Entity Framework Update Entity along with child entities (add/update as necessary)

Question

I have a many-to-many relationship between Issues and Scopes in my EF Context. In ASP.NET MVC, I bring up an Edit form that allows the user to edit a

Answer 1

Stubs are generally only effective for 1-* relationships. *-* relationships introduce a different set of challenges.

Namely that when you attach both ends - unlike 1-* - you still have no idea if the relationship already exists or not.

So that means that this code:

if (issue.Scopes.Contains(thisScope))

Is probably going to return false every time.

What I would do is this:

edmx.Issues.Attach(issue);
UpdateModel(issue);
// or ctx.LoadProperty(issue, "Scopes") if it is a POCO class.
issue.Scopes.Load(); // hit the database to load the current state.

Now you need to find out what you need to add & remove from issue.Scopes. You can do this by comparing based on ID.

i.e. if you have a set of Scope IDs you want to have related to the issue (relatedScopes)

Then this code works out what to add and what to remove.

int[] toAdd = relatedScopes.Except(issue.Scopes.Select(s => s.ID)).ToArray();
int[] toRemove = issue.Scopes.Select(s => s.ID).Except(relatedScopes).ToArray();

Now for toAdd you do this:

foreach(int id in toAdd)
{
   var scope = new Scope{Id = id};
   edmx.Scopes.Attach(scope);
   issue.Scopes.Add(scope);
}

And for each scope you need to remove

foreach(int id in toRemove)
{
   issue.Scopes.Remove(issue.Scopes.Single(s => s.ID == id));
}

By now the correct relationships should be formed.

Hope this helps

Alex

Microsoft