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  • Flex Nested Drag And Drop

    - by Soumitra
    i have a canvas where i can add layout say another canvas.So both the canvas have drag enter and drag drop event . I want to toggle this events .. i.e when outer canvas will accept drag inner will not accept and when inner will accept drag outer will not.I am facing a problem in nested drop events..Inner drop event is not working..Please help me out..Waiting for your help

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  • How to cancel a deeply nested process

    - by Mystere Man
    I have a class that is a "manager" sort of class. One of it's functions is to signal that the long running process of the class should shut down. It does this by setting a boolean called "IsStopping" in class. public class Foo { bool isStoping void DoWork() { while (!isStopping) { // do work... } } } Now, DoWork() was a gigantic function, and I decided to refactor it out and as part of the process broke some of it into other classes. The problem is, Some of these classes also have long running functions that need to check if isStopping is true. public class Foo { bool isStoping void DoWork() { while (!isStopping) { MoreWork mw = new MoreWork() mw.DoMoreWork() // possibly long running // do work... } } } What are my options here? I have considered passing isStopping by reference, which I don't really like because it requires there to be an outside object. I would prefer to make the additional classes as stand alone and dependancy free as possible. I have also considered making isStopping a property, and then then having it call an event that the inner classes could be subscribed to, but this seems overly complex. Another option was to create a "Process Cancelation Token" class, similar to what .net 4 Tasks use, then that token be passed to those classes. How have you handled this situation? EDIT: Also consider that MoreWork might have a EvenMoreWork object that it instantiates and calls a potentially long running method on... and so on. I guess what i'm looking for is a way to be able to signal an arbitrary number of objects down a call tree to tell them to stop what they're doing and clean up and return.

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  • C++ creating generic template function specialisations

    - by Fire Lancer
    I know how to specialise a template function, however what I want to do here is specialise a function for all types which have a given method, eg: template<typename T> void foo(){...} template<typename T, if_exists(T::bar)>void foo(){...}//always use this one if the method T::bar exists T::bar in my classes is static and has different return types. I tried doing this by having an empty base class ("class HasBar{};") for my classes to derive from and using boost::enable_if with boost::is_base_of on my "specialised" version. However the problem then is that for classes that do have bar, the compiler cant resolve which one to use :(. template<typename T> typename boost::enable_if<boost::is_base_of(HasBar, T>, void>::type f() {...} I know that I could use boost::disable_if on the "normal" version, however I do not control the normal version (its provided by a third party library and its expected for specialisations to be made, I just don't really want to make explicit specialisations for my 20 or so classes), nor do I have that much control over the code using these functions, just the classes implementing T::bar and the function that uses it. Is there some way to tell the compiler to "always use this version if possible no matter what" without altering the other versions?

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  • Documentation tool for .net applications

    - by jovialwhispers
    I have an ASP.NET 2.0 application, developed in the early days of 2.0. There are almost no comment tags in the application. Is there any tool which can grab all the classes from that application generate a report [in chm or html or pdf] with all the classes and belonging methods, hierarchy of the classes and any kind of visual presentation of the over all flow/relationship/architecture? Thanks

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  • JUnit : Is there a way to skip a test belonging to a Test class's parent?

    - by Jon
    I have two classes: public abstract class AbstractFoobar { ... } and public class ConcreteFoobar extends AbstractFoobar { ... } I have corresponding test classes for these two classes: public class AbstractFoobarTest { ... } and public class ConcreteFoobarTest extends AbstractFoobarTest { ... } When I run ConcreteFoobarTest (in JUnit), the annotated @Test methods in AbstractFoobarTest get run along with those declared directly on ConcreteFoobarTest because they are inherited. Is there anyway to skip them?

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  • Reloading Rails Directories on Change for Development, Not in Lib

    - by yar
    I have checked out several questions on this, including all of those you see next to the question. Unfortunately, I'm not working with a plugin, and I don't want to work in lib. I have a directory called File.join(Rails.root, 'classes') and I'd like the classes in this directory to reload automatically in dev. In my environment.rb I have this line config.load_paths << File.join(Rails.root, 'classes') which works fine and blows up if the path isn't there. The reloading line in my development.rb also works fine require_dependency File.join(Rails.root, 'classes', 'blah.rb') which blows up if the file is not there (a good sign). However, the file doesn't reload. This all works if the file is in the root of lib and I use the require_dependency line, but my whole point is to get stuff out of lib as suggested here.

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  • Java how does Key Event Handling Mechanism(KeyListeners notified) work ?

    - by Carbonizer
    How does application/JVM know which classes if implemented key handling interfaces ? Does it use java Reflections or does it check all the classes for methods ? How can a application or executing JVM understanding to deliver the user event or call the specific methods on a class that implemented the keylistener interface. Does it look at all the classes if those methods are implemented or how does it know which classes implmented keylistener interface ? If you dont implement the keylistener Interface for a class but still implmentation all its methods. Do the class still process the user event occurred ?

