I&#39;ve read through LOTS of posts on saving a detached entity in Entity Framework. All of them seem to apply to older versions of Entity Framework. They reference methods such as ApplyCurrentValues and ChangeObjectState which do not seem to exist. On a whim I decided to try a method I found through intellisense and I want to make sure this is the correct way to do this since I don&#39;t get to see what happening behind the scenes:

    public void SaveOrder(Order order)
    {
        using (VirtualWebEntities db = new VirtualWebEntities())
        {
            db.Orders.Attach(order);
            db.Entry(order).State = System.Data.Entity.EntityState.Modified;
            db.SaveChanges();
        }
    }

**Is this the correct way to update an existing item that was changed?**

Save detached entity in Entity Framework 6

according to Microsft in this [article][1] is should see an option &#39;Code First From Database&#39;
when adding a new item to the project under &#39;ADO.NET Entity Data Model&#39; in step 3.

I see the following only ![enter image description here][2]

I have installed EF 6.1 using nuget, I am using Visual Studio 2012 Ultimate..What am i missing?




  [1]: http://msdn.microsoft.com/en-us/data/jj200620.aspx
  [2]: http://i.stack.imgur.com/7uQHq.png

&#39;Code First From Database&#39; Template not showing in Visual Studio Entity Data Model Wizard

I&#39;m using EF 6.0 with LINQ in MVC 5 project. I want to log all the SQL queries executed by the Entity Framework DbContext for debugging/performance-measurement purpose.

In Java/Hibernate, equivalent behavior can be achieved by setting the property `hibernate.show_sql=true`. Is it possible to have a similar behavior in Entity Framework?

Log Queries executed by Entity Framework DbContext

I have my core project in C#.

I work on a database, where some tables have the columns &quot;user_mod&quot; and &quot;date_mod&quot; for sign who and when made some mods and the same with &quot;data_new&quot; and &quot;user_new&quot;.

My question: is there a way to centralize this and make this data inserted automatically, where I create the instance of `dbContext`?

If not, I will use an audit trail tool. I have seen some of these, but there is a problem: all of these, require some code in my model. But I don&#39;t want to write in my model, because if I have to change it, I will lost the mods. Is it possible use an audit trail for EF6 without writing in the model file(s)? How?


EDIT:

My attempt to override the saveChanges.


    public partial class PieEntities : DbContext
    {
        public override int SaveChanges(System.Data.Objects.SaveOptions options)
        {
            var timestamp = DateTime.Now;

            EntityState es = EntityState.Added;
            ObjectStateManager o = new ObjectStateManager();
     
            foreach (ObjectStateEntry entry in o.GetObjectStateEntries(EntityState.Added ))  {
                if (entry.Entity.GetType() == typeof(TabImpianti)) {
                    TabImpianti impianto = entry.Entity as TabImpianti;
                    impianto.DATA_INS = timestamp;
                    impianto.DATA_MOD = timestamp;
                    string u = mdlImpostazioni.p.UserName;
                    impianto.USER_INS = u;
                    impianto.USER_MOD = u;
                }
            }
            return base.SaveChanges(options);
        }
    }

**UPDATE: I&#39;ve summarized the [solution here][1].**


  [1]: https://programmingistheway.wordpress.com/2016/02/11/entity-framework-6-audittrack-changes/

Entity Framework 6: audit/track changes

I am trying to update a record using EF6. First finding the record, if it exists, update. 
Here is my code:

    var book = new Model.Book
    {
    	BookNumber =  _book.BookNumber,
    	BookName = _book.BookName,
    	BookTitle = _book.BookTitle,
    };
    using (var db = new MyContextDB())
    {
    	var result = db.Books.SingleOrDefault(b =&gt; b.BookNumber == bookNumber);
    	if (result != null)
    	{
    		try
    		{
    			db.Books.Attach(book);
    			db.Entry(book).State = EntityState.Modified;
    			db.SaveChanges();
    		}
    		catch (Exception ex)
    		{
    			throw;
    		}
    	}
    }


Every time I try to update the record using the above code, I am getting this error:

&gt; {System.Data.Entity.Infrastructure.DbUpdateConcurrencyException: Store
&gt; update, insert, or delete statement affected an unexpected number of
&gt; rows (0). Entities may have been modified or deleted since entities
&gt; were loaded. Refresh ObjectStateManager entries

How to update record using Entity Framework 6?

I&#39;ve got multiple classes (including TPT) in my project. Each POCO has a `BaseClass`, which has a `GUID` (called `GlobalKey`) as primary key.

First I used `DataAnnotations` to create correct foreign keys. But then I&#39;ve got problems synchronizing the corresponding GUID with the object itself.

