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• Accessing non-related entities in LinqToSql entity classes

  - by Chris Johnson

  In LinqToSql, if I want to access a non-related entity in an entity partial class, how do I do this without creating a new DataContext? Here's the scenario: I have the tables Client, IssueType and ClientIssueType. A Client may specify a list of IssueTypes if they do not want to use the default IssueTypes. I have the default IssueTypes in the ClientIssueType table with a ClientId of null. In my Client partial I'd like to try to retrieve all IssueTypes, and if none are found, return all default IssueTypes. The only way I can see of accessing the IssueTypes with a null ClientId is by accessing the table through a new DataContext, which is problematic once I want to start assigning them to Issues. Where am I going wrong?

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• ASP.net MVC3 entities, don't know how to count

  - by Spedax

  I have 2 tables, 1 with countries, 1 with states. The states table has a column with Population. I'm using entities and I have created a List of states for the countries public class TblCountries { //Entities for my table country ... public List<tblStates> States { get; set; } } So now I can for example List all the states that belong to a country. Now what I want to do is count the population, so I can show the population that of an entire country. I tried using in my view @foreach (var item in Model.Countries) { @Html.DisplayFor(modelItem => item.States.Count<population>) } But this doesn't work, anyone know how to do this? Thanks in advanced!

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• Handling duplicate insertion

  - by Francis

  So I've got this piece of code which, logically should work but Entity Framework is behaving unexpectedly. Here: foreach (SomeClass someobject in allObjects) { Supplier supplier = new Supplier(); supplier.primary_key = someobject.id; supplier.name = someobject.displayname; try { sm.Add(supplier); ro.Created++; } catch (Exception ex) { ro.Error++; } } Here's what I have in sm.Add() public Supplier Add(Supplier supplier) { try { _ctx.AddToSupplier(supplier); _ctx.SaveChanges(); return supplier; } catch (Exception ex) { throw; } } I can have records in allObjects that have the same id. My piece of code needs to support this and just move on to the next and try to insert it, which I think should work. If this happens, an exception is throw, saying that records with dupe PKs cannot be inserted (of course). The exception mentions the value of the PK, for example 1000. All is well, a new supplier is passed to sm.Add() containing a PK that's never been used before. (1001) Weirdly though, when doing SaveChanges(), EF will whine about not being able to insert records with dupe PKs. The exception still mentions 1000 even though supplier contains 10001 in primary_key. I feel this is me not using _ctx properly. Do I need to call something else to sync it ?

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• Does Distinct() preserve always take the first element in the list

  - by Cornelius

  Would int[] nums = { 2, 3, 3, 4, 2, 1, 6, 7, 10 }; var distinct = nums.Distinct(); always return 2, 3, 4, 1, 6, 7, 10 in that order?

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• Reactive Extensions for Java

  - by Timo Westkämper

  Is there any equivalent of Reactive Extensions (.NET) for Java? About Rx (Reactive Extensions) Rx is a library for composing asynchronous and event-based programs using observable collections. I am aware of rule engines such as Drools from JBOSS, but is there some other way that is closer to the Microsoft .NET approach?

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• building list of child objects inside main object