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  • iOS TableView crash don't know how. Here is the app

    - by jollyr0ger
    Hi! In my app that you can download here: http://ge.tt/2DDqfJa I've started a discussion but is died here iOS TableView crash loading different data The problem is when I back from viewing the YouTube video to the recipes list, the app crash... And when i select a category for the second time, where have to load a tableview with different data source, it crash. This is the crash log Program received signal: “EXC_BAD_ACCESS”. (gdb) bt #0 0x00f0da63 in objc_msgSend () #1 0x04b27ca0 in ?? () #2 0x00002665 in -[RecipesListController viewWillAppear:] (self=0x4b38a00, _cmd=0x6d81a2, animated=1 '\001') at /Users/claudiocanino/Documents/iOS/CottoMangiato/Classes/RecipesListController.m:67 #3 0x00370c9a in -[UINavigationController _startTransition:fromViewController:toViewController:] () #4 0x0036b606 in -[UINavigationController _startDeferredTransitionIfNeeded] () #5 0x0037283e in -[UINavigationController pushViewController:transition:forceImmediate:] () #6 0x04f49549 in -[UINavigationControllerAccessibility(SafeCategory) pushViewController:transition:forceImmediate:] () #7 0x0036b4a0 in -[UINavigationController pushViewController:animated:] () #8 0x00003919 in -[CategoryViewController tableView:didSelectRowAtIndexPath:] (self=0x4b27ca0, _cmd=0x6d19e3, tableView=0x500c200, indexPath=0x4b2d650) at /Users/claudiocanino/Documents/iOS/CottoMangiato/Classes/CategoryViewCotroller.m:104 #9 0x0032a794 in -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] () #10 0x00320d50 in -[UITableView _userSelectRowAtPendingSelectionIndexPath:] () #11 0x000337f6 in __NSFireDelayedPerform () #12 0x00d8cfe3 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ () #13 0x00d8e594 in __CFRunLoopDoTimer () #14 0x00ceacc9 in __CFRunLoopRun () #15 0x00cea240 in CFRunLoopRunSpecific () #16 0x00cea161 in CFRunLoopRunInMode () #17 0x016e0268 in GSEventRunModal () #18 0x016e032d in GSEventRun () #19 0x002c342e in UIApplicationMain () #20 0x00001c08 in main (argc=1, argv=0xbfffef58) at /Users/claudiocanino/Documents/iOS/CottoMangiato/main.m:15 Another bt log: (gdb) bt #0 0x00cd76a1 in __CFBasicHashDeallocate () #1 0x00cc2bcb in _CFRelease () #2 0x00002dd6 in -[RecipesListController setRecipesArray:] (self=0x6834d50, _cmd=0x4293, _value=0x4e3bc70) at /Users/claudiocanino/Documents/iOS/CottoMangiato/Classes/RecipesListController.m:16 #3 0x00002665 in -[RecipesListController viewWillAppear:] (self=0x6834d50, _cmd=0x6d81a2, animated=1 '\001') at /Users/claudiocanino/Documents/iOS/CottoMangiato/Classes/RecipesListController.m:67 #4 0x00370c9a in -[UINavigationController _startTransition:fromViewController:toViewController:] () #5 0x0036b606 in -[UINavigationController _startDeferredTransitionIfNeeded] () #6 0x0037283e in -[UINavigationController pushViewController:transition:forceImmediate:] () #7 0x091ac549 in -[UINavigationControllerAccessibility(SafeCategory) pushViewController:transition:forceImmediate:] () #8 0x0036b4a0 in -[UINavigationController pushViewController:animated:] () #9 0x00003919 in -[CategoryViewController tableView:didSelectRowAtIndexPath:] (self=0x4b12970, _cmd=0x6d19e3, tableView=0x5014400, indexPath=0x4b2bd00) at /Users/claudiocanino/Documents/iOS/CottoMangiato/Classes/CategoryViewCotroller.m:104 #10 0x0032a794 in -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] () #11 0x00320d50 in -[UITableView _userSelectRowAtPendingSelectionIndexPath:] () #12 0x000337f6 in __NSFireDelayedPerform () #13 0x00d8cfe3 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ () #14 0x00d8e594 in __CFRunLoopDoTimer () #15 0x00ceacc9 in __CFRunLoopRun () #16 0x00cea240 in CFRunLoopRunSpecific () #17 0x00cea161 in CFRunLoopRunInMode () #18 0x016e0268 in GSEventRunModal () #19 0x016e032d in GSEventRun () #20 0x002c342e in UIApplicationMain () #21 0x00001c08 in main (argc=1, argv=0xbfffef58) at /Users/claudiocanino/Documents/iOS/CottoMangiato/main.m:15 Thanks

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  • Call c++ function pointer from c#

    - by Sam
    Is it possible to call a c(++) static function pointer like this typedef int (*MyCppFunc)(void* SomeObject); from c#? void CallFromCSharp(MyCppFunc funcptr, IntPtr param) { funcptr(param); } I need to be able to callback from c# into some old c++ classes. C++ is managed, but the classes are not ref classes (yet). So far I got no idea how to call a c++ function pointer from c#, is it possible?

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  • combining results of two select statements

    - by ErnieStings
    I'm using T-SQL with ASP.NET, and c# and i'm pretty new to SQL. I was wondering how i could combine the results of two queries Query1: SELECT tableA.Id, tableA.Name, [tableB].Username AS Owner, [tableB].ImageUrl, [tableB].CompanyImageUrl, COUNT(tableD.UserId) AS NumberOfUsers FROM tableD RIGHT OUTER JOIN [tableB] INNER JOIN tableA ON [tableB].Id = tableA.Owner ON tableD.tableAId = tableA.Id GROUP BY tableA.Name, [tableB].Username, [tableB].ImageUrl, [tableB].CompanyImageUrl Query2: SELECT tableA.Id, tableA.Name, COUNT([tableC].Id) AS NumberOfPlans FROM [tableC] RIGHT OUTER JOIN tableA ON [tableC].tableAId = tableA.Id GROUP BY tableA.Id, tableA.Name Any help would be much appreciated. Thanks in advance

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  • Mysql filling in missing dates