Now I want to have only one virtual navigation property so that the GUID field in the database is created by `NamingConvention`. But the field name always adds an underscore followed by the word `GlobalKey` (which is right). When I want to remove the underscore, I don&#39;t want to go thru all my POCOs in the fluent API to do this:

    // Remove underscore from Navigation-Field     
    modelBuilder.Entity&lt;Person&gt;()
                .HasOptional(x =&gt; x.Address)
                .WithMany()
                .Map(a =&gt; a.MapKey(&quot;AddressGlobalKey&quot;));

Any ideas to do this for all POCOS by overwriting a convention?

Thanks in advance.

Andreas


How do I remove underscore of foreign key fields in code first by convention


I want to enforce Unique constraint in a table &amp; I am using Entity Framework Code-First.

Is it possible to add a unique constraint using EF 6 as i believe in earlier versions it was not possible.

Is it possible to set a unique constraint using Entity Framework Code First?

I can&#39;t believe I couldn&#39;t find a working solution to this after an hour of searching. I&#39;m following [this article](http://www.dotnetcurry.com/showarticle.aspx?ID=941) on Entity Framework 6.0 which gives a simple walk-through on Code First. I created the project and installed the latest [EF Nuget package](https://www.nuget.org/packages/EntityFramework/6.0.2) for the project to compile. I also verified that I have Microsoft SQL Server 2012 Express LocalDB installed which came with Visual Studio 2013. I don&#39;t have any other instances of SQL installed on my local computer. The program runs and entries are added to the database and outputted in the console. But when the article says &quot;check your localdb&quot; it doesn&#39;t say how! I don&#39;t see any &#39;.mdf&#39; or &#39;.ldf&#39; files created under the project folder. I tried every way to connect Visual Studio&#39;s Server Explorer to LocalDB. The wizard cannot locate `(localdb)` or cannot find any provider in Server Explorer to accept connection string like `(localdb)\v11.0;Integrated Security=true;` I&#39;ve seen this asked several places in StackOverflow but no answer works or marked as answer. Please help, this doesn&#39;t have to be this frustrating!

What are the steps to connect Visual Studio Server Explorer to LocalDB?

How to connect to LocalDB in Visual Studio Server Explorer?

I&#39;m trying to build an EF Entity with Code First, and an `EntityTypeConfiguration` using fluent API. creating primary keys is easy but not so with a Unique Constraint. I was seeing old posts that suggested executing native SQL commands for this, but that seem to defeat the purpose. is this possible with EF6?

Setting unique Constraint with fluent API?

I am just starting out with Unit testings and TDD in general. I have dabbled before but now I am determined to add it to my workflow and write better software.

I asked a question yesterday that kind of included this, but it seems to be a question on its own.  I have sat down to start implementing a service class that I will use to abstract away the business logic from the controllers and map to specific models and data interactions using EF6.

The issue is I have roadblocked myself already because I didn&#39;t want to abstract EF away in a repository (it will still be available outside the services for specific queries, etc) and would like to test my services (EF Context will be used).

Here I guess is the question, is there a point to doing this? If so, how are people doing it in the wild in light of the leaky abstractions caused by IQueryable and the many great posts by [Ladislav Mrnka][1] on the subject of unit testing not being straightforward because of the differences in Linq providers when working with an in memory implementation as apposed to a specific database.

The code I want to test seems pretty simple. (this is just dummy code to try and understand what i am doing, I want to drive the creation using TDD)

**Context**

    public interface IContext
    {
        IDbSet&lt;Product&gt; Products { get; set; }
        IDbSet&lt;Category&gt; Categories { get; set; }
        int SaveChanges();
    }

    public class DataContext : DbContext, IContext
    {
        public IDbSet&lt;Product&gt; Products { get; set; }
        public IDbSet&lt;Category&gt; Categories { get; set; }

        public DataContext(string connectionString)
                    : base(connectionString)
        {

        }
    }


**Service**

    public class ProductService : IProductService
    {
        private IContext _context;

        public ProductService(IContext dbContext)
        {
            _context = dbContext;
        }

        public IEnumerable&lt;Product&gt; GetAll()
        {
            var query = from p in _context.Products
                        select p;
            
            return query;
        }
    }


Currently I am in the mindset of doing a few things:

1. Mocking EF Context with something like this approach- [Mocking EF When Unit Testing][2] or directly using a mocking framework on the interface like moq - taking the pain that the unit tests may pass but not necessarily work end to end and back them up with Integration tests?
2. Maybe using something like [Effort][3] to mock EF - I have never used it and not sure if anyone else is using it in the wild?
3. Not bother testing anything that simply calls back to EF - so essentially service methods that call EF directly (getAll etc) are not unit tested but just integration tested?

