Problem with Adding multiple child objects to an existing entity in EF

Question

I need to add multiple child objects to an existing parent Object. I am instantiating my parent object and sets it Key/Id in my UI processing layer(to which my child objects will be added).

    Parent parenttoModify = new Parent();
    parenttoModify.Parent_Id = 5; //this comes from some Index of a dropdown or a key column of a grid, i Have put a dummy value here for example
    parenttoModify.Children.Add(child);
    parenttoModify.Children.Add(child2);
    DataAccess.ModifyParent(parenttoModify);

In my data access layer I have a method like :

public static bool ModifyParent(Parent parent)
        {
            int recordsAffected=0;
            using (TestEntities testContext = new TestEntities())
            {

                testContext.Parents.Attach(parent);
                var parentEntry = testContext.ObjectStateManager.GetObjectStateEntry(parent);
                parentEntry.ChangeState(System.Data.EntityState.Modified);
                recordsAffected =  testContext.SaveChanges();
            }
            return recordsAffected > 0 ? true : false;

        }

I get an error when testContext.Parent.Attach(parent) is called. It says:

Object with same key already exist.

I am not sure why is this happening since i am not adding a parent object, I am just attaching it and adding child objects within it.

Any idea where I am going wrong?

Ladislav Mrnka · Accepted Answer · 2011-06-07 06:57:32Z

2

Where do you add childs? I guess you are not showing all code. When you call Attach or AddObject EF always attaches or adds all entities from object graph which are not known (tracked) to context at the moment. The exception says that some entity - probably parent - is already tracked by the context. So you have either:

Used shared context (you are creating a new instance in ModifyParent so it should not be a case)
Load parent from the context first in ModifyParent
Called Attach or AddObject on any child before attaching parent.

All these operations lead to the exception you are receiving.

answered Jun 7, 2011 at 6:57

Ladislav Mrnka

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5 Comments

Kunal Over a year ago

I am creating instances of my child objects in my UI processing layer , so in this case child and Child2 are created before adding them to the parent objects

Kunal Over a year ago

Exception occurs when I add multiple child(thats the problem I highlighted in my question as well). If I just add one child object, program successfully executes. I have one to many relationship between Parent table and a child table in the database

Slauma Over a year ago

@Kunal: You must add child and child2 to parenttoModify.Children after you have attached the parent to the context. Otherwise the whole object graph - parent plus children - will be attached to the context as Ladislav explained. It means that child and child2 will not be in Added state but in state Unchanged, so EF considers them as existing objects with a valid entity key. Because you have created the child objects from scratch their key will be probably 0 (or whatever your default is). So, EF assumes there are two existing child entities with the same key 0->exception!

Kunal Over a year ago

@Slauma: + One for your explanation but thats bad from the design point of view, it implies that I need to send a seperate list of child objects from my UI processing layer. Is there a way to send only parents objects and child attached within them rather than sending a seperate list of child objects

Slauma Over a year ago

@Kunal: You could try to loop through the Children collection and add each child object to the context before you attach the parent. Note, that the child objects must not have a reference set to the parent, otherwise EF would add the parent to the context too. You would probably get a new parent for every single child in the database. Not sure if this would work though.

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