retrieve the footballers. The code for the class followspublic class DALfootballer     {         FootballerDBContext ctx = new FootballerDBContext();         public List<Footballer> GetFootballers()         {             var query = from player in ctx.Footballers select player;             return query.ToList();         }     } 9) Place a GridView control on the Default.aspx page and leave the default name.Add an ObjectDataSource control on the Default.aspx page and leave the default name. Set the DatasourceID property of the GridView control to the ID of the ObjectDataSource control.(DataSourceID="ObjectDataSource1" ). Let's configure the ObjectDataSource control. Click on the smart tag item of the ObjectDataSource control and select Configure Data Source. In the Wizzard that pops up select the DALFootballer class and then in the next step choose the GetFootballers() method.Click Finish to complete the steps of the wizzard.Build and Run your application.  10) Obviously you will not see any records coming back from your database, because we have not inserted anything. The database is created, though.Have a look at the picture below.  11) Now let's change the POCO class. Let's add a new property to the Footballer.cs class.        public int Age { get; set; } Build and run your application again. You will receive an error. Have a look at the picture below 12) That was to be expected.EF Code First Migrations is not activated by default. We have to activate them manually and configure them according to your needs. We will open the Package Manager Console from the Tools menu within Visual Studio 2012.Then we will activate the EF Code First Migration Features by writing the command “Enable-Migrations”.  Have a look at the picture below. This adds a new folder Migrations in our project. A new auto-generated class Configuration.cs is created.Another class is also created [CURRENTDATE]_InitialCreate.cs and added to our project.The Configuration.cs  is shown in the picture below. The [CURRENTDATE]_InitialCreate.cs is shown in the picture below  13) ??w we are ready to migrate the changes in the database. We need to run the Add-Migration Age command in Package Manager ConsoleAdd-Migration will scaffold the next migration based on changes you have made to your model since the last migration was created.In the Migrations folder, the file 201211201231066_Age.cs is created.Have a look at the picture below to see the newly generated file and its contents. Now we can run the Update-Database command in Package Manager Console .See the picture above.Code First Migrations will compare the migrations in our Migrations folder with the ones that have been applied to the database. It will see that the Age migration needs to be applied, and run it.The EFMigrations.CodeFirst.FootballeDBContext database is now updated to include the Age column in the Footballers table.Build and run your application.Everything will work fine now.Have a look at the picture below to see the migrations applied to our table. 14) We may want it to automatically upgrade the database (by applying any pending migrations) when the application launches.Let's add another property to our Poco class.          public string TShirtNo { get; set; }We want this change to migrate automatically to the database.We go to the Configuration.cs we enable automatic migrations.     public Configuration()        {            AutomaticMigrationsEnabled = true;        } In the Page_Load event handling routine we have to register the MigrateDatabaseToLatestVersion database initializer. A database initializer simply contains some logic that is used to make sure the database is setup correctly.   protected void Page_Load(object sender, EventArgs e)        {            Database.SetInitializer(new MigrateDatabaseToLatestVersion<FootballerDBContext, Configuration>());        } Build and run your application. It will work fine. Have a look at the picture below to see the migrations applied to our table in the database. Hope it helps!!!  

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• Announcing Entity Framework Code-First (CTP5 release)