  - by Asdfg

  I have two tables like this: Category: Id Name ------------------ 1 Cat1 2 Cat2 Feature: Id Name CategoryId -------------------------------- 1 F1 1 2 F2 1 3 F3 2 4 F4 2 5 F5 2 In my .Net classes, i have two POCO classes like this: public class Category { public int Id {get;set;} public int Name {get;set;} public IList<Feature> Features {get;set;} } public class Feature { public int Id {get;set;} public int CategoryId {get;set;} public int Name {get;set;} } I am using a stored proc that returns me a result set by joining these 2 tables. This is how my Stored Proc returns the result set. SELECT c.CategoryId, c.Name Category, f.FeatureId, f.Name Feature FROM Category c INNER JOIN Feature f ON c.CategoryId = f.CategoryId ORDER BY c.Name --Resultset produced by the above query CategoryId CategoryName FeatureId FeatureName --------------------------------------------------- 1 Cat1 1 F1 1 Cat1 2 F2 2 Cat2 3 F3 2 Cat2 4 F4 2 Cat2 5 F5 Now if i want to build the list of categories in my .Net code, i have to loop thru the result set and add features unless the category changes. This is how my .Net code looks like that builds Categories and Features. List<Category> categories = new List<Category>(); Int32 lastCategoryId = 0; Category c = new Category(); using (SqlDataReader reader = cmd.ExecuteReader()) { while (reader.Read()) { //Check if the categoryid is same as previous one. //If Not, add new category. //If Yes, dont add the category. if (lastCategoryId != Convert.ToInt32(reader["CategoryId"])) { c = new Category { Id = Convert.ToInt32(reader["CategoryId"]), Name = reader["CategoryName"].ToString() }; c.Features = new List<Feature>(); categories.Add(c); } lastCategoryId = Convert.ToInt32(reader["CategoryId"]); //Add Feature c.Features.Add(new Feature { Name = reader["FeatureName"].ToString(), Id = Convert.ToInt32(reader["FeatureId"]) }); } return categories; } I was wondering if there is a better way to do build the list of Categories?

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• how to populate an entity you have extended in the Entity Framework?

  - by user169867

  I have an entity in my EDMX that I've extended with a few fields in a partial class like this: public partial class Employee { public string JobName {get;set;} } These properties are for display only. In the above example say the entity has a JobTypeID property. I wish JobName to be populated w/ the name that belongs to that JobTypeID. Is there anyway to query the employee record in EF including the value for the JobName property w/o explicity assigning each field using select()? The reason I ask is that there are a lot of fields in the Employee entity so I'd like to be able to take advantage of something like: ctx.Employees.Where(e=>e.EmployeeID==employeeID).Single() ...add somehow fill in JobName too Is this possible?

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• Column.DbType affecting runtime behavior

  - by leppie

  Hi According to the MSDN docs, the DbType property/attribute of a Column type/element is only used for database creation. Yet, today, when trying to submit data to an IMAGE column on a SQLCE database (not sure if only on CE), I got an exception of 'Data truncated to 8000 bytes'. This was due to the DbType still being defined as VARBINARY(MAX) which SQLCE does not support. Changing the type to IMAGE in the DbType fixes the issue. So what other surprises does Linq2SQL attributes hold in store? Is this a bug or intended? Should I report it to MS? UPDATE After getting the answer from Guffa, I tested it, but it seems for NVARCHAR(10) adding a 11 char length string causes a SQL exception, and not Linq2SQL one. The data was truncated while converting from one data type to another. [ Name of function(if known) = ] A first chance exception of type 'System.Data.SqlServerCe.SqlCeException' occurred in System.Data.SqlServerCe.dll

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• Updating Many-to-Many relationship with LinqToSQL

  - by Noffie

  If I had, for example, a Many-to-Many mapping table called "RolesToUsers" between a Users and an Roles table, here is how I do it: // DataContext is db, usr is a User entity // newUserRolesMappings is a collection with the desired new mappings, probably // derived by looking at selections in a checkbox list of Roles on a User Edit page db.RolesToUsers.DeleteAllOnSubmit(usr.RolesToUsers); usr.RolesToUsers.Clear(); usr.RolesToUsers.AddRange(newUserRolesMappings); I used the SQL profiler once, and this seems to generate very intelligent SQL - it will only drop the rows which are no longer in the mapping relationship, and only add rows which did not already exist in the relationship. It doesn't blindly do a complete clearing and re-construction of the relationship, as I thought it would. The internet is surprisingly quiet on the subject, and the query "LinqToSQL many-to-many" mostly just turns up articles about how the LinqToSQL data mapper doesn't "support" it very well. How does everyone else update many-to-many with LinqToSQL?

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• L2S, what's better

  - by msony

  db.Albums.FirstOrDefault(x => x.OrderId == order) or db.Albums.FirstOrDefault(x => x.OrderId.Equals(order))

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• Interview Question: .Any() vs if (.Length > 0) for testing if a collection has elements

  - by Chris

  In a recent interview I was asked what the difference between .Any() and .Length > 0 was and why I would use either when testing to see if a collection had elements. This threw me a little as it seems a little obvious but feel I may be missing something. I suggested that you use .Length when you simply need to know that a collection has elements and .Any() when you wish to filter the results. Presumably .Any() takes a performance hit too as it has to do a loop / query internally.