    - by bsandrabr
    I have the following query SELECT * FROM attend RIGHT OUTER JOIN noattend ON attend.date = noattend.date2 WHERE attend.date BETWEEN '2010-02-01' AND '2010-04-01' AND attend.customerid =1 ORDER BY date DESC LIMIT 0 , 30 Attend is the table with customerid noattend is the table with a row for each date (date2) I followed the advice in other questions to right outer join it to create values where there is no record in attend but it still isn't filling in the empties any help much appreciated

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  • C++ dynamic type construction and detection

    - by KneLL
    There was an interesting problem in C++, but it concerns more likely architecture. There are many (10, 20, 40, etc) classes that describe some characteristics (mix-in classes), for exmaple: struct Base { virtual ~Base() {} }; struct A : virtual public Base { int size; }; struct B : virtual public Base { float x, y; }; struct C : virtual public Base { bool some_bool_state; }; struct D : virtual public Base { string str; } // .... Primary module declares and exports a function (for simplicity just function declarations without classes): // .h file void operate(Base *pBase); // .cpp file void operate(Base *pBase) { // .... } Any other module can has a code like this: #include "mixins.h" #include "primary.h" class obj1_t : public A, public C, public D {}; class obj2_t : public B, public D {}; // ... void Pass() { obj1_t obj1; obj2_t obj2; operate(&obj1); operate(&obj2); } The question is how to know what the real type of given object in operate() without dynamic_cast and any type information in classes (constants, etc)? Function operate() is used with big array of objects in small time periods and dynamic_cast is too slow for it. And I don't want to include constants (enum obj_type { ... }) because this is not OOP-way. // module operate.cpp void some_operate(Base *pBase) { processA(pBase); processB(pBase); } void processA(A *pA) { } void processB(B *pB) { } I cannot directly pass a pBase to these functions. And it's impossible to have all possible combinations of classes, because I can add new classes just by including new .h files. As one of solutions that comed to mind, in editor application I can use a composite container: struct CompositeObject { vector<Base *pBase> parts; }; But editor does not need a time optimization and can use dynamic_cast for parts to determine the exact type. In operate() I cannot use this solution. So, is it possible to not use a dynamic_cast and type information to solve this problem? Or maybe I should use another architecture?

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  • C# InternalsVisibleTo() attribute for VBNET 2.0 while testing?

    - by Will Marcouiller
    I'm building an Active Directory wrapper in VBNET 2.0 (can't use later .NET) in which I have the following: IUtilisateur IGroupe IUniteOrganisation These interfaces are implemented in internal classes (Friend in VBNET), so that I want to implement a façade in order to instiate each of the interfaces with their internal classes. This will allow the architecture a better flexibility, etc. Now, I want to test these classes (Utilisateur, Groupe, UniteOrganisation) in a different project within the same solution. However, these classes are internal. I would like to be able to instantiate them without going through my façade, but only for these tests, nothing more. Here's a piece of code to illustrate it: public static class DirectoryFacade { public static IGroupe CreerGroupe() { return new Groupe(); } } // Then in code, I would write something alike: public partial class MainForm : Form { public MainForm() { IGroupe g = DirectoryFacade.CreerGroupe(); // Doing stuff with instance here... } } // My sample interface: public interface IGroupe { string Domaine { get; set; } IList<IUtilisateur> Membres { get; } } internal class Groupe : IGroupe { private IList<IUtilisateur> _membres; internal Groupe() { _membres = new List<IUtilisateur>(); } public string Domaine { get; set; } public IList<IUtilisateur> Membres { get { return _membres; } } } I heard of InternalsVisibleTo() attribute, recently. I was wondering whether it is available in VBNET 2.0/VS2005 so that I could access the assmebly's internal classes for my tests? Otherwise, how could I achieve this?

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  • CSS - How can I center a div within a div?

    - by Spines
    I have an outer div that is 800px wide. I have an inner div that could be anywhere from 200 to 600px wide. I know how to center the inner div within the outer one if I set the inner one to have a specific width, but how do I center it since its a variable width? Is there a way to set the div to only be the width of the elements inside of it, rather than having it expand to fill its containing div?

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  • Silently binding a variable instance to a class in C++?

    - by gct
    So I've got a plugin-based system I'm writing. Users can create a child class of a Plugin class and then it will be loaded at runtime and integrated with the rest of the system. When a Plugin is run from the system, it's run in the context of a group of plugins, which I call a Session. My problem is that inside the user plugins, two streaming classes called pf_ostream and pf_istream can be used to read/write data to the system. I'd like to bind the plugin instance's session variable to pf_ostream and pf_istream somehow so that when the user instantiates those classes, it's already bound to the session for them (basically I don't want them to see the session internals) I could just do this with a macro, wrapping a call to the constructor like: #define MAKE_OSTREAM = pf_ostream_int(this->session) But I thought there might be a better way. I looked at using a nested class inside Plugin wrapping pf_ostream but it appears nested classes don't get access to the enclosing classes variables in a closure sort of way. Does anyone know of a neat way to do this?

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  • multiple join query in entity framework

    - by gvLearner
    I have following tables tasks id | name | proj_id 1 | task1 | 1 2 | task2 | 1 3 | task3 | 1 projects id | name 1 | sample proj1 2 | demo project budget_versions id | version_name| proj_id 1 | 50 | 1 budgets id | cost | budget_version_id | task_id 1 | 3000 | 1 | 2 2 | 5000 | 1 | 1 I need to join these tables to get a result as below task_id | task_name | project_id | budget_version | budget_id | cost 1 | task1 | 1 | 1 | 2 |5000 2 | task2 | 1 | 1 | 1 |3000 3 | task3 | 1 | NULL | NULL |NULL select tsk.id,tsk.name, tsk.project_id, bgtver.id, bgt.id, bgt.cost from TASK tsk left outer join BUDGET_VERSIONS bgtver on tsk.project_id= bgtver.project_id left outer join BUDGETS bgt on bgtver.id = bgt.budget_version_id and tsk.id = bgt.task_id where bgtver.id = 1

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  • Does Java not support multiple inheritance?