  - by ScottGu

  This week the data team released the CTP5 build of the new Entity Framework Code-First library.  EF Code-First enables a pretty sweet code-centric development workflow for working with data.  It enables you to: Develop without ever having to open a designer or define an XML mapping file Define model objects by simply writing “plain old classes” with no base classes required Use a “convention over configuration” approach that enables database persistence without explicitly configuring anything Optionally override the convention-based persistence and use a fluent code API to fully customize the persistence mapping I’m a big fan of the EF Code-First approach, and wrote several blog posts about it this summer: Code-First Development with Entity Framework 4 (July 16th) EF Code-First: Custom Database Schema Mapping (July 23rd) Using EF Code-First with an Existing Database (August 3rd) Today’s new CTP5 release delivers several nice improvements over the CTP4 build, and will be the last preview build of Code First before the final release of it.  We will ship the final EF Code First release in the first quarter of next year (Q1 of 2011).  It works with all .NET application types (including both ASP.NET Web Forms and ASP.NET MVC projects). Installing EF Code First You can install and use EF Code First CTP5 using one of two ways: Approach 1) By downloading and running a setup program.  Once installed you can reference the EntityFramework.dll assembly it provides within your projects.      or: Approach 2) By using the NuGet Package Manager within Visual Studio to download and install EF Code First within a project.  To do this, simply bring up the NuGet Package Manager Console within Visual Studio (View->Other Windows->Package Manager Console) and type “Install-Package EFCodeFirst”: Typing “Install-Package EFCodeFirst” within the Package Manager Console will cause NuGet to download the EF Code First package, and add it to your current project: Doing this will automatically add a reference to the EntityFramework.dll assembly to your project:   NuGet enables you to have EF Code First setup and ready to use within seconds.  When the final release of EF Code First ships you’ll also be able to just type “Update-Package EFCodeFirst” to update your existing projects to use the final release. EF Code First Assembly and Namespace The CTP5 release of EF Code First has an updated assembly name, and new .NET namespace: Assembly Name: EntityFramework.dll Namespace: System.Data.Entity These names match what we plan to use for the final release of the library. Nice New CTP5 Improvements The new CTP5 release of EF Code First contains a bunch of nice improvements and refinements. Some of the highlights include: Better support for Existing Databases Built-in Model-Level Validation and DataAnnotation Support Fluent API Improvements Pluggable Conventions Support New Change Tracking API Improved Concurrency Conflict Resolution Raw SQL Query/Command Support The rest of this blog post contains some more details about a few of the above changes. Better Support for Existing Databases EF Code First makes it really easy to create model layers that work against existing databases.  CTP5 includes some refinements that further streamline the developer workflow for this scenario. Below are the steps to use EF Code First to create a model layer for the Northwind sample database: Step 1: Create Model Classes and a DbContext class Below is all of the code necessary to implement a simple model layer using EF Code First that goes against the Northwind database: EF Code First enables you to use “POCO” – Plain Old CLR Objects – to represent entities within a database.  This means that you do not need to derive model classes from a base class, nor implement any interfaces or data persistence attributes on them.  This enables the model classes to be kept clean, easily testable, and “persistence ignorant”.  The Product and Category classes above are examples of POCO model classes. EF Code First enables you to easily connect your POCO model classes to a database by creating a “DbContext” class that exposes public properties that map to the tables within a database.  The Northwind class above illustrates how this can be done.  It is mapping our Product and Category classes to the “Products” and “Categories” tables within the database.  The properties within the Product and Category classes in turn map to the columns within the Products and Categories tables – and each instance of a Product/Category object maps to a row within the tables. The above code is all of the code required to create our model and data access layer!  Previous CTPs of EF Code First required an additional step to work against existing databases (a call to Database.Initializer<Northwind>(null) to tell EF Code First to not create the database) – this step is no longer required with the CTP5 release.  Step 2: Configure the Database Connection String We’ve written all of the code we need to write to define our model layer.  Our last step before we use it will be to setup a connection-string that connects it with our database.  To do this we’ll add a “Northwind” connection-string to our web.config file (or App.Config for client apps) like so:   <connectionStrings>          <add name="Northwind"          connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\northwind.mdf;User Instance=true"          providerName="System.Data.SqlClient" />   </connectionStrings> EF “code first” uses a convention where DbContext classes by default look for a connection-string that has the same name as the context class.  Because our DbContext class is called “Northwind” it by default looks for a “Northwind” connection-string to use.  Above our Northwind connection-string is configured to use a local SQL Express database (stored within the \App_Data directory of our project).  You can alternatively point it at a remote SQL Server. Step 3: Using our Northwind Model Layer We can now easily query and update our database using the strongly-typed model layer we just built with EF Code First. The code example below demonstrates how to use LINQ to query for products within a specific product category.  This query returns back a sequence of strongly-typed Product objects that match the search criteria: The code example below demonstrates how we can retrieve a specific Product object, update two of its properties, and then save the changes back to the database: EF Code First handles all of the change-tracking and data persistence work for us, and allows us to focus on our application and business logic as opposed to having to worry about data access plumbing. Built-in Model Validation EF Code First allows you to use any validation approach you want when implementing business rules with your model layer.  This enables a great deal of flexibility and power. Starting with this week’s CTP5 release, EF Code First also now includes built-in support for both the DataAnnotation and IValidatorObject validation support built-into .NET 4.  This enables you to easily implement validation rules on your models, and have these rules automatically be enforced by EF Code First whenever you save your model layer.  It provides a very convenient “out of the box” way to enable validation within your applications. Applying DataAnnotations to our Northwind Model The code example below demonstrates how we could add some declarative validation rules to two of the properties of our “Product” model: We are using the [Required] and [Range] attributes above.  These validation attributes live within the System.ComponentModel.DataAnnotations namespace that is built-into .NET 4, and can be used independently of EF.  The error messages specified on them can either be explicitly defined (like above) – or retrieved from resource files (which makes localizing applications easy). Validation Enforcement on SaveChanges() EF Code-First (starting with CTP5) now automatically applies and enforces DataAnnotation rules when a model object is updated or saved.  You do not need to write any code to enforce this – this support is now enabled by default.  This new support means that the below code – which violates our above rules – will automatically throw an exception when we call the “SaveChanges()” method on our Northwind DbContext: The DbEntityValidationException that is raised when the SaveChanges() method is invoked contains a “EntityValidationErrors” property that you can use to retrieve the list of all validation errors that occurred when the model was trying to save.  This enables you to easily guide the user on how to fix them.  Note that EF Code-First will abort the entire transaction of changes if a validation rule is violated – ensuring that our database is always kept in a valid, consistent state. EF Code First’s validation enforcement works both for the built-in .NET DataAnnotation attributes (like Required, Range, RegularExpression, StringLength, etc), as well as for any custom validation rule you create by sub-classing the System.ComponentModel.DataAnnotations.ValidationAttribute base class. UI Validation Support A lot of our UI frameworks in .NET also provide support for DataAnnotation-based validation rules. For example, ASP.NET MVC, ASP.NET Dynamic Data, and Silverlight (via WCF RIA Services) all provide support for displaying client-side validation UI that honor the DataAnnotation rules applied to model objects. The screen-shot below demonstrates how using the default “Add-View” scaffold template within an ASP.NET MVC 3 application will cause appropriate validation error messages to be displayed if appropriate values are not provided: ASP.NET MVC 3 supports both client-side and server-side enforcement of these validation rules.  The error messages displayed are automatically picked up from the declarative validation attributes – eliminating the need for you to write any custom code to display them. Keeping things DRY The “DRY Principle” stands for “Do Not Repeat Yourself”, and is a best practice that recommends that you avoid duplicating logic/configuration/code in multiple places across your application, and instead specify it only once and have it apply everywhere. EF Code First CTP5 now enables you to apply declarative DataAnnotation validations on your model classes (and specify them only once) and then have the validation logic be enforced (and corresponding error messages displayed) across all applications scenarios – including within controllers, views, client-side scripts, and for any custom code that updates and manipulates model classes. This makes it much easier to build good applications with clean code, and to build applications that can rapidly iterate and evolve. Other EF Code First Improvements New to CTP5 EF Code First CTP5 includes a bunch of other improvements as well.  Below are a few short descriptions of some of them: Fluent API Improvements EF Code First allows you to override an “OnModelCreating()” method on the DbContext class to further refine/override the schema mapping rules used to map model classes to underlying database schema.  CTP5 includes some refinements to the ModelBuilder class that is passed to this method which can make defining mapping rules cleaner and more concise.  The ADO.NET Team blogged some samples of how to do this here. Pluggable Conventions Support EF Code First CTP5 provides new support that allows you to override the “default conventions” that EF Code First honors, and optionally replace them with your own set of conventions. New Change Tracking API EF Code First CTP5 exposes a new set of change tracking information that enables you to access Original, Current & Stored values, and State (e.g. Added, Unchanged, Modified, Deleted).  This support is useful in a variety of scenarios. Improved Concurrency Conflict Resolution EF Code First CTP5 provides better exception messages that allow access to the affected object instance and the ability to resolve conflicts using current, original and database values.  Raw SQL Query/Command Support EF Code First CTP5 now allows raw SQL queries and commands (including SPROCs) to be executed via the SqlQuery and SqlCommand methods exposed off of the DbContext.Database property.  The results of these method calls can be materialized into object instances that can be optionally change-tracked by the DbContext.  This is useful for a variety of advanced scenarios. Full Data Annotations Support EF Code First CTP5 now supports all standard DataAnnotations within .NET, and can use them both to perform validation as well as to automatically create the appropriate database schema when EF Code First is used in a database creation scenario.  Summary EF Code First provides an elegant and powerful way to work with data.  I really like it because it is extremely clean and supports best practices, while also enabling solutions to be implemented very, very rapidly.  The code-only approach of the library means that model layers end up being flexible and easy to customize. This week’s CTP5 release further refines EF Code First and helps ensure that it will be really sweet when it ships early next year.  I recommend using NuGet to install and give it a try today.  I think you’ll be pleasantly surprised by how awesome it is. Hope this helps, Scott

