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  • Using set operation in LINQ

    - by vik20000in
    There are many set operation that are required to be performed while working with any kind of data. This can be done very easily with the help of LINQ methods available for this functionality. Below are some of the examples of the set operation with LINQ. Finding distinct values in the set of data. We can use the distinct method to find out distinct values in a given list.     int[] factorsOf300 = { 2, 2, 3, 5, 5 };     var uniqueFactors = factorsOf300.Distinct(); We can also use the set operation of UNION with the help of UNION method in the LINQ. The Union method takes another collection as a parameter and returns the distinct union values in  both the list. Below is an example.     int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };    int[] numbersB = { 1, 3, 5, 7, 8 };    var uniqueNumbers = numbersA.Union(numbersB); We can also get the set operation of INTERSECT with the help of the INTERSECT method. Below is an example.     int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };     int[] numbersB = { 1, 3, 5, 7, 8 };         var commonNumbers = numbersA.Intersect(numbersB);  We can also find the difference between the 2 sets of data with the help of except method.      int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };     int[] numbersB = { 1, 3, 5, 7, 8 };         IEnumerable<int> aOnlyNumbers = numbersA.Except(numbersB);  Vikram

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  • Linq to SQL Lazy Loading in ASP.Net applications

    - by nikolaosk
    In this post I would like to talk about LINQ to SQL and its native lazy loading functionality. I will show you how you can change this behavior. We will create a simple ASP.Net application to demonstrate this. I have seen a lot of people struggling with performance issues. That is mostly due to the lack of knowledge of how LINQ internally works.Imagine that we have two tables Products and Suppliers (Northwind database). There is one to many relationship between those tables-entities. One supplier...(read more)

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  • Inheritance Mapping Strategies with Entity Framework Code First CTP5: Part 2 – Table per Type (TPT)

    - by mortezam
    In the previous blog post you saw that there are three different approaches to representing an inheritance hierarchy and I explained Table per Hierarchy (TPH) as the default mapping strategy in EF Code First. We argued that the disadvantages of TPH may be too serious for our design since it results in denormalized schemas that can become a major burden in the long run. In today’s blog post we are going to learn about Table per Type (TPT) as another inheritance mapping strategy and we'll see that TPT doesn’t expose us to this problem. Table per Type (TPT)Table per Type is about representing inheritance relationships as relational foreign key associations. Every class/subclass that declares persistent properties—including abstract classes—has its own table. The table for subclasses contains columns only for each noninherited property (each property declared by the subclass itself) along with a primary key that is also a foreign key of the base class table. This approach is shown in the following figure: For example, if an instance of the CreditCard subclass is made persistent, the values of properties declared by the BillingDetail base class are persisted to a new row of the BillingDetails table. Only the values of properties declared by the subclass (i.e. CreditCard) are persisted to a new row of the CreditCards table. The two rows are linked together by their shared primary key value. Later, the subclass instance may be retrieved from the database by joining the subclass table with the base class table. TPT Advantages The primary advantage of this strategy is that the SQL schema is normalized. In addition, schema evolution is straightforward (modifying the base class or adding a new subclass is just a matter of modify/add one table). Integrity constraint definition are also straightforward (note how CardType in CreditCards table is now a non-nullable column). Another much more important advantage is the ability to handle polymorphic associations (a polymorphic association is an association to a base class, hence to all classes in the hierarchy with dynamic resolution of the concrete class at runtime). A polymorphic association to a particular subclass may be represented as a foreign key referencing the table of that particular subclass. Implement TPT in EF Code First We can create a TPT mapping simply by placing Table attribute on the subclasses to specify the mapped table name (Table attribute is a new data annotation and has been added to System.ComponentModel.DataAnnotations namespace in CTP5): public abstract class BillingDetail {     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } } [Table("BankAccounts")] public class BankAccount : BillingDetail {     public string BankName { get; set; }     public string Swift { get; set; } } [Table("CreditCards")] 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; } } If you prefer fluent API, then you can create a TPT mapping by using ToTable() method: protected override void OnModelCreating(ModelBuilder modelBuilder) {     modelBuilder.Entity<BankAccount>().ToTable("BankAccounts");     modelBuilder.Entity<CreditCard>().ToTable("CreditCards"); } Generated SQL For QueriesLet’s take an example of a simple non-polymorphic query that returns a list of all the BankAccounts: var query = from b in context.BillingDetails.OfType<BankAccount>() select b; Executing this query (by invoking ToList() method) results in the following SQL statements being sent to the database (on the bottom, you can also see the result of executing the generated query in SQL Server Management Studio): Now, let’s take an example of a very simple polymorphic query that requests all the BillingDetails which includes both BankAccount and CreditCard types: projects some properties out of the base class BillingDetail, without querying for anything from any of the subclasses: var query = from b in context.BillingDetails             select new { b.BillingDetailId, b.Number, b.Owner }; -- var query = from b in context.BillingDetails select b; This LINQ query seems even more simple than the previous one but the resulting SQL query is not as simple as you might expect: -- As you can see, EF Code First relies on an INNER JOIN to detect the existence (or absence) of rows in the subclass tables CreditCards and BankAccounts so it can determine the concrete subclass for a particular row of the BillingDetails table. Also the SQL CASE statements that you see in the beginning of the query is just to ensure columns that are irrelevant for a particular row have NULL values in the returning flattened table. (e.g. BankName for a row that represents a CreditCard type) TPT ConsiderationsEven though this mapping strategy is deceptively simple, the experience shows that performance can be unacceptable for complex class hierarchies because queries always require a join across many tables. In addition, this mapping strategy is more difficult to implement by hand— even ad-hoc reporting is more complex. This is an important consideration if you plan to use handwritten SQL in your application (For ad hoc reporting, database views provide a way to offset the complexity of the TPT strategy. A view may be used to transform the table-per-type model into the much simpler table-per-hierarchy model.) SummaryIn this post we learned about Table per Type as the second inheritance mapping in our series. So far, the strategies we’ve discussed require extra consideration with regard to the SQL schema (e.g. in TPT, foreign keys are needed). This situation changes with the Table per Concrete Type (TPC) that we will discuss in the next post. 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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  • Flattening a Jagged Array with LINQ