    - by user1720616
    Lets us take instances of two classes public abstract class Shapes { public abstract void draw(Graphics g); } public class Rectangle extends Shapes { public void draw(Graphics g) { //implementation of the method } } here the class Rectangle has extended class Shapes and implicitly it extends class Object.I know no other extension is possible but cant we call inheriting classes Shapes and Object multiple inheritance?(Since inheriting two classes is multiple inheritance from one perspective)

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  • Qt Should I derive from QDataStream?

    - by ShaChris23
    I'm currently using QDataStream to serialize my classes. I have quite a few number of my own classes that I serialize often. Should I derive QDataStream to create my own DataStream class? Or is there a better pattern than this? Note that these custom classes are used by many of our projects, so maybe doing so will make coding easier. Another way to phrase this question is: when a framework provides you with a serialization class, how do you handle serializing your own custom-type classes such that you don't have to remember how to serialize them everytime.

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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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  • Code Reuse is (Damn) Hard

    - by James Michael Hare
    Being a development team lead, the task of interviewing new candidates was part of my job.  Like any typical interview, we started with some easy questions to get them warmed up and help calm their nerves before hitting the hard stuff. One of those easier questions was almost always: “Name some benefits of object-oriented development.”  Nearly every time, the candidate would chime in with a plethora of canned answers which typically included: “it helps ease code reuse.”  Of course, this is a gross oversimplification.  Tools only ease reuse, its developers that ultimately can cause code to be reusable or not, regardless of the language or methodology. But it did get me thinking…  we always used to say that as part of our mantra as to why Object-Oriented Programming was so great.  With polymorphism, inheritance, encapsulation, etc. we in essence set up the concepts to help facilitate reuse as much as possible.  And yes, as a developer now of many years, I unquestionably held that belief for ages before it really struck me how my views on reuse have jaded over the years.  In fact, in many ways Agile rightly eschews reuse as taking a backseat to developing what's needed for the here and now.  It used to be I was in complete opposition to that view, but more and more I've come to see the logic in it.  Too many times I've seen developers (myself included) get lost in design paralysis trying to come up with the perfect abstraction that would stand all time.  Nearly without fail, all of these pieces of code become obsolete in a matter of months or years. It’s not that I don’t like reuse – it’s just that reuse is hard.  In fact, reuse is DAMN hard.  Many times it is just a distraction that eats up architect and developer time, and worse yet can be counter-productive and force wrong decisions.  Now don’t get me wrong, I love the idea of reusable code when it makes sense.  These are in the few cases where you are designing something that is inherently reusable.  The problem is, most business-class code is inherently unfit for reuse! Furthermore, the code that is reusable will often fail to be reused if you don’t have the proper framework in place for effective reuse that includes standardized versioning, building, releasing, and documenting the components.  That should always be standard across the board when promoting reusable code.  All of this is hard, and it should only be done when you have code that is truly reusable or you will be exerting a large amount of development effort for very little bang for your buck. But my goal here is not to get into how to reuse (that is a topic unto itself) but what should be reused.  First, let’s look at an extension method.  There’s many times where I want to kick off a thread to handle a task, then when I want to reign that thread in of course I want to do a Join on it.  But what if I only want to wait a limited amount of time and then Abort?  Well, I could of course write that logic out by hand each time, but it seemed like a great extension method: 1: public static class ThreadExtensions 2: { 3: public static bool JoinOrAbort(this Thread thread, TimeSpan timeToWait) 4: { 5: bool isJoined = false; 6:  7: if (thread != null) 8: { 9: isJoined = thread.Join(timeToWait); 10:  11: if (!isJoined) 12: { 13: thread.Abort(); 14: } 15: } 16: return isJoined; 17: } 18: } 19:  When I look at this code, I can immediately see things that jump out at me as reasons why this code is very reusable.  Some of them are standard OO principles, and some are kind-of home grown litmus tests: Single Responsibility Principle (SRP) – The only reason this extension method need change is if the Thread class itself changes (one responsibility). Stable Dependencies Principle (SDP) – This method only depends on classes that are more stable than it is (System.Threading.Thread), and in itself is very stable, hence other classes may safely depend on it. It is also not dependent on any business domain, and thus isn't subject to changes as the business itself changes. Open-Closed Principle (OCP) – This class is inherently closed to change. Small and Stable Problem Domain – This method only cares about System.Threading.Thread. All-or-None Usage – A user of a reusable class should want the functionality of that class, not parts of that functionality.  That’s not to say they most use every method, but they shouldn’t be using a method just to get half of its result. Cost of Reuse vs. Cost to Recreate – since this class is highly stable and minimally complex, we can offer it up for reuse very cheaply by promoting it as “ready-to-go” and already unit tested (important!) and available through a standard release cycle (very important!). Okay, all seems good there, now lets look at an entity and DAO.  I don’t know about you all, but there have been times I’ve been in organizations that get the grand idea that all DAOs and entities should be standardized and shared.  