Anyone out there actually doing this out there without a Repo and having success?

  [1]: https://stackoverflow.com/users/413501/ladislav-mrnka
  [2]: http://www.asp.net/web-api/overview/testing-and-debugging/mocking-entity-framework-when-unit-testing-aspnet-web-api-2
  [3]: https://entityframework-effort.net/

How are people unit testing with Entity Framework 6, should you bother?

When I am in a detached scenario and get a dto from the client which I map into an entity to save it I do this:

    context.Entry(entity).State = EntityState.Modified;
    context.SaveChanges();

For what is then the `DbSet.Attach(entity)`

or why should I use the .Attach method when EntityState.Modified already attaches the entity?

DbSet.Attach(entity) vs DbContext.Entry(entity).State = EntityState.Modified

Sql server table:

    SomeId PK varchar(50) not null 
    OtherId PK int not null


How should I map this in EF 6 code first?


    public class MyTable
    {
        [Key]
        public string SomeId { get; set; }
    
    	[Key]
        public int OtherId { get; set; }
    }


I&#39;ve seen some examples where you have to set the order for each column, is that required?

Is there official documentation on this somewhere?

Mapping composite keys using EF code first

Update-Database failed from Package Manager Console.
I&#39;ve used Entity Framework 6.x and code-first approach.
Error is

 **&quot;There is already an object named &#39;AboutUs&#39; in the database.&quot;**

How can I solve this problem?

    internal sealed class Configuration 
        : DbMigrationsConfiguration&lt;Jahan.Blog.Web.Mvc.Models.JahanBlogDbContext&gt;
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = true;
            AutomaticMigrationDataLossAllowed = false;
        }

        protected override void Seed(Jahan.Blog.Web.Mvc.Models.JahanBlogDbContext context)
        {
           
        }
    }

My DbContext is:

    public class JahanBlogDbContext : IdentityDbContext&lt;User, Role, int, UserLogin, UserRole, UserClaim&gt;
    {
        public JahanBlogDbContext()
            : base(&quot;name=JahanBlogDbConnectionString&quot;)
        {
            Database.SetInitializer(new DropCreateDatabaseIfModelChanges&lt;JahanBlogDbContext&gt;());
        }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Remove&lt;PluralizingTableNameConvention&gt;();
            modelBuilder.Entity&lt;Comment&gt;().HasRequired(t =&gt; t.Article).WithMany(t =&gt; t.Comments).HasForeignKey(d =&gt; d.ArticleId).WillCascadeOnDelete(true);
            base.OnModelCreating(modelBuilder);

            modelBuilder.Entity&lt;User&gt;().ToTable(&quot;User&quot;);
            modelBuilder.Entity&lt;Role&gt;().ToTable(&quot;Role&quot;);
            modelBuilder.Entity&lt;UserRole&gt;().ToTable(&quot;UserRole&quot;);
            modelBuilder.Entity&lt;UserLogin&gt;().ToTable(&quot;UserLogin&quot;);
            modelBuilder.Entity&lt;UserClaim&gt;().ToTable(&quot;UserClaim&quot;);
        }

        public virtual DbSet&lt;Article&gt; Articles { get; set; }
        public virtual DbSet&lt;ArticleLike&gt; ArticleLikes { get; set; }
        public virtual DbSet&lt;ArticleTag&gt; ArticleTags { get; set; }
        public virtual DbSet&lt;AttachmentFile&gt; AttachmentFiles { get; set; }
        public virtual DbSet&lt;Comment&gt; Comments { get; set; }
        public virtual DbSet&lt;CommentLike&gt; CommentLikes { get; set; }
        public virtual DbSet&lt;CommentReply&gt; CommentReplies { get; set; }
        public virtual DbSet&lt;ContactUs&gt; ContactUs { get; set; }
        public virtual DbSet&lt;Project&gt; Projects { get; set; }
        public virtual DbSet&lt;ProjectState&gt; ProjectStates { get; set; }
        public virtual DbSet&lt;ProjectTag&gt; ProjectTags { get; set; }
        public virtual DbSet&lt;Rating&gt; Ratings { get; set; }
        public virtual DbSet&lt;Tag&gt; Tags { get; set; }
        public virtual DbSet&lt;AboutUs&gt; AboutUs { get; set; }
    }

Package Manage Console:

    PM&gt; update-database -verbose -force
    Using StartUp project &#39;Jahan.Blog.Web.Mvc&#39;.
    Using NuGet project &#39;Jahan.Blog.Web.Mvc&#39;.
    Specify the &#39;-Verbose&#39; flag to view the SQL statements being applied to the target database.
    Target database is: &#39;Jahan-Blog&#39; (DataSource: (local), Provider: System.Data.SqlClient, Origin: Configuration).
    No pending explicit migrations.
    Applying automatic migration: 201410101740197_AutomaticMigration.
    CREATE TABLE [dbo].[AboutUs] (
        [Id] [int] NOT NULL IDENTITY,
        [Description] [nvarchar](max),
        [IsActive] [bit] NOT NULL,
        [CreatedDate] [datetime],
        [ModifiedDate] [datetime],
        CONSTRAINT [PK_dbo.AboutUs] PRIMARY KEY ([Id])
    )
    System.Data.SqlClient.SqlException (0x80131904): There is already an object named &#39;AboutUs&#39; in the database.
       at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
       at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
       at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
       at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean&amp; dataReady)
       at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async, Int32 timeout, Boolean asyncWrite)
       at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite)
       at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
       at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.&lt;NonQuery&gt;b__0(DbCommand t, DbCommandInterceptionContext`1 c)
       at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TTarget,TInterceptionContext,TResult](TTarget target, Func`3 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed)
       at System.Data.Entity.Infrastructure.Interception.DbCommandDispatcher.NonQuery(DbCommand command, DbCommandInterceptionContext interceptionContext)
       at System.Data.Entity.Internal.InterceptableDbCommand.ExecuteNonQuery()
       at System.Data.Entity.Migrations.DbMigrator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement, DbInterceptionContext interceptionContext)
       at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement, DbInterceptionContext interceptionContext)
       at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbTransaction transaction, DbInterceptionContext interceptionContext)
       at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbConnection connection)
       at System.Data.Entity.Migrations.DbMigrator.&lt;&gt;c__DisplayClass30.&lt;ExecuteStatements&gt;b__2e()
       at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.&lt;&gt;c__DisplayClass1.&lt;Execute&gt;b__0()
       at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
       at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Action operation)
       at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements, DbTransaction existingTransaction)
       at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements)
       at System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements(IEnumerable`1 migrationStatements)
       at System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, XDocument targetModel, IEnumerable`1 operations, IEnumerable`1 systemOperations, Boolean downgrading, Boolean auto)
       at System.Data.Entity.Migrations.DbMigrator.AutoMigrate(String migrationId, VersionedModel sourceModel, VersionedModel targetModel, Boolean downgrading)
       at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.AutoMigrate(String migrationId, VersionedModel sourceModel, VersionedModel targetModel, Boolean downgrading)
       at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
       at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
       at System.Data.Entity.Migrations.DbMigrator.UpdateInternal(String targetMigration)
       at System.Data.Entity.Migrations.DbMigrator.&lt;&gt;c__DisplayClassc.&lt;Update&gt;b__b()
       at System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase)
       at System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase)
       at System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration)
       at System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update(String targetMigration)
       at System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.Run()
       at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
       at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
       at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
       at System.Data.Entity.Migrations.Design.ToolingFacade.Update(String targetMigration, Boolean force)
       at System.Data.Entity.Migrations.UpdateDatabaseCommand.&lt;&gt;c__DisplayClass2.&lt;.ctor&gt;b__0()
       at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
    ClientConnectionId:88b66414-8776-45cd-a211-e81b2711c94b
    There is already an object named &#39;AboutUs&#39; in the database.
    PM&gt; 

There is already an object named in the database

Is there a way to create an index on a property/column using code-first, instead of using the new [`IndexAttribute`](https://msdn.microsoft.com/en-us/library/jj591583(v=vs.113).aspx#Anchor_10) ?

How to create index in Entity Framework 6.2 with code first

What is the best approach to update database table data in Entity Framework Core?

 1. Retrieve the table row, do the changes and save
 2. Use keyword **Update** in DB context and handle exception for item not exist

What are the improved features we can use over EF6? 

How to update record using Entity Framework Core?

What is the difference between `System.Transactions.TransactionScope` and EF6&#39;s `Database.BeginTransaction`?

Could someone give a small example or just explain which one to use when with a clear difference?

P.S: In my project, I&#39;m using EF6. I&#39;ve already read the documentation but it didn&#39;t help much. Also looked up the examples but they are rather using `SqlConnection.BeginTransaction` and now MS has introduced this new `Database.BeginTransaction` in EF6.

Database.BeginTransaction vs Transactions.TransactionScope

Under what situation could eager loading be more beneficial than lazy loading?

Lazy loading in Entity Framework is the default phenomenon that happens for loading and accessing the related entities. However, eager loading is referred to the practice of force-loading all these relations.

I&#39;m asking this, because it is obvious that lazy loading is more resource-friendly, and even if we use the `ToList()` method, we can still take advantage of the lazy loading behavior.