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• code metrics for .net code

  - by user20358

  While the code metrics tool gives a pretty good analysis of the code being analyzed, I was wondering if there was any such benchmark on acceptable standards for the following as well: Maximum number of types per assembly Maximum number of such types that can be accessible Maximum number of parameters per method Acceptable RFC count Acceptable Afferent coupling count Acceptable Efferent coupling count Any other metrics to judge the quality of .Net code by? Thanks for your time.

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• What code smell best describes this code?

  - by Paul Stovell

  Suppose you have this code in a class: private DataContext _context; public Customer[] GetCustomers() { GetContext(); return _context.Customers.ToArray(); } public Order[] GetOrders() { GetContext(); return _context.Customers.ToArray(); } // For the sake of this example, a new DataContext is *required* // for every public method call private void GetContext() { if (_context != null) { _context.Dispose(); } _context = new DataContext(); } This code isn't thread-safe - if two calls to GetOrders/GetCustomers are made at the same time from different threads, they may end up using the same context, or the context could be disposed while being used. Even if this bug didn't exist, however, it still "smells" like bad code. A much better design would be for GetContext to always return a new instance of DataContext and to get rid of the private field, and to dispose of the instance when done. Changing from an inappropriate private field to a local variable feels like a better solution. I've looked over the code smell lists and can't find one that describes this. In the past I've thought of it as temporal coupling, but the Wikipedia description suggests that's not the term: Temporal coupling When two actions are bundled together into one module just because they happen to occur at the same time. This page discusses temporal coupling, but the example is the public API of a class, while my question is about the internal design. Does this smell have a name? Or is it simply "buggy code"?

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• Java code critique request [closed]

  - by davidk01

  Can you make sense of the following bit of java code and do you have any suggestions for improving it? Instead of writing four almost identical setOnClickListener method calls I opted to iterate over an array but I'm wondering if this was the best way to do it. Here's the code: /* Set up the radio button click listeners so two categories are not selected at the same time. When one of them is clicked it clears the others. */ final RadioButton[] buttons = {radio_books,radio_games,radio_dvds,radio_electronics}; for (int i = 0; i < 4; i++) { final int k = i; buttons[i].setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { for (int j = 0; j < 4; j++) { if (buttons[j] != buttons[k]) { buttons[j].setChecked(false); } } } }); }

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• Should we enforce code style in our large codebase?

  - by eighttrackmind

  By "code style" I mean 2 things: Style, eg. // bad if(foo){ ... } // good if (foo) { ... } Conventions and idiomaticity, where two ways of writing the same thing are functionally equivalent, but one is more idiomatic. eg. // bad if (fooLib.equals(a, b)) { ... } // good if (a == b) { ... } I think it makes sense to use an auto-formatter to enforce #1 automatically. So my question is specifically about #2. I like to break things down into pros and cons, here's what I've come up with so far: Pros: Used by many large codebases (eg. Google, jQuery) Helps make it a bit easier to work on new areas of the codebase Helps make code more portable (this is not necessarily true) Code style is automatic once you get used to it Makes it easier to fast-decline pull requests Cons: Takes engineers’ and code reviewers’ time away from more important things (like developing features) Code should ideally be rewritten every 2-3 years anyway, so it’s more important to focus on getting the architecture right, and achieving high test coverage Adds strain to code reviews (eg. “don’t do it this way, I like this other way better”) Even if I’ve been using a code style for a while, I still sometime have to pause and think about how to write a line better Having an enforced, uniform code style makes it hard to experiment with potentially better styles Maintaining a style guide takes a lot of incremental effort Engineers rarely read through the style guide. More often, it's cited in code reviews And as a secondary question: we also have many smaller repositories - should the same code style be enforced there?

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• Breadth First Vs Depth First

  - by Ted Smith

  When Traversing a Tree/Graph what is the difference between Breadth First and Depth first? Any coding or pseudocode examples would be great.

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• Is code maintenance typically a special project, or is it considered part of daily work?

  - by blueberryfields

  Earlier, I asked to find out which tools are commonly used to monitor methods and code bases, to find out whether the methods have been getting too long. Most of the responses there suggested that, beyond maintenance on the method currently being edited, programmers don't, in general, keep an eye on the rest of the code base. So I thought I'd ask the question in general: Is code maintenance, in general, considered part of your daily work? Do you find that you're spending at least some of your time cleaning up, refactoring, rewriting code in the code base, to improve it, as part of your other assigned work? Is it expected of you/do you expect it of your teammates? Or is it more common to find that cleanup, refactoring, and general maintenance on the codebase as a whole, occurs in bursts (for example, mostly as part of code reviews, or as part of refactoring/cleaning up projects)?

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• code first CTP5 error message

  - by user482833

  I get the following error message with a new project I have set using code first CTP5. Can't find anything on the web about it. Has anyone encountered this error message? The context cannot be used while the model is being created. This occurs the first time my database context is called (code below): using (StaffData context = new StaffData()) { return context.Employees.Count(e = e.EmployeeReference) == 1; } At this point the database has not been created. I have a database initialiser DropCreateDatabaseIfModelChanges which I set in app_start.

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• breadth first or depth first search

  - by endroix

  I know how this algorithm works, but cant decide when to use which algorithm ? Are there some guidelines, where one better perform than other or any considerations ? Thanks very much.