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• How can i mock or test my deferred execution functionality?

  - by cottsak

  I have what could be seen as a bizarre hybrid of IQueryable<T> and IList<T> collections of domain objects passed up my application stack. I'm trying to maintain as much of the 'late querying' or 'lazy loading' as possible. I do this in two ways: By using a LinqToSql data layer and passing IQueryable<T>s through by repositories and to my app layer. Then after my app layer passing IList<T>s but where certain elements in the object/aggregate graph are 'chained' with delegates so as to defer their loading. Sometimes even the delegate contents rely on IQueryable<T> sources and the DataContext are injected. This works for me so far. What is blindingly difficult is proving that this design actually works. Ie. If i defeat the 'lazy' part somewhere and my execution happens early then the whole thing is a waste of time. I'd like to be able to TDD this somehow. I don't know a lot about delegates or thread safety as it applies to delegates acting on the same source. I'd like to be able to mock the DataContext and somehow trace both methods of deferring (IQueryable<T>'s SQL and the delegates) the loading so that i can have tests that prove that both functions are working at different levels/layers of the app/stack. As it's crucial that the deferring works for the design to be of any value, i'd like to see tests fail when i break the design at a given level (separate from the live implementation). Is this possible?

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• Compiled query using list of class objects in C#

  - by Sukan

  Hello , Can somebody help me out in creating compiled queries where input is to be a list of class objects? I have seen examples where Func<DataContext, somematchobject, IQueryable<T>> is created and compiled. But can I do something like Func<List<T>, matchObject, T>, and compile it? Basically I want an object(T) meeting certain conditions (as in matchObject) to be returned from a list of objects(List<T>). Will CompiledQuery.Compile help me in this? Please help me experts!!

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• How to Solve this Error "Cannot convert lambda expression to type 'string' because it is not a deleg

  - by peace

  . I get this error: "Cannot convert lambda expression to type 'string' because it is not a delegate type" - keyword select become underlined in blue Can you please advice. Employee emp = new Employee(); comHandledBySQt.DataSource = from x in emp.GetDataFromTable("1") select new { x.Id, Name = x.FirstName + " " + x.LastName }; comHandledBySQt.DisplayMember = "Name"; comHandledBySQt.ValueMember = "Id"; Above code should displays drop list of employees first name and last name in a combo box

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• Linq2Sql How to write outer join query?

  - by Malcolm

  Hi, I have following SQL tables. ImportantMessages impID Message ImportantMessageUsers imuID imuUserID imuImpID I want to write a Linq2Sql query so that it returns any rows from ImportantMessages that does not have a record in ImportantMessagesUsers. Matchiing fields are impID ----- imuImpID Assume imuUserID of 6

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• association of more than one model to a listview

  - by Veer

  I have 3 Tables in my database. Each table has 3 fields each, excluding the ID field. out of which 2 fields are of type nvarchar. None of the tables are related. My ListView in the application helps the user to search my database, the search being incremental. The search includes the nvarchar fields of the 3 tables ie, 6 fields in total. Eg: PhoneBook: Name, PhoneNo Notes: Title, Content Bookmarks: Name, url I've the models generated for the 3 tables. Now the ListBox should display the Ph.Name, Title and the Bo.Name fields. ie, It should be bound to them. But they are from different models. I also should be able to perform CRUD operation on the item searched. How would i do that? P.S: Separate ViewModels are created for each Model which are used for their respective views for handling those tables individually. But this is an integrated view where the user should be able to search everything. Also please somebody suggest me a better Title for this question:)

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• Updating an object with L2S with ASP.NET MVC

  - by Paul

  Is there an easier way to update an object with L2S other then doing it property by property? This is what I am doing now: Public ActionResult Edit(Object obj) { var objToUpdate = _repository.Single<Object>(o => o.id = obj.id); objToUpdate.Prop1 = obj.Prob1; objToUpdate.Prop2 = obj.Prop2; ... _repository.SubmitChanges(); } I am hoping there is a way to just say objToUpdate = obj then submit the changes??? Any help on this would be appreciated!

