Add item and update relationship in transitional table in many-to-many database Sql Server

Question

--here was wrong model without association manyTOmany between A-B. corrected is in EDIT2--

A exists in database, B exists in database. I need only enter new C element with some Properties1 and Properties2 (and update collections of C in existed A and B elements)

I tried many options, like for example this, but still somethings wrong (with ObjectOCntext and existed Key etc)

void SaveNewC(C newC)
{
    using (var context = new MyEntities(connectionString))
    {
        var dbA = context.A.Where(a => a.Id == newC.A.Id).SingleOrDefault();
        var dbB = context.B.Where(b => b.Id == newC.B.Id).SingleOrDefault();

        newC.A = dbA;
        newC.B = dbB;
        context.AddObject(newC);

        context.SaveChanges();
    }
}

EDIT

Exception that I get: "An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key."

EDIT2 updated model

enter image description here

Don't have `A` and `B` navigation collections refering to each other? You cannot have a many-to-many relationship without navigation properties. It's also important to know if and how those collections are populated in `newC.A` and `newC.B`. — Slauma, Sep 11 '12 at 09:09
@Slauma You're right. Last time I improve model incorrect without navigtion properties. Now model is fully cmplete — Saint, Sep 11 '12 at 09:14
Try to clear all references in `newC.A` and `newC.B`: `newC.A.C = null; newC.A.B.Clear();` and `newC.B.C = null; newC.B.A.Clear();` and check if it works then. — Slauma, Sep 11 '12 at 10:37
@Slauma Yes, I tried it before, but still the same exception — Saint, Sep 11 '12 at 11:16
There must be something more which is not visible in your example code. If all those references are cleared this exception is impossible. — Slauma, Sep 11 '12 at 13:15
Your model seems really confusing. You have a Many to Many on A -> B which is being mapped, I assume with C. Why do you need to have the C entity at all? EF will automatically hide the junction table away and manage that. If you're planning on having custom logic on C then you should no longer have the Many to Many directly from A->B, but it should go A -> C -> B instead. Otherwise you've created another hidden away junction table (D maybe?) Is this what you intended to do? — Mark Oreta, Sep 11 '12 at 13:21
@Slauma I flag this topic to moderator to remove. See more actual version: http://stackoverflow.com/questions/12372975/many-to-many-with-junction-table-in-entity-framework — Saint, Sep 11 '12 at 15:26
What are you doing :( That's the same question as this one and still this mysterious exception... — Slauma, Sep 11 '12 at 15:58

podiluska · Answer 1 · 2012-09-10T14:51:51.583

0

context.Entry(dbA).State = EntityState.Unchanged;
context.Entry(dbB).State = EntityState.Unchanged;
context.AddObject(newC);
context.SaveChanges();

edited Sep 10 '12 at 14:51

answered Sep 10 '12 at 14:45

podiluska

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There's no "State" property in EntityObject – Saint Sep 10 '12 at 14:47
If you mean `context.ObjectStateManager.ChangeObjectState(dbA, System.Data.EntityState.Unchanged);` I tried it, but I get InvalidOperationException: "`An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.`" - but C object is new one – Saint Sep 10 '12 at 15:00

score 0 · Answer 2 · answered Sep 10 '12 at 15:41

0

Apparently your newC has already populated navigation properties A and B with the correct Ids. Then you can just attach the entities refered by the navigation properties to the context:

void SaveNewC(C newC)
{
    using (var context = new MyEntities(connectionString))
    {
        context.A.Attach(newC.A);
        context.B.Attach(newC.B);

        context.C.AddObject(newC);

        context.SaveChanges();
    }
}

answered Sep 10 '12 at 15:41

Slauma

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While `context.A.Attach(newC.A);` I get exception: `"An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key."` – Saint Sep 11 '12 at 08:03
1

@Saint: Is the code in your question really complete? The first line above happens in a new context, so this context is empty and nothing can't be attached to it before this line. The only reason I could imagine is that `newC.A` has references to other objects and some of these objects in the graph are of the same type and have the same key but are different objects. Does `newC.A` have references to other entities? – Slauma Sep 11 '12 at 08:40
Yes, A and B are in relationship many-to-many. I forgot to add this association at first time. See my EDIT2 – Saint Sep 11 '12 at 08:49

score 0 · Answer 3 · answered Sep 11 '12 at 13:28

0

Do you need to have the junction table mapped? If all your wanting is a Many to Many from A->B you could do it in a simpler way.

If you created the C table as a true junction - and have a FK to A and B set to it's PK in sql like this:

enter image description here

Then when you create your edmx from the model it will create this:

enter image description here

Now, in your code if you wanted to add a relationship, you would simply add it to your collection, and EF will automatically create the relationship in your C table for you:

        var A = new A();
        var b = new B();
        var b2 = new B();

        A.B.Add(b);
        A.B.Add(b2);

answered Sep 11 '12 at 13:28

Mark Oreta

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No, I need this junction table – Saint Sep 11 '12 at 15:20
See more actual version of this topic, this one will be removed: http://stackoverflow.com/questions/12372975/many-to-many-with-junction-table-in-entity-framework – Saint Sep 11 '12 at 15:28

Add item and update relationship in transitional table in many-to-many database Sql Server

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