However, I thought maybe lazy loading increases the number of requests to the actual database and maybe that&#39;s why sometimes developers use the `Inlcude` method to force-loading all relations.

For example, when using the Visual Studio auto-scaffolding in MVC 5, the Index method automatically created in the controller always uses Eager Loading, and I&#39;ve always had the question of why Microsoft uses Eager Loading default in that case. 

I would appreciate it if someone explains to me under what situation eager loading would be more beneficial than lazy loading, and why do we use it at all while there&#39;s something more resource-friendly as Lazy Loading?

Lazy Loading vs Eager Loading

I am trying to run my tests on TeamCity which is currently installed on my machine.

&gt; `System.InvalidOperationException`: 
&gt; 
&gt; The Entity Framework provider type
&gt; &#39;`System.Data.Entity.SqlServer.SqlProviderServices,
&gt; EntityFramework.SqlServer`, `Version=6.0.0.0, Culture=neutral,
&gt; PublicKeyToken=b77a5c561934e089&#39;` for the &#39;`System.Data.SqlClient`&#39;
&gt; ADO.NET provider could not be loaded. Make sure the provider assembly
&gt; is available to the running application. 
&gt; 
&gt; See http://go.microsoft.com/fwlink/?LinkId=260882 for more
&gt; information..

I have no reference to `System.Data.Entity` in any of my projects as was suggested on codeplex for upgrading to EF6.

So, I am not sure why am I getting this exception.
I do not get any such exception when I run the tests from VS.

I did try to set CopyLocal to false then again to true.. but that does not seem to work either.

Update 

My app.config has the following . Does this cause some behavior that I don&#39;t understand ?

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;configuration&gt;
      &lt;configSections&gt;
        &lt;section name=&quot;entityFramework&quot; type=&quot;System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089&quot; requirePermission=&quot;false&quot; /&gt;
        &lt;!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 --&gt;
      &lt;/configSections&gt;
      &lt;entityFramework&gt;
        &lt;defaultConnectionFactory type=&quot;System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework&quot; /&gt;
      &lt;/entityFramework&gt;
    &lt;/configuration&gt;


I get the following stacktrace in teamcity .


    [MSTest] IntegrationTests.CrudTest+QuestionTest.Create
    [03:59:11][IntegrationTests.CrudTest+QuestionTest.Create] Initialization method IntegrationTests.CrudTest+QuestionTest.Initialize threw exception. System.InvalidOperationException: System.InvalidOperationException: The Entity Framework provider type &#39;System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089&#39; for the &#39;System.Data.SqlClient&#39; ADO.NET provider could not be loaded. Make sure the provider assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information..
    [03:59:11]
    [IntegrationTests.CrudTest+QuestionTest.Create]     at System.Data.Entity.Config.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName)
       at System.Data.Entity.Config.ProviderServicesFactory.GetInstanceByConvention(String providerInvariantName)
       at System.Data.Entity.Config.DefaultProviderServicesResolver.GetService(Type type, Object key)
       at System.Data.Entity.Config.CachingDependencyResolver.&lt;&gt;c__DisplayClass1.&lt;GetService&gt;b__0(Tuple`2 k)
       at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
       at System.Data.Entity.Config.CachingDependencyResolver.GetService(Type type, Object key)
       at System.Data.Entity.Config.ResolverChain.&lt;&gt;c__DisplayClass3.&lt;GetService&gt;b__0(IDbDependencyResolver r)
       at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
       at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
       at System.Data.Entity.Config.ResolverChain.GetService(Type type, Object key)
       at System.Data.Entity.Config.RootDependencyResolver.GetService(Type type, Object key)
       at System.Data.Entity.Config.ResolverChain.&lt;&gt;c__DisplayClass3.&lt;GetService&gt;b__0(IDbDependencyResolver r)
       at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
       at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
       at System.Data.Entity.Config.ResolverChain.GetService(Type type, Object key)
       at System.Data.Entity.Config.CompositeResolver`2.GetService(Type type, Object key)
       at System.Data.Entity.Config.IDbDependencyResolverExtensions.GetService[T](IDbDependencyResolver resolver, Object key)
       at System.Data.Entity.Config.InternalConfiguration.GetService[TService](Object key)
       at System.Data.Entity.Config.DbConfiguration.GetService[TService](Object key)
       at System.Data.Entity.Utilities.DbProviderFactoryExtensions.GetProviderServices(DbProviderFactory factory)
       at System.Data.Entity.Infrastructure.DefaultManifestTokenService.GetProviderManifestToken(DbConnection connection)
       at System.Data.Entity.Utilities.DbConnectionExtensions.GetProviderInfo(DbConnection connection, DbProviderManifest&amp; providerManifest)
       at System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection)
       at System.Data.Entity.Internal.LazyInternalContext.CreateModel(LazyInternalContext internalContext)
       at System.Data.Entity.Internal.RetryLazy`2.GetValue(TInput input)
       at System.Data.Entity.Internal.LazyInternalContext.InitializeContext()
       at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType)
       at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize()
       at System.Data.Entity.Internal.Linq.InternalSet`1.get_InternalContext()
       at System.Data.Entity.Internal.Linq.InternalSet`1.ActOnSet(Action action, EntityState newState, Object entity, String methodName)
       at System.Data.Entity.Internal.Linq.InternalSet`1.Add(Object entity)
       at System.Data.Entity.DbSet`1.Add(TEntity entity)
       at EFRepository.Infrastructure.EFRepository`1.Add(T item) in c:\TeamCity\buildAgent\work\da2ea4e72c0e77f0\Repository\Infrastructure\EFRepository.cs:line 22
       at IntegrationTests.CrudTest.Initialize() in c:\TeamCity\buildAgent\work\da2ea4e72c0e77f0\IntegrationTests\CrudTest.cs:line 34