    - by PSteele
    Today I had to flatten a jagged array.  In my case, it was a string[][] and I needed to make sure every single string contained in that jagged array was set to something (non-null and non-empty).  LINQ made the flattening very easy.  In fact, I ended up making a generic version that I could use to flatten any type of jagged array (assuming it's a T[][]): private static IEnumerable<T> Flatten<T>(IEnumerable<T[]> data) { return from r in data from c in r select c; } Then, checking to make sure the data was valid, was easy: var flattened = Flatten(data); bool isValid = !flattened.Any(s => String.IsNullOrEmpty(s)); You could even use method grouping and reduce the validation to: bool isValid = !flattened.Any(String.IsNullOrEmpty); Technorati Tags: .NET,LINQ,Jagged Array

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  • LINQ Style preference

    - by Erin
    I have come to use LINQ in my every day programming a lot. In fact, I rarely, if ever, use an explicit loop. I have, however, found that I don't use the SQL like syntax anymore. I just use the extension functions. So rather then saying: from x in y select datatransform where filter I use: x.Where(c => filter).Select(c => datatransform) Which style of LINQ do you prefer and what are others on your team are comfortable with?

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  • How to profile LINQ to Entities queries in your asp.net applications - part 3

    - by nikolaosk
    In this post I will continue exploring ways on how to profile database activity when using the Entity Framework as the data access layer in our applications. If you want to read the first post of the series click here . If you want to read the second post of the series click here . In this post I will use the excellent (best tool for EF profiling) which is called Entity Framework Profiler. You can download the trial - fully functional edition of this tool from here . I will use the previous example...(read more)

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  • How to profile LINQ to Entities queries in your asp.net applications - part 2