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• Copyrights concerning code snippets and larger amounts of code

  - by JustcallmeDrago

  I am designing a public code repository. Users will be allowed to post and edit whatever amount of code they want, from code snippets to entire multi-file projects. I have a few major legal concerns about this: Not getting sued/shut down - I feel the site would be a much easier target than tracking down an individual user to sue. I have looked around a bit and see links to legal info in the footer of each page is common. What specific things should I do--and what does does a site such as YouTube (which I see copyrighted material on all the time) do--for protection? Citing sources and editing sourced code - If a user wants to post code that isn't theirs, what concerns/safeguards should I have? Will a link suffice, and what do I need further to allow the code to be edited (to improve it for example)? What can happen if a user posts copyrighted code without citing it? Large chunks of code - What legal differences should I look out for as the amount grows? Not having a mess of licenses for the site - I would like to have a single license (like RosettaCode) that keeps things simple for interaction on the site. I want the code to be postable and editable. I have looked into StackOverflow's CreativeCommons license a little and it says that If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. And on RosettaCode: All software found on Rosetta Code should be considered potentially hazardous. Use at your own risk. Be aware that all code on Rosetta Code is under the GNU Free Documentation License, as are any edits made by contributors. See Rosetta Code:Copyrights for details. What other licenses are like this? Commercializing the site - In what ways can I and can't I make money off of a site that contains code like this? All code will be publicly visible. Initial thoughts are having ads or making money by charging for advanced features.

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• RC of Entity Framework 4.1 (which includes EF Code First)

  - by ScottGu

  Last week the data team shipped the Release Candidate of Entity Framework 4.1.  You can learn more about it and download it here. EF 4.1 includes the new “EF Code First” option that I’ve blogged about several times in the past.  EF Code First provides a really elegant and clean way to work with data, and enables you to do so without requiring a designer or XML mapping file.  Below are links to some tutorials I’ve written in the past about it: Code First Development with Entity Framework 4.x EF Code First: Custom Database Schema Mapping Using EF Code First with an Existing Database The above tutorials were written against the CTP4 release of EF Code First (and so some APIs might be a little different) – but the concepts and scenarios outlined in them are the same as with the RC. Go Live License Last week’s EF 4.1 RC ships with a “go live” license that enables you to use it in production environments.  The final release of EF 4.1 will ship within the next 4 weeks and will be 100% API compatible with the RC release. Improvements with the RC The RC includes several improvements and enhancements.  The EF team has a good blog post summarizing the RC changes.  Scott Hanselman also has a nice video interview with the data team that talks more about the release. One of my favorite improvements introduced with last week’s RC is its support for medium trust security.  This enables you to use EF 4.1 (and code-first) within low-cost ASP.NET shared hosting web environments – without requiring a hoster to install anything to use it. EF 4.1 also now supports validation with not only code-first scenarios, but also model-first and database-first workflows.  Upgrading from previous releases The RC does include a few API tweaks and changes from the prior CTP builds.  Read the release notes that come with the release to get a more detailed listing of the changes. John Papa also has an excellent Upgrading to EF 4.1 RC blog post that describes the steps he took when upgrading a large project he wrote with the previous CTP5 release.  The work to upgrade is pretty straight forward and easy – use his write-up as a guide on how to quickly update projects of your own. NuGet Package Rename One of the changes that the data team made between the CTP5 and RC releases was to rename the NuGet package name from “EFCodeFirst” to “EntityFramework”. They decided to make this change since the EF 4.1 release now includes several additions above and beyond just code first. If you already have installed the “EFCodeFirst” NuGet package, you’ll want to uninstall it and then install the new “EntityFramework” NuGet package.  John Papa’s blog post details the exact steps on how to do this (it only takes ~20 seconds to do this). More EF Tutorials Julie Lerman has created some nice whitepapers and tutorials for MSDN that show using the new EF4 and EF 4.1 feature set. Click here to find links to read and watch them. Summary I’m really excited about the EF 4.1 release that will be shipping next month.  It significantly improves the Entity Framework, and makes it even easier and cleaner to work with data inside of .NET.  You can take advantage of it within all ASP.NET projects (including both Web Forms and MVC), within client projects using Windows Forms and WPF, and within other project types like WCF, Console and Services.  You can use NuGet to easily install it within all of them. Hope this helps, Scott P.S. I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu

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• Design by Contract with Microsoft .Net Code Contract

  - by Fredrik N

  I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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• Generating EF Code First model classes from an existing database