While this may work for small or static organizations, it’s near ludicrous for anything large or volatile. 1: namespace Shared.Entities 2: { 3: public class Account 4: { 5: public int Id { get; set; } 6:  7: public string Name { get; set; } 8:  9: public Address HomeAddress { get; set; } 10:  11: public int Age { get; set;} 12:  13: public DateTime LastUsed { get; set; } 14:  15: // etc, etc, etc... 16: } 17: } 18:  19: ... 20:  21: namespace Shared.DataAccess 22: { 23: public class AccountDao 24: { 25: public Account FindAccount(int id) 26: { 27: // dao logic to query and return account 28: } 29:  30: ... 31:  32: } 33: } Now to be fair, I’m not saying there doesn’t exist an organization where some entites may be extremely static and unchanging.  But at best such entities and DAOs will be problematic cases of reuse.  Let’s examine those same tests: Single Responsibility Principle (SRP) – The reasons to change for these classes will be strongly dependent on what the definition of the account is which can change over time and may have multiple influences depending on the number of systems an account can cover. Stable Dependencies Principle (SDP) – This method depends on the data model beneath itself which also is largely dependent on the business definition of an account which can be very inherently unstable. Open-Closed Principle (OCP) – This class is not really closed for modification.  Every time the account definition may change, you’d need to modify this class. Small and Stable Problem Domain – The definition of an account is inherently unstable and in fact may be very large.  What if you are designing a system that aggregates account information from several sources? All-or-None Usage – What if your view of the account encompasses data from 3 different sources but you only care about one of those sources or one piece of data?  Should you have to take the hit of looking up all the other data?  On the other hand, should you have ten different methods returning portions of data in chunks people tend to ask for?  Neither is really a great solution. Cost of Reuse vs. Cost to Recreate – DAOs are really trivial to rewrite, and unless your definition of an account is EXTREMELY stable, the cost to promote, support, and release a reusable account entity and DAO are usually far higher than the cost to recreate as needed. It’s no accident that my case for reuse was a utility class and my case for non-reuse was an entity/DAO.  In general, the smaller and more stable an abstraction is, the higher its level of reuse.  When I became the lead of the Shared Components Committee at my workplace, one of the original goals we looked at satisfying was to find (or create), version, release, and promote a shared library of common utility classes, frameworks, and data access objects.  Now, of course, many of you will point to nHibernate and Entity for the latter, but we were looking at larger, macro collections of data that span multiple data sources of varying types (databases, web services, etc). As we got deeper and deeper in the details of how to manage and release these items, it quickly became apparent that while the case for reuse was typically a slam dunk for utilities and frameworks, the data access objects just didn’t “smell” right.  We ended up having session after session of design meetings to try and find the right way to share these data access components. When someone asked me why it was taking so long to iron out the shared entities, my response was quite simple, “Reuse is hard...”  And that’s when I realized, that while reuse is an awesome goal and we should strive to make code maintainable, often times you end up creating far more work for yourself than necessary by trying to force code to be reusable that inherently isn’t. Think about classes the times you’ve worked in a company where in the design session people fight over the best way to implement a class to make it maximally reusable, extensible, and any other buzzwordable.  Then think about how quickly that design became obsolete.  Many times I set out to do a project and think, “yes, this is the best design, I can extend it easily!” only to find out the business requirements change COMPLETELY in such a way that the design is rendered invalid.  Code, in general, tends to rust and age over time.  As such, writing reusable code can often be difficult and many times ends up being a futile exercise and worse yet, sometimes makes the code harder to maintain because it obfuscates the design in the name of extensibility or reusability. So what do I think are reusable components? Generic Utility classes – these tend to be small classes that assist in a task and have no business context whatsoever. Implementation Abstraction Frameworks – home-grown frameworks that try to isolate changes to third party products you may be depending on (like writing a messaging abstraction layer for publishing/subscribing that is independent of whether you use JMS, MSMQ, etc). Simplification and Uniformity Frameworks – To some extent this is similar to an abstraction framework, but there may be one chosen provider but a development shop mandate to perform certain complex items in a certain way.  Or, perhaps to simplify and dumb-down a complex task for the average developer (such as implementing a particular development-shop’s method of encryption). And what are less reusable? Application and Business Layers – tend to fluctuate a lot as requirements change and new features are added, so tend to be an unstable dependency.  May be reused across applications but also very volatile. Entities and Data Access Layers – these tend to be tuned to the scope of the application, so reusing them can be hard unless the abstract is very stable. So what’s the big lesson?  Reuse is hard.  In fact it’s damn hard.  And much of the time I’m not convinced we should focus too hard on it. If you’re designing a utility or framework, then by all means design it for reuse.  But you most also really set down a good versioning, release, and documentation process to maximize your chances.  For anything else, design it to be maintainable and extendable, but don’t waste the effort on reusability for something that most likely will be obsolete in a year or two anyway.

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  • When is a SQL function not a function?