Entity Framework Provider type could not be loaded?

This is my code:

    var banner = context.Banners.ToListAsync()
    var newsGroup = context.NewsGroups.ToListAsync()
    await Task.WhenAll(banner, newsGroup);

But when i called the function from controller. It showed error

&gt;A second operation started on this context before a previous asynchronous operation completed. Use &#39;await&#39; to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe.


Please help me solve this issue.



Multi-async in Entity Framework 6?

With EF6 you have a new transaction which can be used like:

    using (var context = new PostEntityContainer())
            {
                using (var dbcxtransaction = context.Database.BeginTransaction())
                {
                    try
                    {
                        PostInformation NewPost = new PostInformation()
                        {
                            PostId = 101,
                            Content = &quot;This is my first Post related to Entity Model&quot;,
                            Title = &quot;Transaction in EF 6 beta&quot;
                        };
                        context.Post_Details.Add(NewPost);
                        context.SaveChanges();
                        PostAdditionalInformation PostInformation = new PostAdditionalInformation()
                        {
                            PostId = (101),
                            PostName = &quot;Working With Transaction in Entity Model 6 Beta Version&quot;
                        };

                        context.PostAddtional_Details.Add(PostInformation);
                        context.SaveChanges();

                        dbcxtransaction.Commit();
                    }
                    catch
                    {
                        dbcxtransaction.Rollback();
                    }
                }
            }

Is rollback actually needed when things go sideways? I&#39;m curious because the Commit description says: &quot;Commits the underlying store transaction.&quot;

Whereas the Rollback description says: &quot;Rolls back the underlying store transaction.&quot;

This makes me curious, because it looks to me that if Commit isn&#39;t called, the previously executed commands will not be stored (which seems logical to me). But if that is the case, what would the reason be to call the Rollback function? In EF5 I used TransactionScope which didn&#39;t have a Rollback function (only a Complete) which seemed logical to me. Due to MS DTC reasons I cannot use the TransactionScope anymore, but I also cannot use a try catch like the example above (i.e., I only need the Commit).



Entity Framework 6 transaction rollback

I have a partial view that tries to retrieve a `IEnumerable&lt;Post&gt;` from the database using async...

Method

    public static class PostService
    {
        public static int PostsPerPage = 50;

        public static async Task&lt;IEnumerable&lt;Post&gt;&gt; GetRecentAsync(int page = 0)
        {
            return await entityFrameworkDbContext.Posts
                .ToListAsync();
        }
    }

PartialView

    public async Task&lt;ActionResult&gt; Recent(int page = 0)
    {
        return PartialView(await PostService.GetRecentAsync(page));
    }

And then if I try to call it

    @Html.Action(&quot;Recent&quot;, &quot;Post&quot;)

I get the following exception

&gt; HttpServerUtility.Execute blocked while waiting for an asynchronous operation to complete.
&gt;
&gt; Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
&gt;
&gt; Exception Details: System.InvalidOperationException: HttpServerUtility.Execute blocked while waiting for an asynchronous operation to complete.

Why do I get this error? Shouldn&#39;t it work?

Async PartialView causes &quot;HttpServerUtility.Execute blocked...&quot; exception

Is there a way to find out whether there are unsaved changes in my entity context, in the Entity Framework?