    - by nikolaosk
    In this post I will continue exploring ways on how to profile database activity when using the Entity Framework as the data access layer in our applications. I will use a simple asp.net web site and EF to demonstrate this. If you want to read the first post of the series click here . In this post I will use the Tracing Provider Wrappers which extend the Entity framework. You can download the whole solutions/samples project from here .The providers were developed from Jaroslaw Kowalski . 1) Unzip...(read more)

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  • OrderBy and Distinct using LINQ-to-Entities

    - by BlueRaja
    Here is my LINQ query: (from o in entities.MyTable orderby o.MyColumn select o.MyColumn).Distinct(); Here is the result: {"a", "c", "b", "d"} Here is the generated SQL: SELECT [Distinct1].[MyColumn] AS [MyColumn] FROM ( SELECT DISTINCT [Extent1].[MyColumn] AS [MyColumn] FROM [dbo].[MyTable] AS [Extent1] ) AS [Distinct1] Is this a bug? Where's my ordering, damnit?

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  • Concatenate int and string in LINQ

    - by Waheed
    HI, I am using the following code from c in Country where c.IsActive.Equals(true) orderby c.CountryName select new { countryIDCode = c.CountryID + "|" + c.TwoDigitCode, countryName = c.CountryName } but following is the error while doing this... Unable to cast the type 'System.Int32' to type 'System.Object'. LINQ to Entities only supports casting Entity Data Model primitive types. CountryID is int type and TwoDigitCode is string type. Can u please let me know how to concatenate.... Thanks....

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  • Cross-table linq query with EF4/POCO

    - by Basiclife
    Hi All, I'm new to EF(any version) and POCO. I'm trying to use POCO entities with a generic repository in a "code-first" mode(?) I've got some POCO Entities (no proxies, no lazy loading, nothing). I have a repository(of T as Entity) which provides me with basic get/getsingle/getfirst functionality which takes a lambda as a parameter (specifically a System.Func(Of T, Boolean)) Now as I'm returning the simplest possible POCO object, none of the relationship parameters work once they've been retrieved from the database (as I would expect). However, I had assumed (wrongly) that my lambda query passed to the repository would be able to use the links between entities as it would be executed against the DB before the simple POCO entities are generated. The flow is: GUI calls: Public Function GetAllTypesForCategory(ByVal CategoryID As Guid) As IEnumerable(Of ItemType) Return ItemTypeRepository.Get(Function(x) x.Category.ID = CategoryID) End Function Get is defined in Repository(of T as Entity): Public Function [Get](ByVal Query As System.Func(Of T, Boolean)) As IEnumerable(Of T) Implements Interfaces.IRepository(Of T).Get Return ObjectSet.Where(Query).ToList() End Function The code doesn't error when this method is called but does when I try to use the result set. (This seems to be a lazy loading behaviour so I tried adding the .ToList() to force eager loading - no difference) I'm using unity/IOC to wire it all up but I believe that's irrelevant to the issue I'm having NB: Relationships between entities are being configured properly and if I turn on proxies/lazy loading/etc... this all just works. I'm intentionally leaving all that turned off as some calls to the BL will be from a website but some will be via WCF - So I want the simplest possible objects. Also, I don't want a change in an object passed to the UI to be committed to the DB if another BL method calls Commit() Can someone please either point out how to make this work or explain why it's not possible? All I want to do is make sure the lambda I pass in is performed against the DB before the results are returned Many thanks. In case it matters, the container is being populated with everything as shown below: Container.AddNewExtension(Of EFRepositoryExtension)() Container.Configure(Of IEFRepositoryExtension)(). WithConnection(ConnectionString). WithContextLifetime(New HttpContextLifetimeManager(Of IObjectContext)()). ConfigureEntity(New CategoryConfig(), "Categories"). ConfigureEntity(New ItemConfig()). ... )

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  • deploying applications that use LINQ to Entities.

    - by Luiscencio
    HI COMUNITY!!!! I want to use L2E since it s very convenient to my company's apps, I created a demo project, the demo does run on every machine but when I, lets say, press a button that has some code that uses the entity I get this error: specified store provider cannot be found in the configuration, or is not valid. note that I get this error only on machines that does not have VS2008 installed, on these machines (the ones with VS2008) the demo works well. any advice is appreciated.