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• Why can't you return a List from a Compiled Query?

  - by Andrew

  I was speeding up my app by using compiled queries for queries which were getting hit over and over. I tried to implement it like this: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id) End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, List(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ (From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u).ToList()) This did not work and I got this error message: Type : System.ArgumentNullException, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 Message : Value cannot be null. Parameter name: value However, when I changed my compiled query to return IQueryable instead of List like so: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id).ToList() End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, IQueryable(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u) It worked fine. Can anyone shed any light as to why this is? BTW, compiled queries rock! They sped up my app by a factor of 2.

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• Beginner Question on traversing a EF4 model

  - by user564577

  I have a basic EF4 model with two entities. I'm using Self Tracking Entities Client has ClientAddresses relationship on clientkey = clientkey. (1 to many) How do i get a list/collection of client entities (STE) and their addresses (STE) but only ones where they live in a particular state or some such filter on the address??? This seems to filter and bring back clients but doesnt bring back addresses. var j = from client in context.Clients where client.ClientAddresses.All(c => c.ZIP == "80923") select client; I cant get this to create the Addresses because ClientAddresses is IEnumerable and it needs a TrackableCollection var query = from t1 in context.Clients join t2 in context.ClientAddresses on t1.ClientKey equals t2.ClientKey where t2.ZIP == "80923" select new Client { FirstName = t1.FirstName, LastName = t1.LastName, IsEnabled = t1.IsEnabled, ClientKey = t1.ClientKey, ChangeUser = t1.ChangeUser, ChangeDate = t1.ChangeDate, ClientAddresses = from a in t1.ClientAddresses select new ClientAddress { AddressKey = a.AddressKey, AddressLine1 = a.AddressLine1, AddressLine2 = a.AddressLine2, AddressTypeCode = a.AddressTypeCode, City = a.City, ClientKey = a.ClientKey, State = a.State, ZIP = a.ZIP } }; Any pointers would be appreciated. Thanks Edit: This seems to work.... var j = from client in context.Clients.Include("ClientAddresses") where client.ClientAddresses.Any(c => c.ZIP == "80923") select client;

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• Generate Numbers and Select in memory

  - by Jasl

  I want to do the following dynamically Generate numbers from 1 to 100 and then select 25 random numbers from it and display it in a console. Any easy way to do so?

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• L2S DataContext out of synch: row not found or changed

  - by awrigley

  The Problem I am getting a number of errors that imply that the DataContext, or rather, the way I am using the DataContext is getting out of synch. The error occurs on db.SubmitChanges() where db is my DataContext instance. The error is: Row not found or changed. The problem only occurs intermitently, for example, adding a row then deleting it. If I stop the dev server and restart, the added row is there and I can delete it no problem. Ie, it seems that the problem is related to the DataContext losing track of the rows that have been added. IMPORTANT: Before anyone votes to close this thread, on the basis of it being a duplicate, I have checked the sql server profiler and there is no "Where 0 = 1" in the SQL. I have also recreated the dbml file, so am satisfied that the database schema is in synch with the schema represented by the dbml file. Ie, no cases of mismatched nullable/not nullable columns, etc. My Diagnosis (for what it is worth): It seems to be a problem related to how I am using the DataContext. I am new to MVC, Repositories and Services patterns, so suspect that I have wired things up wrong. The Setup Simple eLearning app in its early stages. Pupils need to be able to add and delete courses (Courses table) to their UserCourses. To do this, I have a service that gets a specific DataContext instance Dependency Injected into its constructor. Service Class Constructor: public class SqlPupilBlockService : IPupilBlockService { DataContext db; public SqlPupilBlockService(DataContext db) { this.db = db; CoursesRepository = new SqlRepository<Course>(db); UserCoursesRepository = new SqlRepository<UserCourse>(db); } // Etc, etc } The CoursesRepository and UserCoursesRepository are both private properties of the service class that are of Type IRepository (just a simple generic repository interface). Sql Respoitory Code: public class SqlRepository<T> : IRepository<T> where T : class { DataContext db; public SqlRepository(DataContext db) { this.db = db; } #region IRepository<T> Members public IQueryable<T> Query { get { return db.GetTable<T>(); } } public List<T> FetchAll() { return Query.ToList(); } public void Add(T entity) { db.GetTable<T>().InsertOnSubmit(entity); } public void Delete(T entity) { db.GetTable<T>().DeleteOnSubmit(entity); } public void Save() { db.SubmitChanges(); } #endregion } The two methods for adding and deleting UserCourses are: Service Methods for Adding and Deleting UserCourses: public void AddUserCourse(int courseId) { UserCourse uc = new UserCourse(); uc.IdCourse = courseId; uc.IdUser = UserId; uc.DateCreated = DateTime.Now; uc.DateAmended = DateTime.Now; uc.Role = "Pupil"; uc.CourseNotes = string.Empty; uc.ActiveStepIndex = 0; UserCoursesRepository.Add(uc); UserCoursesRepository.Save(); } public void DeleteUserCourse(int courseId) { var uc = (UserCoursesRepository.Query.Where(x => x.IdUser == UserId && x.IdCourse == courseId)).Single(); UserCoursesRepository.Delete(uc); UserCoursesRepository.Save(); } Ajax I am using Ajax via Ajax.BeginForm I don't think that is relevant. ASP.NET MVC 3 I am using mvc3, but don't think that is relevant: the errors are related to model code.