  - by Jon Galloway

  Entity Framework Code First is a lightweight way to "turn on" data access for a simple CLR class. As the name implies, the intended use is that you're writing the code first and thinking about the database later. However, I really like the Entity Framework Code First works, and I want to use it in existing projects and projects with pre-existing databases. For example, MVC Music Store comes with a SQL Express database that's pre-loaded with a catalog of music (including genres, artists, and songs), and while it may eventually make sense to load that seed data from a different source, for the MVC 3 release we wanted to keep using the existing database. While I'm not getting the full benefit of Code First - writing code which drives the database schema - I can still benefit from the simplicity of the lightweight code approach. Scott Guthrie blogged about how to use entity framework with an existing database, looking at how you can override the Entity Framework Code First conventions so that it can work with a database which was created following other conventions. That gives you the information you need to create the model classes manually. However, it turns out that with Entity Framework 4 CTP 5, there's a way to generate the model classes from the database schema. Once the grunt work is done, of course, you can go in and modify the model classes as you'd like, but you can save the time and frustration of figuring out things like mapping SQL database types to .NET types. Note that this template requires Entity Framework 4 CTP 5 or later. You can install EF 4 CTP 5 here. Step One: Generate an EF Model from your existing database The code generation system in Entity Framework works from a model. You can add a model to your existing project and delete it when you're done, but I think it's simpler to just spin up a separate project to generate the model classes. When you're done, you can delete the project without affecting your application, or you may choose to keep it around in case you have other database schema updates which require model changes. I chose to add the Model classes to the Models folder of a new MVC 3 application. Right-click the folder and select "Add / New Item..."   Next, select ADO.NET Entity Data Model from the Data Templates list, and name it whatever you want (the name is unimportant).   Next, select "Generate from database." This is important - it's what kicks off the next few steps, which read your database's schema.   Now it's time to point the Entity Data Model Wizard at your existing database. I'll assume you know how to find your database - if not, I covered that a bit in the MVC Music Store tutorial section on Models and Data. Select your database, uncheck the "Save entity connection settings in Web.config" (since we won't be using them within the application), and click Next.   Now you can select the database objects you'd like modeled. I just selected all tables and clicked Finish.   And there's your model. If you want, you can make additional changes here before going on to generate the code.   Step Two: Add the DbContext Generator Like most code generation systems in Visual Studio lately, Entity Framework uses T4 templates which allow for some control over how the code is generated. K Scott Allen wrote a detailed article on T4 Templates and the Entity Framework on MSDN recently, if you'd like to know more. Fortunately for us, there's already a template that does just what we need without any customization. Right-click a blank space in the Entity Framework model surface and select "Add Code Generation Item..." Select the Code groupt in the Installed Templates section and pick the ADO.NET DbContext Generator. If you don't see this listed, make sure you've got EF 4 CTP 5 installed and that you're looking at the Code templates group. Note that the DbContext Generator template is similar to the EF POCO template which came out last year, but with "fix up" code (unnecessary in EF Code First) removed.   As soon as you do this, you'll two terrifying Security Warnings - unless you click the "Do not show this message again" checkbox the first time. It will also be displayed (twice) every time you rebuild the project, so I checked the box and no immediate harm befell my computer (fingers crossed!).   Here's the payoff: two templates (filenames ending with .tt) have been added to the project, and they've generated the code I needed.   The "MusicStoreEntities.Context.tt" template built a DbContext class which holds the entity collections, and the "MusicStoreEntities.tt" template build a separate class for each table I selected earlier. We'll customize them in the next step. I recommend copying all the generated .cs files into your application at this point, since accidentally rebuilding the generation project will overwrite your changes if you leave them there. Step Three: Modify and use your POCO entity classes Note: I made a bunch of tweaks to my POCO classes after they were generated. You don't have to do any of this, but I think it's important that you can - they're your classes, and EF Code First respects that. Modify them as you need for your application, or don't. The Context class derives from DbContext, which is what turns on the EF Code First features. It holds a DbSet for each entity. Think of DbSet as a simple List, but with Entity Framework features turned on.   //------------------------------------------------------------------------------ // <auto-generated> // This code was generated from a template. // // Changes to this file may cause incorrect behavior and will be lost if // the code is regenerated. // </auto-generated> //------------------------------------------------------------------------------ namespace EF_CodeFirst_From_Existing_Database.Models { using System; using System.Data.Entity; public partial class Entities : DbContext { public Entities() : base("name=Entities") { } public DbSet<Album> Albums { get; set; } public DbSet<Artist> Artists { get; set; } public DbSet<Cart> Carts { get; set; } public DbSet<Genre> Genres { get; set; } public DbSet<OrderDetail> OrderDetails { get; set; } public DbSet<Order> Orders { get; set; } } } It's a pretty lightweight class as generated, so I just took out the comments, set the namespace, removed the constructor, and formatted it a bit. Done. If I wanted, though, I could have added or removed DbSets, overridden conventions, etc. using System.Data.Entity; namespace MvcMusicStore.Models { public class MusicStoreEntities : DbContext { public DbSet Albums { get; set; } public DbSet Genres { get; set; } public DbSet Artists { get; set; } public DbSet Carts { get; set; } public DbSet Orders { get; set; } public DbSet OrderDetails { get; set; } } } Next, it's time to look at the individual classes. Some of mine were pretty simple - for the Cart class, I just need to remove the header and clean up the namespace. //------------------------------------------------------------------------------ // // This code was generated from a template. // // Changes to this file may cause incorrect behavior and will be lost if // the code is regenerated. // //------------------------------------------------------------------------------ namespace EF_CodeFirst_From_Existing_Database.Models { using System; using System.Collections.Generic; public partial class Cart { // Primitive properties public int RecordId { get; set; } public string CartId { get; set; } public int AlbumId { get; set; } public int Count { get; set; } public System.DateTime DateCreated { get; set; } // Navigation properties public virtual Album Album { get; set; } } } I did a bit more customization on the Album class. Here's what was generated: //------------------------------------------------------------------------------ // // This code was generated from a template. // // Changes to this file may cause incorrect behavior and will be lost if // the code is regenerated. // //------------------------------------------------------------------------------ namespace EF_CodeFirst_From_Existing_Database.Models { using System; using System.Collections.Generic; public partial class Album { public Album() { this.Carts = new HashSet(); this.OrderDetails = new HashSet(); } // Primitive properties public int AlbumId { get; set; } public int GenreId { get; set; } public int ArtistId { get; set; } public string Title { get; set; } public decimal Price { get; set; } public string AlbumArtUrl { get; set; } // Navigation properties public virtual Artist Artist { get; set; } public virtual Genre Genre { get; set; } public virtual ICollection Carts { get; set; } public virtual ICollection OrderDetails { get; set; } } } I removed the header, changed the namespace, and removed some of the navigation properties. One nice thing about EF Code First is that you don't have to have a property for each database column or foreign key. In the Music Store sample, for instance, we build the app up using code first and start with just a few columns, adding in fields and navigation properties as the application needs them. EF Code First handles the columsn we've told it about and doesn't complain about the others. Here's the basic class: using System.ComponentModel; using System.ComponentModel.DataAnnotations; using System.Web.Mvc; using System.Collections.Generic; namespace MvcMusicStore.Models { public class Album { public int AlbumId { get; set; } public int GenreId { get; set; } public int ArtistId { get; set; } public string Title { get; set; } public decimal Price { get; set; } public string AlbumArtUrl { get; set; } public virtual Genre Genre { get; set; } public virtual Artist Artist { get; set; } public virtual List OrderDetails { get; set; } } } It's my class, not Entity Framework's, so I'm free to do what I want with it. I added a bunch of MVC 3 annotations for scaffolding and validation support, as shown below: using System.ComponentModel; using System.ComponentModel.DataAnnotations; using System.Web.Mvc; using System.Collections.Generic; namespace MvcMusicStore.Models { [Bind(Exclude = "AlbumId")] public class Album { [ScaffoldColumn(false)] public int AlbumId { get; set; } [DisplayName("Genre")] public int GenreId { get; set; } [DisplayName("Artist")] public int ArtistId { get; set; } [Required(ErrorMessage = "An Album Title is required")] [StringLength(160)] public string Title { get; set; } [Required(ErrorMessage = "Price is required")] [Range(0.01, 100.00, ErrorMessage = "Price must be between 0.01 and 100.00")] public decimal Price { get; set; } [DisplayName("Album Art URL")] [StringLength(1024)] public string AlbumArtUrl { get; set; } public virtual Genre Genre { get; set; } public virtual Artist Artist { get; set; } public virtual List<OrderDetail> OrderDetails { get; set; } } } The end result was that I had working EF Code First model code for the finished application. You can follow along through the tutorial to see how I built up to the finished model classes, starting with simple 2-3 property classes and building up to the full working schema. Thanks to Diego Vega (on the Entity Framework team) for pointing me to the DbContext template.