    - by Rob Farley
    Should SQL Server even have functions? (Oh yeah – this is a T-SQL Tuesday post, hosted this month by Brad Schulz) Functions serve an important part of programming, in almost any language. A function is a piece of code that is designed to return something, as opposed to a piece of code which isn’t designed to return anything (which is known as a procedure). SQL Server is no different. You can call stored procedures, even from within other stored procedures, and you can call functions and use these in other queries. Stored procedures might query something, and therefore ‘return data’, but a function in SQL is considered to have the type of the thing returned, and can be used accordingly in queries. Consider the internal GETDATE() function. SELECT GETDATE(), SomeDatetimeColumn FROM dbo.SomeTable; There’s no logical difference between the field that is being returned by the function and the field that’s being returned by the table column. Both are the datetime field – if you didn’t have inside knowledge, you wouldn’t necessarily be able to tell which was which. And so as developers, we find ourselves wanting to create functions that return all kinds of things – functions which look up values based on codes, functions which do string manipulation, and so on. But it’s rubbish. Ok, it’s not all rubbish, but it mostly is. And this isn’t even considering the SARGability impact. It’s far more significant than that. (When I say the SARGability aspect, I mean “because you’re unlikely to have an index on the result of some function that’s applied to a column, so try to invert the function and query the column in an unchanged manner”) I’m going to consider the three main types of user-defined functions in SQL Server: Scalar Inline Table-Valued Multi-statement Table-Valued I could also look at user-defined CLR functions, including aggregate functions, but not today. I figure that most people don’t tend to get around to doing CLR functions, and I’m going to focus on the T-SQL-based user-defined functions. Most people split these types of function up into two types. So do I. Except that most people pick them based on ‘scalar or table-valued’. I’d rather go with ‘inline or not’. If it’s not inline, it’s rubbish. It really is. Let’s start by considering the two kinds of table-valued function, and compare them. These functions are going to return the sales for a particular salesperson in a particular year, from the AdventureWorks database. CREATE FUNCTION dbo.FetchSales_inline(@salespersonid int, @orderyear int) RETURNS TABLE AS  RETURN (     SELECT e.LoginID as EmployeeLogin, o.OrderDate, o.SalesOrderID     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = @salespersonid     AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')     AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101') ) ; GO CREATE FUNCTION dbo.FetchSales_multi(@salespersonid int, @orderyear int) RETURNS @results TABLE (     EmployeeLogin nvarchar(512),     OrderDate datetime,     SalesOrderID int     ) AS BEGIN     INSERT @results (EmployeeLogin, OrderDate, SalesOrderID)     SELECT e.LoginID, o.OrderDate, o.SalesOrderID     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = @salespersonid     AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')     AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101')     ;     RETURN END ; GO You’ll notice that I’m being nice and responsible with the use of the DATEADD function, so that I have SARGability on the OrderDate filter. Regular readers will be hoping I’ll show what’s going on in the execution plans here. Here I’ve run two SELECT * queries with the “Show Actual Execution Plan” option turned on. Notice that the ‘Query cost’ of the multi-statement version is just 2% of the ‘Batch cost’. But also notice there’s trickery going on. And it’s nothing to do with that extra index that I have on the OrderDate column. Trickery. Look at it – clearly, the first plan is showing us what’s going on inside the function, but the second one isn’t. The second one is blindly running the function, and then scanning the results. There’s a Sequence operator which is calling the TVF operator, and then calling a Table Scan to get the results of that function for the SELECT operator. But surely it still has to do all the work that the first one is doing... To see what’s actually going on, let’s look at the Estimated plan. Now, we see the same plans (almost) that we saw in the Actuals, but we have an extra one – the one that was used for the TVF. Here’s where we see the inner workings of it. You’ll probably recognise the right-hand side of the TVF’s plan as looking very similar to the first plan – but it’s now being called by a stack of other operators, including an INSERT statement to be able to populate the table variable that the multi-statement TVF requires. And the cost of the TVF is 57% of the batch! But it gets worse. Let’s consider what happens if we don’t need all the columns. We’ll leave out the EmployeeLogin column. Here, we see that the inline function call has been simplified down. It doesn’t need the Employee table. The join is redundant and has been eliminated from the plan, making it even cheaper. But the multi-statement plan runs the whole thing as before, only removing the extra column when the Table Scan is performed. A multi-statement function is a lot more powerful than an inline one. An inline function can only be the result of a single sub-query. It’s essentially the same as a parameterised view, because views demonstrate this same behaviour of extracting the definition of the view and using it in the outer query. A multi-statement function is clearly more powerful because it can contain far more complex logic. But a multi-statement function isn’t really a function at all. It’s a stored procedure. It’s wrapped up like a function, but behaves like a stored procedure. It would be completely unreasonable to expect that a stored procedure could be simplified down to recognise that not all