Check if there are any pending changes to be saved

I have an entity with primary key &quot;Id&quot; which is Guid:

    public class FileStore
    {
        public Guid Id { get; set; }
        public string Name { get; set; }
        public string Path { get; set; }
    }

And some configuration:

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity&lt;FileStore&gt;().Property(x =&gt; x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        base.OnModelCreating(modelBuilder);
    }

When I try to insert a record I get a following error:

&gt; Cannot insert the value NULL into column &#39;Id&#39;, table &#39;FileStore&#39;; column does not allow nulls. INSERT fails.\r\nThe statement has been terminated.

I don&#39;t want to generate Guid manually. I just want to insert a record and get `Id` generated by SQL Server. If I set `.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)`, `Id` column is not Identity column in SQL Server.

How can I configure Entity Framework to autogenerate Guid in SQL Server?

Entity Framework 6 GUID as primary key: Cannot insert the value NULL into column &#39;Id&#39;, table &#39;FileStore&#39;; column does not allow nulls

I&#39;ve followed [MSDN](https://msdn.microsoft.com/en-us/data/hh859576.aspx) on how to handle enumerations in Code First for EF6. It worked, as supposed to **but** the field in the created table that refers to the enumerator is a simple *int*.

I&#39;d prefer a second table to be produced, the values of which would follow the definition of the enumerator in C# code. So, instead of only getting a table corresponding to *Department* in the example on MSDN, I&#39;d also like to see a second table populated by the items from *Faculty*.

    public enum Faculty { Eng, Math, Eco }     
     
    public partial class Department 
    { 
      [Key] public Guid ID { get; set; } 
      [Required] public Faculty Name { get; set; } 
    }

Researching the issue, I stumbled upon a [solution](http://gentlelogic.blogspot.se/2014/07/ef-code-first-create-table-out-of-enum.html), which suggests creating a table for the enumeration and populating it explicitly by seeding. 

It appear to me as a cumbersome approach and a lot of work that should be handled automagically. After all, the system knows what actual values that constitute the enumeration. From DB point of view it&#39;s still data rows, just as the entities that I create but from OO aspect, it&#39;s not really a data - rather a type (loosely expressed) that can assume a finite and onbeforehand known number of states.

Is the approach of populating the table &quot;manually&quot; recommended?


How to create a table corresponding to enum in EF6 Code First?

One of my tables have a unique key and when I try to insert a duplicate record it throws an exception as expected. But I need to distinguish unique key exceptions from others, so that I can customize the error message for unique key constraint violations.

All the solutions I&#39;ve found online suggests to cast `ex.InnerException` to `System.Data.SqlClient.SqlException` and check the if `Number` property is equal to 2601 or 2627 as follows:

	try
	{
		_context.SaveChanges();
	}
	catch (Exception ex)
	{
		var sqlException = ex.InnerException as System.Data.SqlClient.SqlException;

		if (sqlException.Number == 2601 || sqlException.Number == 2627)
		{
			ErrorMessage = &quot;Cannot insert duplicate values.&quot;;
		}
		else
		{
			ErrorMessage = &quot;Error while saving data.&quot;;
		}
	}

But the problem is, casting `ex.InnerException` to `System.Data.SqlClient.SqlException` causes invalid cast error since `ex.InnerException` is actually type of `System.Data.Entity.Core.UpdateException`, not `System.Data.SqlClient.SqlException`.

What is the problem with the code above? How can I catch Unique Key Constraint violations?

How can I catch UniqueKey Violation exceptions with EF6 and SQL Server?

In my MVVM program I have a Model class (say `MyModel`) from which I have an instance of reading from the database (using Entity Framework). When retrieving the object I&#39;m presenting all the data to the user. Later on the user will be modifying some fields.  
What I want is to create the same object except for it&#39;s `ID` (since that `ID` is the *primary key* and *auto incremented*).  
So how could I approach this? I don&#39;t want to copy all fields one by one, this is not a robust approach. Because perhaps in the future the model may be modified, so this way I will have to take that into account in the cloning method.  

So is there any elegant way to copy the object and when saving in the database, it&#39;s ID gets auto incremented again? (Setting the ID to `null` gives me a compiler error, because it&#39;s of type `int`).

Entity Framework 6: Clone object except ID

I am using EF6 for storing instances of the `report` class in my database. The database already contains data. Say I wanted to add a property to `report`, 

    public class report {
        // ... some previous properties
    
        // ... new property:
        public string newProperty{ get; set; }
    }

Now if I go to the package-manager console and execute 
    
    add-migration Report-added-newProperty
    update-database

I will get a file in the &#39;/Migrations&#39; folder adding a `newProperty` column to the table. This works fine. However, on the older entries in the database, the value for the `newProperty` is now an empty string. But I want it to be, e.g., &quot;old&quot;. 