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• Code First / Database First / Model First : are they just personnal preferences?

  - by Antoine M

  Merely knowing the internal functionality of each approaches, and after reading a lot of posts, I still can't figure out if each one of them is just a matter of personnal preference for the developper or if they deserve different axes of productivity ? Does one of them should be applyed for some specific productivity needs or MS is just beeing kind offering three different flavours ? Should we consider CF as a sort of improvement over DBF or MF and thinking of it as a futur standard on wich spending a peculiar intelectual investment ... ? Is there a link showing a sort of synthetic table with un-passionate pros and cons for each approach, a little bit like for web-forms and MVC. Sorry for those who will find this question redondant. I know it is.

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• Can notes/to-dos in code comments sent to code-reviews result in an effective refactoring process?

  - by dukeofgaming

  I want to start/improve a culture of collective code ownership at my company but at a geographically distributed level... I'd say there is some current collective code-ownership mentality, but only at single geographical sites. This is a follow-up to this question: What is the politically correct way of refactoring other's code? I'm just wondering if submitting *just code comments* for code reviews (we have ReviewBoard, possibly upgrading to Crucible) could actually be an effective mechanism to get the conversation started on improving code, without having others feel territorial about their code. For example, if I add: //ToDo: Refactor this code and that code because of reasons X and Y Then, submit it for code review, and it gets accepted... it could be considered as an agreement (which I think is sometimes harder to get with new code up front). At the same time, the author (and others) might have an easier time digesting and accepting the proposal; rejecting a proposal because it might break things will not longer be a valid reason and therefore the fear of making a change is lost... and at the same time, do not invest 10 hours optimizing something that no one thinks it is worth it and opposes to it just out of fear. This is all conjecture, but I'm feeling something like this (submitting refactoring notes in code comments at the code-review process) would work. Has anyone done something like this in practice?, if so, what have been the results?

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• Inheritance Mapping Strategies with Entity Framework Code First CTP5 Part 1: Table per Hierarchy (TPH)