the columns might be needed, but yet this is part of the pain associated with this procedural function situation. The biggest clue that a multi-statement function is more like a stored procedure than a function is the “BEGIN” and “END” statements that surround the code. If you try to create a multi-statement function without these statements, you’ll get an error – they are very much required. When I used to present on this kind of thing, I even used to call it “The Dangers of BEGIN and END”, and yes, I’ve written about this type of thing before in a similarly-named post over at my old blog. Now how about scalar functions... Suppose we wanted a scalar function to return the count of these. CREATE FUNCTION dbo.FetchSales_scalar(@salespersonid int, @orderyear int) RETURNS int AS BEGIN     RETURN (         SELECT COUNT(*)         FROM Sales.SalesOrderHeader AS o         LEFT JOIN HumanResources.Employee AS e         ON e.EmployeeID = o.SalesPersonID         WHERE o.SalesPersonID = @salespersonid         AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')         AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101')     ); END ; GO Notice the evil words? They’re required. Try to remove them, you just get an error. That’s right – any scalar function is procedural, despite the fact that you wrap up a sub-query inside that RETURN statement. It’s as ugly as anything. Hopefully this will change in future versions. Let’s have a look at how this is reflected in an execution plan. Here’s a query, its Actual plan, and its Estimated plan: SELECT e.LoginID, y.year, dbo.FetchSales_scalar(p.SalesPersonID, y.year) AS NumSales FROM (VALUES (2001),(2002),(2003),(2004)) AS y (year) CROSS JOIN Sales.SalesPerson AS p LEFT JOIN HumanResources.Employee AS e ON e.EmployeeID = p.SalesPersonID; We see here that the cost of the scalar function is about twice that of the outer query. Nicely, the query optimizer has worked out that it doesn’t need the Employee table, but that’s a bit of a red herring here. There’s actually something way more significant going on. If I look at the properties of that UDF operator, it tells me that the Estimated Subtree Cost is 0.337999. If I just run the query SELECT dbo.FetchSales_scalar(281,2003); we see that the UDF cost is still unchanged. You see, this 0.0337999 is the cost of running the scalar function ONCE. But when we ran that query with the CROSS JOIN in it, we returned quite a few rows. 68 in fact. Could’ve been a lot more, if we’d had more salespeople or more years. And so we come to the biggest problem. This procedure (I don’t want to call it a function) is getting called 68 times – each one between twice as expensive as the outer query. And because it’s calling it in a separate context, there is even more overhead that I haven’t considered here. The cheek of it, to say that the Compute Scalar operator here costs 0%! I know a number of IT projects that could’ve used that kind of costing method, but that’s another story that I’m not going to go into here. Let’s look at a better way. Suppose our scalar function had been implemented as an inline one. Then it could have been expanded out like a sub-query. It could’ve run something like this: SELECT e.LoginID, y.year, (SELECT COUNT(*)     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = p.SalesPersonID     AND o.OrderDate >= DATEADD(year,y.year-2000,'20000101')     AND o.OrderDate < DATEADD(year,y.year-2000+1,'20000101')     ) AS NumSales FROM (VALUES (2001),(2002),(2003),(2004)) AS y (year) CROSS JOIN Sales.SalesPerson AS p LEFT JOIN HumanResources.Employee AS e ON e.EmployeeID = p.SalesPersonID; Don’t worry too much about the Scan of the SalesOrderHeader underneath a Nested Loop. If you remember from plenty of other posts on the matter, execution plans don’t push the data through. That Scan only runs once. The Index Spool sucks the data out of it and populates a structure that is used to feed the Stream Aggregate. The Index Spool operator gets called 68 times, but the Scan only once (the Number of Executions property demonstrates this). Here, the Query Optimizer has a full picture of what’s being asked, and can make the appropriate decision about how it accesses the data. It can simplify it down properly. To get this kind of behaviour from a function, we need it to be inline. But without inline scalar functions, we need to make our function be table-valued. Luckily, that’s ok. CREATE FUNCTION dbo.FetchSales_inline2(@salespersonid int, @orderyear int) RETURNS table AS RETURN (SELECT COUNT(*) as NumSales     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = @salespersonid     AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')     AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101') ); GO But we can’t use this as a scalar. Instead, we need to use it with the APPLY operator. SELECT e.LoginID, y.year, n.NumSales FROM (VALUES (2001),(2002),(2003),(2004)) AS y (year) CROSS JOIN Sales.SalesPerson AS p LEFT JOIN HumanResources.Employee AS e ON e.EmployeeID = p.SalesPersonID OUTER APPLY dbo.FetchSales_inline2(p.SalesPersonID, y.year) AS n; And now, we get the plan that we want for this query. All we’ve done is tell the function that it’s returning a table instead of a single value, and removed the BEGIN and END statements. We’ve had to name the column being returned, but what we’ve gained is an actual inline simplifiable function. And if we wanted it to return multiple columns, it could do that too. I really consider this function to be superior to the scalar function in every way. It does need to be handled differently in the outer query, but in many ways it’s a more elegant method there too. The function calls can be put amongst the FROM clause, where they can then be used in the WHERE or GROUP BY clauses without fear of calling the function multiple times (another horrible side effect of functions). So please. If you see BEGIN and END in a function, remember it’s not really a function, it’s a procedure. And then fix it. @rob_farley

