Entity Framework Not Saving Child Link - entity-framework

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.

Answer 1

// 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.