Entity Framework Not Saving Child Link

Question

I am inserting or updating a parent entity with associated children entities. Entity framework inserts or updates the entities BUT it never creates or updates the links between them even though they exist in C#.

public void MergeParent(Parent parent)
{
    // Set Parent
    var parentInDB = context.Parents.SingleOrDefault(p => p.ParentID == parent.ParentID);

    if (parentInDB != null)
    {
        parent.ID = parentInDB.ID;
        context.Entry(parentInDB).CurrentValues.SetValues(parent);
    }
    else
    {
        context.parents.Add(parent);
    }

    // Set child
    foreach(var child in parent.children)
    {
        var childInDB = context.children.SingleOrDefault(a => a.DiscogsID == child.DiscogsID && child.DiscogsID != null);

        if (childInDB != null)
        {
            child.ID = childInDB.ID;
            context.Entry(childInDB).CurrentValues.SetValues(child);
        }
        else
        {
            context.children.Add(child);
        }
    }

    // Finally Save
    context.SaveChanges();
}

If I set a breakpoint, I can see the parent has the children associated, but while the database contains the elements it does not ever update the link table.

Painful, but this is how it can be done. http://stackoverflow.com/questions/5538974/the-relationship-could-not-be-changed-because-one-or-more-of-the-foreign-key-pro/5540956#5540956 — Steve Greene, May 28 '15 at 19:49

jjj · Accepted Answer · 2015-05-28T21:02:38.240

   // Set child
   foreach(var child in parent.children)
   {
       var childInDB = context.children.SingleOrDefault(a => a.DiscogsID == child.DiscogsID && child.DiscogsID != null);

       if (childInDB != null)
       {
           child.ID = childInDB.ID;
           context.Entry(childInDB).CurrentValues.SetValues(child);
       }
       else
       {
           context.children.Add(child);
       }
   }

The problem is in the section above, for the children, you're adding to and retrieving from the database instead of from the parentInDb's collection of children. I don't think SetValues updates relationships.

I modified some of your code and added some comments:

// Add an include to bring in the children
var parentInDB = context.Parents.Include(p => p.children)
    .SingleOrDefault(p => p.ParentID == parent.ParentID);

if (parentInDB != null)
{
    // This line shouldn't be necessary...
    // parent.ID = parentInDB.ID;
    context.Entry(parentInDB).CurrentValues.SetValues(parent);

    // Set child
    foreach(var child in parent.children)
    {
        // Should search in parentInDB, not context 
        // If DiscogsID is a primary key, it can't be null
        var childInDB = parentInDB.children.SingleOrDefault(a => a.DiscogsID == child.DiscogsID);

        if (childInDB != null)
        {
            // This line shouldn't be necessary...
            // child.ID = childInDB.ID;
            context.Entry(childInDB).CurrentValues.SetValues(child);
        }
        else
        {
            // Should add to parentInDB, not context
            parentInDB.children.Add(child);
        }            
    }
    // Would children in parentInDB.children not found in parent.children need to be removed?
}
else
{
    // This will automatically add untracked children
    context.parents.Add(parent);
}

// Finally Save
context.SaveChanges();

I don't know what happens if you add a new parent with previously attached entities in children.

@Steve Greene's link in his comment shows a more complete example with children that need to be removed — jjj, May 28 '15 at 21:01
There might be a better way of doing it but setting the ID to the InDB ID stops EF from updating an existing record with a null ID. — Three Value Logic, May 30 '15 at 09:40

Entity Framework Not Saving Child Link

1 Answers1