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• initializing properties with private sets in .Net

  - by Martin Neal

  public class Foo { public string Name { get; private set;} // <-- Because set is private, } void Main() { var bar = new Foo {Name = "baz"}; // <-- This doesn't compile /*The property or indexer 'UserQuery.Foo.Name' cannot be used in this context because the set accessor is inaccessible*/ using (DataContext dc = new DataContext(Connection)) { // yet the following line works. **How**? IEnumerable<Foo> qux = dc.ExecuteQuery<Foo>( "SELECT Name FROM Customer"); } foreach (q in qux) Console.WriteLine(q); } I have just been using the private modifier because it works and kept me from being stupid with my code, but now that I need to create a new Foo, I've just removed the private modifier from my property. I'm just really curious, why does the ExecuteQuery into an IEnumerable of Foo's work?

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• Lambda expressions and nullable types

  - by Mathew

  I have two samples of code. One works and returns the correct result, one throws a null reference exception. What's the difference? I know there's some magic happening with capturing variables for the lambda expression but I don't understand what's going on behind the scenes here. int? x = null; bool isXNull = !x.HasValue; // this works var result = from p in data.Program where (isXNull) select p; return result.Tolist(); // this doesn't var result2 = from p in data.Program where (!x.HasValue) select p; return result2.ToList();

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• Eager loading in EF1.0

  - by Dave Swersky

  I have a many-to-many relationship: Application - Applications_Servers - Server This is set up in my Entity Data Model and all is well. My problem is that I'd like to eager-load the whole graph of Applications so that I have an IEnumerable<Applications>, each Application member populated with the Servers collection associated by the many-to-many relationship. Normally this wouldn't be a problem, but according to my research there must be a navigation property between Application and Server. This is not the case for me because my Applications_Servers join table has more in it than just the two keys. Therefore, there is no navigation property directly between Application and Server, and this doesn't work: var apps = (from a in context.Application.Include("Server") select a).ToList(); I get an error saying there is no navigation property on Application called "Server", and that's correct, there is none. How do I write the query to eager-load my Applications with their Servers in this case?

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• ToList()-- Does it Create a New List?

  - by Ngu Soon Hui

  Let's say I have a class public class MyObject { public int SimpleInt{get;set;} } And I have a List<MyObject>, and I ToList() it and then change one of the SimpleInt, will my change be propagated back to the original list. In other words, what would be the output of the following method? public void RunChangeList() { var objs = new List<MyObject>(){new MyObject(){SimpleInt=0}}; var whatInt = ChangeToList(objs ); } public int ChangeToList(List<MyObject> objects) { var objectList = objects.ToList(); objectList[0].SimpleInt=5; return objects[0].SimpleInt; } Why? P/S: I'm sorry if it seems obvious to find out. But I don't have compiler with me now...

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