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  • Basics of Join Factorization

    - by Hong Su
    We continue our series on optimizer transformations with a post that describes the Join Factorization transformation. The Join Factorization transformation was introduced in Oracle 11g Release 2 and applies to UNION ALL queries. Union all queries are commonly used in database applications, especially in data integration applications. In many scenarios the branches in a UNION All query share a common processing, i.e, refer to the same tables. In the current Oracle execution strategy, each branch of a UNION ALL query is evaluated independently, which leads to repetitive processing, including data access and join. The join factorization transformation offers an opportunity to share the common computations across the UNION ALL branches. Currently, join factorization only factorizes common references to base tables only, i.e, not views. Consider a simple example of query Q1. Q1:    select t1.c1, t2.c2    from t1, t2, t3    where t1.c1 = t2.c1 and t1.c1 > 1 and t2.c2 = 2 and t2.c2 = t3.c2   union all    select t1.c1, t2.c2    from t1, t2, t4    where t1.c1 = t2.c1 and t1.c1 > 1 and t2.c3 = t4.c3; Table t1 appears in both the branches. As does the filter predicates on t1 (t1.c1 > 1) and the join predicates involving t1 (t1.c1 = t2.c1). Nevertheless, without any transformation, the scan (and the filtering) on t1 has to be done twice, once per branch. Such a query may benefit from join factorization which can transform Q1 into Q2 as follows: Q2:    select t1.c1, VW_JF_1.item_2    from t1, (select t2.c1 item_1, t2.c2 item_2                   from t2, t3                    where t2.c2 = t3.c2 and t2.c2 = 2                                  union all                   select t2.c1 item_1, t2.c2 item_2                   from t2, t4                    where t2.c3 = t4.c3) VW_JF_1    where t1.c1 = VW_JF_1.item_1 and t1.c1 > 1; In Q2, t1 is "factorized" and thus the table scan and the filtering on t1 is done only once (it's shared). If t1 is large, then avoiding one extra scan of t1 can lead to a huge performance improvement. Another benefit of join factorization is that it can open up more join orders. Let's look at query Q3. Q3:    select *    from t5, (select t1.c1, t2.c2                  from t1, t2, t3                  where t1.c1 = t2.c1 and t1.c1 > 1 and t2.c2 = 2 and t2.c2 = t3.c2                 union all                  select t1.c1, t2.c2                  from t1, t2, t4                  where t1.c1 = t2.c1 and t1.c1 > 1 and t2.c3 = t4.c3) V;   where t5.c1 = V.c1 In Q3, view V is same as Q1. Before join factorization, t1, t2 and t3 must be joined first before they can be joined with t5. But if join factorization factorizes t1 from view V, t1 can then be joined with t5. This opens up new join orders. That being said, join factorization imposes certain join orders. For example, in Q2, t2 and t3 appear in the first branch of the UNION ALL query in view VW_JF_1. T2 must be joined with t3 before it can be joined with t1 which is outside of the VW_JF_1 view. The imposed join order may not necessarily be the best join order. For this reason, join factorization is performed under cost-based transformation framework; this means that we cost the plans with and without join factorization and choose the cheapest plan. Note that if the branches in UNION ALL have DISTINCT clauses, join factorization is not valid. For example, Q4 is NOT semantically equivalent to Q5.   Q4:     select distinct t1.*      from t1, t2      where t1.c1 = t2.c1  union all      select distinct t1.*      from t1, t2      where t1.c1 = t2.c1 Q5:    select distinct t1.*     from t1, (select t2.c1 item_1                   from t2                union all                   select t2.c1 item_1                  from t2) VW_JF_1     where t1.c1 = VW_JF_1.item_1 Q4 might return more rows than Q5. Q5's results are guaranteed to be duplicate free because of the DISTINCT key word at the top level while Q4's results might contain duplicates.   The examples given so far involve inner joins only. Join factorization is also supported in outer join, anti join and semi join. But only the right tables of outer join, anti join and semi joins can be factorized. It is not semantically correct to factorize the left table of outer join, anti join or semi join. For example, Q6 is NOT semantically equivalent to Q7. Q6:     select t1.c1, t2.c2    from t1, t2    where t1.c1 = t2.c1(+) and t2.c2 (+) = 2  union all    select t1.c1, t2.c2    from t1, t2      where t1.c1 = t2.c1(+) and t2.c2 (+) = 3 Q7:     select t1.c1, VW_JF_1.item_2    from t1, (select t2.c1 item_1, t2.c2 item_2                  from t2                  where t2.c2 = 2                union all                  select t2.c1 item_1, t2.c2 item_2                  from t2                                                                                                    where t2.c2 = 3) VW_JF_1       where t1.c1 = VW_JF_1.item_1(+)                                                                  However, the right side of an outer join can be factorized. For example, join factorization can transform Q8 to Q9 by factorizing t2, which is the right table of an outer join. Q8:    select t1.c2, t2.c2    from t1, t2      where t1.c1 = t2.c1 (+) and t1.c1 = 1 union all    select t1.c2, t2.c2    from t1, t2    where t1.c1 = t2.c1(+) and t1.c1 = 2 Q9:   select VW_JF_1.item_2, t2.c2   from t2,             (select t1.c1 item_1, t1.c2 item_2            from t1            where t1.c1 = 1           union all            select t1.c1 item_1, t1.c2 item_2            from t1            where t1.c1 = 2) VW_JF_1   where VW_JF_1.item_1 = t2.c1(+) All of the examples in this blog show factorizing a single table from two branches. This is just for ease of illustration. Join factorization can factorize multiple tables and from more than two UNION ALL branches.  SummaryJoin factorization is a cost-based transformation. It can factorize common computations from branches in a UNION ALL query which can lead to huge performance improvement. 

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  • What is Inversion of control and why we need it?

    - by Jalpesh P. Vadgama
    Most of programmer need inversion of control pattern in today’s complex real time application world. So I have decided to write a blog post about it. This blog post will explain what is Inversion of control and why we need it. We are going to take a real world example so it would be better to understand. The problem- Why we need inversion of control? Before giving definition of Inversion of control let’s take a simple real word example to see why we need inversion of control. Please have look on the following code. public class class1 { private class2 _class2; public class1() { _class2=new class2(); } } public class class2 { //Some implementation of class2 } I have two classes “Class1” and “Class2”.  If you see the code in that I have created a instance of class2 class in the class1 class constructor. So the “class1” class is dependent on “class2”. I think that is the biggest issue in real world scenario as if we change the “class2” class then we might need to change the “class1” class also. Here there is one type of dependency between this two classes that is called Tight Coupling. Tight coupling will have lots of problem in real world applications as things are tends to be change in future so we have to change all the tight couple classes that are dependent of each other. To avoid this kind of issue we need Inversion of control. What is Inversion of Control? According to the wikipedia following is a definition of Inversion of control. “In software engineering, Inversion of Control (IoC) is an object-oriented programming practice where the object coupling is bound at run time by an assembler object and is typically not known at compile time using static analysis.” So if you read the it carefully it says that we should have object coupling at run time not compile time where it know what object it will create, what method it will call or what feature it will going to use for that. We need to use same classes in such way so that it will not tight couple with each other. There are multiple way to implement Inversion of control. You can refer wikipedia link for knowing multiple ways of implementing Inversion of control. In future posts we are going to see all the different way of implementing Inversion of control.

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