One DbContext per web request… why?

Question

I have been reading a lot of articles explaining how to set up Entity Framework\'s DbContext so that only one is created and used per HTTP web request using var

Answer 1

Another issue to watch out for with Entity Framework specifically is when using a combination of creating new entities, lazy loading, and then using those new entities (from the same context). If you don't use IDbSet.Create (vs just new), Lazy loading on that entity doesn't work when its retrieved out of the context it was created in. Example:

 public class Foo {
     public string Id {get; set; }
     public string BarId {get; set; }
     // lazy loaded relationship to bar
     public virtual Bar Bar { get; set;}
 }
 var foo = new Foo {
     Id = "foo id"
     BarId = "some existing bar id"
 };
 dbContext.Set().Add(foo);
 dbContext.SaveChanges();

 // some other code, using the same context
 var foo = dbContext.Set().Find("foo id");
 var barProp = foo.Bar.SomeBarProp; // fails with null reference even though we have BarId set.