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  • LINQ to SQL get grouped MIN with JOIN

    - by Ira Rainey
    I'm having trouble with a LINQ to SQL query getting the min value using Visual Basic. Here's the SQL: SELECT RC.AssetID, MIN(RC.RecCode) AS RecCode, JA.EngineerNote from JobAssetRecCode RC JOIN JobAssets JA ON JA.AssetID = RC.AssetID AND JA.JobID = RC.JobID WHERE RC.InspState = 2 AND RC.RecCode > 0 AND RC.JobID = @JobID GROUP BY RC.AssetID, JA.EngineerNote; I seem to be going around in circles here with grouping etc not managing to get it working. Any help would be greatly appreciated.

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  • LINQ to SQL select distinct from multiple colums

    - by Morron
    Hi, I'm using LINQ to SQL to select some columns from one table. I want to get rid of the duplicate result also. Dim customer = (From cus In db.Customers Select cus.CustomerId, cus.CustomerName).Distinct Result: 1 David 2 James 1 David 3 Smith 2 James 5 Joe Wanted result: 1 David 2 James 3 Smith 5 Joe Can anyone show me how to get the wanted result? Thanks.

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  • Using linq to combine objects

    - by DotnetDude
    I have 2 instances of a class that implements the IEnumerable interface. I would like to create a new object and combine both of them into one. I understand I can use the for..each to do this. Is there a linq/lambda expression way of doing this?

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  • Updating multiple tables at the same time in Linq-to-SQL

    - by kiran
    How do I update two tables at the same time using Linq-to-SQL? var z = from a in db.Products join b in db.ProductSubcategories on a.ProductSubcategoryID equals b.ProductSubcategoryID join d in db.ProductCategories on b.ProductCategoryID equals d.ProductCategoryID select new { ProductName = a.Name, ProductCategory = d.Name, ProductSubCategory = b.Name, Cost = a.StandardCost, discontinuedDate = a.DiscontinuedDate, ProductId=a.ProductID };

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  • Dynamic LINQ OrderBy

    - by John Sheehan
    I found an example in the VS2008 Examples for Dynamic LINQ that allows you to use a sql-like string (e.g. OrderBy("Name, Age DESC")) for ordering. Unfortunately, the method included only works on IQueryable<T>. Is there any way to get this functionality on IEnumerable<T>?

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  • c# linq to xml dynamic query

    - by David Archer
    Right, bit of a strange question; I have been doing some linq to XML work recently (see my other recent posts here and here). Basically, I want to be able to create a query that checks whether a textbox is null before it's value is included in the query, like so: XDocument db = XDocument.Load(xmlPath); var query = (from vals in db.Descendants("Customer") where (if(textbox1.Text != "") {vals.Element("CustomerID") == Convert.ToInt32(textbox1.Text) } || if(textbox2.Text != "") {vals.Element("Name") == textbox2.Text}) select vals).ToList();

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  • Linq-to-SQL: How to perform a count on a sub-select

    - by Peter Bridger
    I'm still trying to get my head round how to use LINQ-to-SQL correctly, rather than just writing my own sprocs. In the code belong a userId is passed into the method, then LINQ uses this to get all rows from the GroupTable tables matching the userId. The primary key of the GroupUser table is GroupUserId, which is a foreign key in the Group table. /// <summary> /// Return summary details about the groups a user belongs to /// </summary> /// <param name="userId"></param> /// <returns></returns> public List<Group> GroupsForUser(int userId) { DataAccess.KINv2DataContext db = new DataAccess.KINv2DataContext(); List<Group> groups = new List<Group>(); groups = (from g in db.Groups join gu in db.GroupUsers on g.GroupId equals gu.GroupId where g.Active == true && gu.UserId == userId select new Group { Name = g.Name, CreatedOn = g.CreatedOn }).ToList<Group>(); return groups; } } This works fine, but I'd also like to return the total number of Users who are in a group and also the total number of Contacts that fall under ownership of the group. Pseudo code ahoy! /// <summary> /// Return summary details about the groups a user belongs to /// </summary> /// <param name="userId"></param> /// <returns></returns> public List<Group> GroupsForUser(int userId) { DataAccess.KINv2DataContext db = new DataAccess.KINv2DataContext(); List<Group> groups = new List<Group>(); groups = (from g in db.Groups join gu in db.GroupUsers on g.GroupId equals gu.GroupId where g.Active == true && gu.UserId == userId select new Group { Name = g.Name, CreatedOn = g.CreatedOn, // ### This is the SQL I would write to get the data I want ### MemberCount = ( SELECT COUNT(*) FROM GroupUser AS GU WHERE GU.GroupId = g.GroupId ), ContactCount = ( SELECT COUNT(*) FROM Contact AS C WHERE C.OwnerGroupId = g.GroupId ) // ### End of extra code ### }).ToList<Group>(); return groups; } }

