Attaching Entities when using ObjectContext having lifetime of Http Request - entity-framework

Question

I'm using .NET 3.5 SP1 in ASP.NET MVC application.
While using ObjectContext with Http Request lifetime, and trying to attach an entity ALREADY present in context, we get error:
"An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key."
For Example, the code :
Category newCategory = new Category {CategoryId = CategoryIdSelected};
ctx.AttachTo("CategorySet", newCategory);
will give error if 'Category' with CategoryId = CategoryIdSelected exists in ObjectContext.
Modified code to check for existing entity:
Category newCategory = new Category {CategoryId = CategoryIdSelected};
ObjectStateEntry stateEntry = null;
if( ctx.ObjectStateManager.TryGetObjectStateEntry(newCategory, out stateEntry)){
//EntityObject already attached in context, get it
newCategory = (EntityObject)stateEntry.Entity;
}else{
ctx.AttachTo("CategorySet", newCategory);
}
The modified code is still giving same error:
"[System.InvalidOperationException] = {"An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key."
Please advise ?
Thank You
QUESTION ADDENDUM:
More problems attaching Entities when using ObjectContext having lifetime of Http Request.
For Example, if we have 'AppUser','Category' and Department entities.
public class AppUser : System.Data.Objects.DataClasses.EntityObject{
public int Uid {get; set;}
public string UserName {get; set;}
public string Password {get; set;}
public Department Dept {get; set;}
public Category catg {get; set;}
...........
}
AppUser has relationship with Department and Category Entities.
Now when trying to attach 'user':
user = new AppUser{Uid=1,catg = new Category {categoryId=10}, Dept = new Department{departmentId=101}, ...}
var key = ctx.CreateEntityKey("AppUserSet", user);
if (ctx.ObjectStateManager.TryGetObjectStateEntry(key, out stateEntry)) {
will work ONLY if, in context :
there is NO Category with categoryId=10, and
there is NO Department with departmentId=101
One option, is to ensure context does not have attached entities by always retrieving using NOMERGE NoTracking option. BUT I found following problems with MergeOption.NoTracking:
Second call would still result in db hit
You don't get EntityKeys on EntityRefs. So EntityKey of XXXReference is null,which means NO FK Stub. Please see.
How to get EntityKey of Reference w/o loading both ends (both entities)?
Even though Entity are Detached, they have a reference to the DataContext (via entity._realtionships._context). Please see.
Please advise.
Thank You.

Answer 1

Your code is using two different contexts. You check one, and then attach to the other:
if( csContext. //...){
///
}else{
ctx. // ...
}
The entity appears to be in ctx, but not in csContext. My advice is to use only one context at a time whenever possible; it's much less confusing.
Update
OK, you've changed the code in your question.
My guess is that your stub object doesn't have an EntityKey, so TryGetObjectStateEntry is returning false. Try:
if( ctx.ObjectStateManager.TryGetObjectStateEntry(
new EntityKey("MyEntities.CategorySet", "CategoryId", CategoryIdSelected),
out stateEntry)){
Obviously, replace "MyEntities" with the actual model name.