So my question is: How do I set default values for new properties (of any type) in the migration script (or elsewhere)?

Code-first migration: How to set default value for new property?

The code I have got so far works fine

```
public async Task&lt;ActionResult&gt; Details(Guid? id)
{
	if (id == null)
	{
		return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
	}

	ItemDetailModel model = new ItemDetailModel();
	model.Item = await db.Items.FindAsync(id);
	if (model.Item == null)
	{
		return HttpNotFound();
	}

	return View(model);
}
```


But I want to include 1 table more and cannot use `FindAsync`

```
public async Task&lt;ActionResult&gt; Details(Guid? id)
{
	if (id == null)
	{
		return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
	}

	ItemDetailModel model = new ItemDetailModel();
	model.Item = await db.Items.Include(i=&gt;i.ItemVerifications).FindAsync(id);

	if (model.Item == null)
	{
		return HttpNotFound();
	}           

	return View(model);
}
```

So I am facing this error

&gt; Severity	Code	Description	Project	File	Line	Suppression State
&gt; Error	CS1061	&#39;IQueryable&lt;Item&gt;&#39; does not contain a definition for
&gt; &#39;FindAsync&#39; and no extension method &#39;FindAsync&#39; accepting a first
&gt; argument of type &#39;IQueryable&lt;Item&gt;&#39; could be found (are you missing a
&gt; using directive or an assembly reference?)

Any clue how to fix it?

FindAsync and Include LINQ statements

Assumptions
-------

 - Using EF 6.1, MVC 5, VS 2013, C#

 - I have an existing database model designed in Toad DM for SQL Server and it&#39;s very important keep it always updated

Steps and Notes
-----

 1. Using ADO.NET Entity Data Model I chose **Code First from Database** (**new feature in EF 6.1**) to generate the models. Note: Model classes and DbContext class generated successfuly but **NO .edmx or .tt file was generated**.

 2. Next I added a new scaffold item: MVC 5 Controllers with views, using Entity Framework. Note: Success, controllers and views generated

Question
--------

From now on I don&#39;t want to use Code First to update my database. Instead I want the models to be updated based on database changes. What to do next? If I don&#39;t have an edmx file will I not be able to update my model classes from the database?

How to sync model after using Code First from Database using Entity Framework 6.1 and MVC 5?

What happens when we start multiple async Entity Framework queries and **run them in parallel?**

Are they physically executed in parallel? Are they serialized by Entity Framework? Is this unsupported? Does it result in an exception?

    public async Task QueryDatabase()
    {
        using (var context = new MyDbContext())
        {
            Task task1 = context.SomeTable1.ToListAsync();
            Task task2 = context.SomeTable2.ToListAsync();
    
            await Task.WhenAll(task1, task2);
        }
    }


Does Entity Framework support parallel async queries?

I have the following 2 classes:

    public class Reward 
    {
        public int Id { get; set; }
        public int CampaignId { get; set;
        public virtual Campaign Campaign { get; set; }
    }

    public class Campaign 
    {
        public int Id { get; set; }
        public virtual ICollection&lt;Reward&gt; Rewards { get; set; }
    }

With this I have all the obvious necessary stuff like a DbContext and mappings. 

Now let&#39;s say I create a Reward entity and insert it like this:
    
    var reward = new Reward { CampaignId = 1 };
    context.Set&lt;Reward&gt;().Add(reward);
    context.SaveChanges();

    reward = context.Set&lt;Reward&gt;().SingleOrDefault(a =&gt; a.Id == reward.Id);
    //reward.Campaign is null

I obviously have a campaign with Id 1 so the FK constraint is happy. After this insert, my reward entity has it&#39;s new Identity Id set. Now the problem is that reward is still just the Reward entity I created. And with this, the reward.Campaign property is null. It seems like EF is keeping the inserted entities in memory, and when I then do a .SingleOrDefault(a =&gt; a.Id == reward.Id) it simply returns the entity in memory, and not a new proxy. This is probably a good thing.

So the question is: How does one access or load the navigation properties after an insert or get a new proxy that has the navigation properties as proxies as well.

Am I perhaps inserting in the wrong way?

    


Get entity navigation properties after insert

I see already a un-answered question [here on][1].

My question is -

&gt; Is EF really production ready for large application?

The question originated from these underlying questions -

 1. EF pulls all the records into memory then performs the query
    operation. How EF would behave when table has around ~1000 records?
 2. For simple edit I have to pull the record edit it and
        then push to db using `SaveChanges()`




  [1]: https://stackoverflow.com/questions/14205033/entity-dealing-with-large-number-of-records-35-mlns

All Entity Framework-6 Solutions on Gang of Coders

Total of 32 Entity Framework-6 Solutions