  - by mortezam

  A simple strategy for mapping classes to database tables might be “one table for every entity persistent class.” This approach sounds simple enough and, indeed, works well until we encounter inheritance. Inheritance is such a visible structural mismatch between the object-oriented and relational worlds because object-oriented systems model both “is a” and “has a” relationships. SQL-based models provide only "has a" relationships between entities; SQL database management systems don’t support type inheritance—and even when it’s available, it’s usually proprietary or incomplete. There are three different approaches to representing an inheritance hierarchy: Table per Hierarchy (TPH): Enable polymorphism by denormalizing the SQL schema, and utilize a type discriminator column that holds type information. Table per Type (TPT): Represent "is a" (inheritance) relationships as "has a" (foreign key) relationships. Table per Concrete class (TPC): Discard polymorphism and inheritance relationships completely from the SQL schema.I will explain each of these strategies in a series of posts and this one is dedicated to TPH. In this series we'll deeply dig into each of these strategies and will learn about "why" to choose them as well as "how" to implement them. Hopefully it will give you a better idea about which strategy to choose in a particular scenario. Inheritance Mapping with Entity Framework Code FirstAll of the inheritance mapping strategies that we discuss in this series will be implemented by EF Code First CTP5. The CTP5 build of the new EF Code First library has been released by ADO.NET team earlier this month. EF Code-First enables a pretty powerful code-centric development workflow for working with data. I’m a big fan of the EF Code First approach, and I’m pretty excited about a lot of productivity and power that it brings. When it comes to inheritance mapping, not only Code First fully supports all the strategies but also gives you ultimate flexibility to work with domain models that involves inheritance. The fluent API for inheritance mapping in CTP5 has been improved a lot and now it's more intuitive and concise in compare to CTP4. A Note For Those Who Follow Other Entity Framework ApproachesIf you are following EF's "Database First" or "Model First" approaches, I still recommend to read this series since although the implementation is Code First specific but the explanations around each of the strategies is perfectly applied to all approaches be it Code First or others. A Note For Those Who are New to Entity Framework and Code-FirstIf you choose to learn EF you've chosen well. If you choose to learn EF with Code First you've done even better. To get started, you can find a great walkthrough by Scott Guthrie here and another one by ADO.NET team here. In this post, I assume you already setup your machine to do Code First development and also that you are familiar with Code First fundamentals and basic concepts. You might also want to check out my other posts on EF Code First like Complex Types and Shared Primary Key Associations. A Top Down Development ScenarioThese posts take a top-down approach; it assumes that you’re starting with a domain model and trying to derive a new SQL schema. Therefore, we start with an existing domain model, implement it in C# and then let Code First create the database schema for us. However, the mapping strategies described are just as relevant if you’re working bottom up, starting with existing database tables. I’ll show some tricks along the way that help you dealing with nonperfect table layouts. Let’s start with the mapping of entity inheritance. -- The Domain ModelIn our domain model, we have a BillingDetail base class which is abstract (note the italic font on the UML class diagram below). We do allow various billing types and represent them as subclasses of BillingDetail class. As for now, we support CreditCard and BankAccount: Implement the Object Model with Code First As always, we start with the POCO classes. Note that in our DbContext, I only define one DbSet for the base class which is BillingDetail. Code First will find the other classes in the hierarchy based on Reachability Convention. public abstract class BillingDetail  {     public int BillingDetailId { get; set; }     public string Owner { get; set; }             public string Number { get; set; } } public class BankAccount : BillingDetail {     public string BankName { get; set; }     public string Swift { get; set; } } public class CreditCard : BillingDetail {     public int CardType { get; set; }                     public string ExpiryMonth { get; set; }     public string ExpiryYear { get; set; } } public class InheritanceMappingContext : DbContext {     public DbSet<BillingDetail> BillingDetails { get; set; } } This object model is all that is needed to enable inheritance with Code First. If you put this in your application you would be able to immediately start working with the database and do CRUD operations. Before going into details about how EF Code First maps this object model to the database, we need to learn about one of the core concepts of inheritance mapping: polymorphic and non-polymorphic queries. Polymorphic Queries LINQ to Entities and EntitySQL, as object-oriented query languages, both support polymorphic queries—that is, queries for instances of a class and all instances of its subclasses, respectively. For example, consider the following query: IQueryable<BillingDetail> linqQuery = from b in context.BillingDetails select b; List<BillingDetail> billingDetails = linqQuery.ToList(); Or the same query in EntitySQL: string eSqlQuery = @"SELECT VAlUE b FROM BillingDetails AS b"; ObjectQuery<BillingDetail> objectQuery = ((IObjectContextAdapter)context).ObjectContext                                                                          .CreateQuery<BillingDetail>(eSqlQuery); List<BillingDetail> billingDetails = objectQuery.ToList(); linqQuery and eSqlQuery are both polymorphic and return a list of objects of the type BillingDetail, which is an abstract class but the actual concrete objects in the list are of the subtypes of BillingDetail: CreditCard and BankAccount. Non-polymorphic QueriesAll LINQ to Entities and EntitySQL queries are polymorphic which return not only instances of the specific entity class to which it refers, but all subclasses of that class as well. On the other hand, Non-polymorphic queries are queries whose polymorphism is restricted and only returns instances of a particular subclass. In LINQ to Entities, this can be specified by using OfType<T>() Method. For example, the following query returns only instances of BankAccount: IQueryable<BankAccount> query = from b in context.BillingDetails.OfType<BankAccount>() select b; EntitySQL has OFTYPE operator that does the same thing: string eSqlQuery = @"SELECT VAlUE b FROM OFTYPE(BillingDetails, Model.BankAccount) AS b"; In fact, the above query with OFTYPE operator is a short form of the following query expression that uses TREAT and IS OF operators: string eSqlQuery = @"SELECT VAlUE TREAT(b as Model.BankAccount)                       FROM BillingDetails AS b                       WHERE b IS OF(Model.BankAccount)"; (Note that in the above query, Model.BankAccount is the fully qualified name for BankAccount class. You need to change "Model" with your own namespace name.) Table per Class Hierarchy (TPH)An entire class hierarchy can be mapped to a single table. This table includes columns for all properties of all classes in the hierarchy. The concrete subclass represented by a particular row is identified by the value of a type discriminator column. You don’t have to do anything special in Code First to enable TPH. It's the default inheritance mapping strategy: This mapping strategy is a winner in terms of both performance and simplicity. It’s the best-performing way to represent polymorphism—both polymorphic and nonpolymorphic queries perform well—and it’s even easy to implement by hand. Ad-hoc reporting is possible without complex joins or unions. Schema evolution is straightforward. Discriminator Column As you can see in the DB schema above, Code First has to add a special column to distinguish between persistent classes: the discriminator. This isn’t a property of the persistent class in our object model; it’s used internally by EF Code First. By default, the column name is "Discriminator", and its type is string. The values defaults to the persistent class names —in this case, “BankAccount” or “CreditCard”. EF Code First automatically sets and retrieves the discriminator values. TPH Requires Properties in SubClasses to be Nullable in the Database TPH has one major problem: Columns for properties declared by subclasses will be nullable in the database. For example, Code First created an (INT, NULL) column to map CardType property in CreditCard class. However, in a typical mapping scenario, Code First always creates an (INT, NOT NULL) column in the database for an int property in persistent class. But in this case, since BankAccount instance won’t have a CardType property, the CardType field must be NULL for that row so Code First creates an (INT, NULL) instead. If your subclasses each define several non-nullable properties, the loss of NOT NULL constraints may be a serious problem from the point of view of data integrity. TPH Violates the Third Normal FormAnother important issue is normalization. We’ve created functional dependencies between nonkey columns, violating the third normal form. Basically, the value of Discriminator column determines the corresponding values of the columns that belong to the subclasses (e.g. BankName) but Discriminator is not part of the primary key for the table. As always, denormalization for performance can be misleading, because it sacrifices long-term stability, maintainability, and the integrity of data for immediate gains that may be also achieved by proper optimization of the SQL execution plans (in other words, ask your DBA). Generated SQL QueryLet's take a look at the SQL statements that EF Code First sends to the database when we write queries in LINQ to Entities or EntitySQL. For example, the polymorphic query for BillingDetails that you saw, generates the following SQL statement: SELECT  [Extent1].[Discriminator] AS [Discriminator],  [Extent1].[BillingDetailId] AS [BillingDetailId],  [Extent1].[Owner] AS [Owner],  [Extent1].[Number] AS [Number],  [Extent1].[BankName] AS [BankName],  [Extent1].[Swift] AS [Swift],  [Extent1].[CardType] AS [CardType],  [Extent1].[ExpiryMonth] AS [ExpiryMonth],  [Extent1].[ExpiryYear] AS [ExpiryYear] FROM [dbo].[BillingDetails] AS [Extent1] WHERE [Extent1].[Discriminator] IN ('BankAccount','CreditCard') Or the non-polymorphic query for the BankAccount subclass generates this SQL statement: SELECT  [Extent1].[BillingDetailId] AS [BillingDetailId],  [Extent1].[Owner] AS [Owner],  [Extent1].[Number] AS [Number],  [Extent1].[BankName] AS [BankName],  [Extent1].[Swift] AS [Swift] FROM [dbo].[BillingDetails] AS [Extent1] WHERE [Extent1].[Discriminator] = 'BankAccount' Note how Code First adds a restriction on the discriminator column and also how it only selects those columns that belong to BankAccount entity. Change Discriminator Column Data Type and Values With Fluent API Sometimes, especially in legacy schemas, you need to override the conventions for the discriminator column so that Code First can work with the schema. The following fluent API code will change the discriminator column name to "BillingDetailType" and the values to "BA" and "CC" for BankAccount and CreditCard respectively: protected override void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder) {     modelBuilder.Entity<BillingDetail>()                 .Map<BankAccount>(m => m.Requires("BillingDetailType").HasValue("BA"))                 .Map<CreditCard>(m => m.Requires("BillingDetailType").HasValue("CC")); } Also, changing the data type of discriminator column is interesting. In the above code, we passed strings to HasValue method but this method has been defined to accepts a type of object: public void HasValue(object value); Therefore, if for example we pass a value of type int to it then Code First not only use our desired values (i.e. 1 & 2) in the discriminator column but also changes the column type to be (INT, NOT NULL): modelBuilder.Entity<BillingDetail>()             .Map<BankAccount>(m => m.Requires("BillingDetailType").HasValue(1))             .Map<CreditCard>(m => m.Requires("BillingDetailType").HasValue(2)); SummaryIn this post we learned about Table per Hierarchy as the default mapping strategy in Code First. The disadvantages of the TPH strategy may be too serious for your design—after all, denormalized schemas can become a major burden in the long run. Your DBA may not like it at all. In the next post, we will learn about Table per Type (TPT) strategy that doesn’t expose you to this problem. References ADO.NET team blog Java Persistence with Hibernate book a { text-decoration: none; } a:visited { color: Blue; } .title { padding-bottom: 5px; font-family: Segoe UI; font-size: 11pt; font-weight: bold; padding-top: 15px; } .code, .typeName { font-family: consolas; } .typeName { color: #2b91af; } .padTop5 { padding-top: 5px; } .padTop10 { padding-top: 10px; } p.MsoNormal { margin-top: 0in; margin-right: 0in; margin-bottom: 10.0pt; margin-left: 0in; line-height: 115%; font-size: 11.0pt; font-family: "Calibri" , "sans-serif"; }

