entity-framework - w3toppers.com

Solving “The ObjectContext instance has been disposed and can no longer be used for operations that require a connection” InvalidOperationException

By default Entity Framework uses lazy-loading for navigation properties. That’s why these properties should be marked as virtual – EF creates proxy class for your entity and overrides navigation properties to allow lazy-loading. E.g. if you have this entity: public class MemberLoan { public string LoandProviderCode { get; set; } public virtual Membership Membership { … Read more

EF codefirst : Should I initialize navigation properties?

Collections: It doesn’t matter. There is a distinct difference between collections and references as navigation properties. A reference is an entity. A collections contains entities. This means that initializing a collection is meaningless in terms of business logic: it does not define an association between entities. Setting a reference does. So it’s purely a matter … Read more

EntityFramework – contains query of composite key

This is a nasty problem for which I don’t know any elegant solution. Suppose you have these key combinations, and you only want to select the marked ones (*). Id1 Id2 — — 1 2 * 1 3 1 6 2 2 * 2 3 * … (many more) How to do this is a … Read more

How to call Stored Procedure in Entity Framework 6 (Code-First)?

You can call a stored procedure in your DbContext class as follows. this.Database.SqlQuery<YourEntityType>(“storedProcedureName”,params); But if your stored procedure returns multiple result sets as your sample code, then you can see this helpful article on MSDN Stored Procedures with Multiple Result Sets

Entity Framework Code First – two Foreign Keys from same table

Try this: public class Team { public int TeamId { get; set;} public string Name { get; set; } public virtual ICollection<Match> HomeMatches { get; set; } public virtual ICollection<Match> AwayMatches { get; set; } } public class Match { public int MatchId { get; set; } public int HomeTeamId { get; set; } public … Read more

Validation failed for one or more entities. See ‘EntityValidationErrors’ property for more details [duplicate]

To be honest I don’t know how to check the content of the validation errors. Visual Studio shows me that it’s an array with 8 objects, so 8 validation errors. Actually you should see the errors if you drill into that array in Visual studio during debug. But you can also catch the exception and … Read more

LINQ to Entities does not recognize the method

As you’ve figured out, Entity Framework can’t actually run your C# code as part of its query. It has to be able to convert the query to an actual SQL statement. In order for that to work, you will have to restructure your query expression into an expression that Entity Framework can handle. public System.Linq.Expressions.Expression<Func<Charity, … Read more

There is already an open DataReader associated with this Command which must be closed first

This can happen if you execute a query while iterating over the results from another query. It is not clear from your example where this happens because the example is not complete. One thing that can cause this is lazy loading triggered when iterating over the results of some query. This can be easily solved … Read more

Code-first vs Model/Database-first [closed]

I think the differences are: Code first Very popular because hardcore programmers don’t like any kind of designers and defining mapping in EDMX xml is too complex. Full control over the code (no autogenerated code which is hard to modify). General expectation is that you do not bother with DB. DB is just a storage … Read more

Code First: Independent associations vs. Foreign key associations?

If you want to take full advantage of ORM you will definitely use Entity reference: public class Order { public int ID { get; set; } public Customer Customer { get; set; } // <– Customer object … } Once you generate an entity model from a database with FKs it will always generate entity … Read more