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  • Load parent and child table in one query linq to entitiy

    - by parminder
    Hi Experts, I have a following tables/classes structure in Linq to entities. ` Books { bookId, Title } Tags { TagId Tag } BooksTags { BookId TagId } ' Now I need to write a query which gives me result like this Class Result { bookId, Title Tags } Tags should be comma separated text from the tags table by joining all three tables. How to get it done. Thanks Parminder

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  • Get sum of two columns in one LINQ query

    - by Axarydax
    Hi, let's say that I have a table called Items (ID int, Done int, Total int) I can do it by two queries: int total = m.Items.Sum(p=>p.Total) int done = m.Items.Sum(p=>p.Done) But I'd like to do it in one query, something like this: var x = from p in m.Items select new { Sum(p.Total), Sum(p.Done)}; Surely there is a way to call aggregate functions from LINQ syntax...?

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  • Convert this Linq query from query syntax to lambda expression

    - by Jinkinz
    I'm not sure I like linq query syntax...its just not my preference. But I don't know what this query would look like using lambda expressions, can someone help? from securityRoles in user.SecurityRoles from permissions in securityRoles.Permissions where permissions.SecurableEntity.Name == "Unit" && permissions.PermissionType.Name == "Read" orderby permissions.PermissionLevel.Value descending select permissions There is a many-to-many relationship between users and security roles that makes this extra confusing. Thanks! Kelly

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  • sql to xml using linq - nested collections

    - by nelsonwebs
    I have a table of data that looks something like this. name, hour, price1, price2, price3, price4, price5 fred, 3, 12.5, 13.5, 14, 15, 16 dave, 6, 8, 12, 18, 20.2, 25 fred, 6, 10, 11, 14, 15, 19.7 This table needs to be output to an xml file that looks like this. <timeCost> <person name="fred"> <time hour="5"> <cost price="12.5" /> <cost price="13.5" /> <cost price="14" /> <cost price="15" /> <cost price="16" /> </time> <time hour="6"> <cost price="10" /> <cost price="11" /> <cost price="14" /> <cost price="15" /> <cost price="19.7" /> </time> </person> <person name="dave"> <time hour="6"> <cost price="8" /> <cost price="12" /> <cost price="18" /> <cost price="20.2" /> <cost price="25" /> </time> </person> </timeCost> I have a linq query to get the data from SQL something like this. // initialize data context var people = from p in dc.people orderby p.name, p.hour select p; However, I'm having trouble writing the xml out using linq (csharp). Specifically, the problem is I don't know how to deal with having multiple time nodes under each name node (nested loops/collections). How can this be done? This is a sql 08 ent db if it matters to anyone.

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  • LINQ: Create persistable Associations in Code, Without Foreign Key

    - by Alex
    Hello, I know that I can create LINQ Associations without a Foreign Key. The problem is, I've been doing this by adding the [Association] attribute in the DBML file (same as through the designer), which will get erased again after I refresh my database (and reload the entire table structure). I know that there is the MyData.cs file (as part of the DBML) in which I can place my partial extensions etc. to domain objects (to persist even after I refresh the DBML), but I don't know how to create an association there?

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