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• EF 6 Code First Many to many With Payload and self referencing many to many

  - by lesley86

  I Have the problem where i have a many to many relationship and on one of the tables there will be a self referencing many to many. So basically a school have zero or many groups and many groups can have 0 or many schools. The groups table will contain a parent child many to many with itself because a group can be a child of another group or it can have no children and that child can have a child, one child can also have many parents or a entity can have no parents. I created a mapping table with Payload to solvethe first many to many problem. code snippet public class School { public virtual ICollection<SchoolGroupMap> SchoolGroupMaps } public class SchoolGroup { public virtual ICollection<SchoolGroupMap> SchoolGroupMaps } public class SchoolGroupMap { public virtual School School public virtual SchoolGroup SchoolGroup } i Then tried modifying the code the following way for the the self referencing many to many public class SchoolGroup { public virtual ICollection<SchoolGroupMap> SchoolGroupMaps public virtual ICollection<SchoolGroup> Parents public virtual ICollection<SchoolGroup> Children } I changed the context with has many and an auto mapping table (forgive me i have been trying so many things today i do not have the exact code). I received an error the properties on the classes must match. Can anyone help please. I want to do create navigation properties on the self referencing many to many. Also a seed example would be appreciated regards

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• Writing/discussions about the aesthetics of code?

  - by dilettante.coder

  I'm looking for considerations of the questions "Can code be beautiful?" and "What makes code beautiful?" Examples would include: This academic paper: Obfuscation, Weird Languages, and Code Aesthetics This blog post: Hamon or the Skin Deep Beauty of Code Please note that I'm not trying to start a discussion here, or asking for opinions about what makes code beautiful, or for code you think is beautiful; I'm trying to find stuff that has already been published. Thanks for your help.

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• Do abstractions have to reduce code readability?

  - by Martin Blore

  A good developer I work with told me recently about some difficulty he had in implementing a feature in some code we had inherited; he said the problem was that the code was difficult to follow. From that, I looked deeper into the product and realised how difficult it was to see the code path. It used so many interfaces and abstract layers, that trying to understand where things began and ended was quite difficult. It got me thinking about the times I had looked at past projects (before I was so aware of clean code principles) and found it extremely difficult to get around in the project, mainly because my code navigation tools would always land me at an interface. It would take a lot of extra effort to find the concrete implementation or where something was wired up in some plugin type architecture. I know some developers strictly turn down dependency injection containers for this very reason. It confuses the path of the software so much that the difficulty of code navigation is exponentially increased. My question is: when a framework or pattern introduces so much overhead like this, is it worth it? Is it a symptom of a poorly implemented pattern? I guess a developer should look to the bigger picture of what that abstractions brings to the project to help them get through the frustration. Usually though, it's difficult to make them see that big picture. I know I've failed to sell the needs of IOC and DI with TDD. For those developers, use of those tools just cramps code readability far too much.

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• Please recommend citations for source code documentation standards

  - by Aerik

  I'm trying to convince another group in my company that they need to provide more documentation in their source code (they want to hand off the code to my group) but they're treating it as a "nice to have". In my view, it's a necessity. I've run a source code analysis tool and it's showing about 10% comment lines - but looking at the source code, most of that is coming from entire functions that the author has commented out. Can anyone provide some authoritative citations / references for documentation / comment standards for source code? (In case it matters, we're a C# house, with a little Matlab thrown in).

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• Does code-generation increase the code quality?

  - by platzhirsch

  Arguing for code-generation I am looking for some reasons, if howsoever, code generation increases the code quality, respectively is in favor for quality insurance. To clarify what I mean with code-generation I can talk only about a project of mine: We use XML files to describe different relationships, in fact our database schema. These XML files are used to generate our ORM framework and HTML forms which can be used to add, delete and modify entities. To my mind, it increases the quality, as the human error is reduced. If someone was implemented wrong, it is broken in the model. This is good, because the error might appear a lot faster, as more generated code is broken, too.

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• How to measure code quality? [closed]

  - by Lo Wai Lun

  Is there a methodology or any objective standard to determine whether the code of the project is well-written? How to measure in a structural and scientific manner to access the quality of the code? Many people say code review is important and always do encapsulation and data abstraction to ensure the quality. How can we determine the quality? Can a structural, organised software design diagrams drawn implies good quality of code ? If we type the code with good cautions of encapsulation and data abstraction, why review anyway?

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