Question

I have a many to many relationship in my EF4 model (many groups can have many programs).

I have a set of program Id’s and a group. I want my group to have the programs that are represented by the program Id’s that I have.

What I don’t want to do is go to the database to get the program entities. I already know their Id’s.

How do I do this?

Answer 1

Use a trick with dummy classes:

// you have a group
var group = GetGroupSomehow();
// if group is unknown to the context Attach it
context.Groups.Attach(group); // if it is a new group use AddObject
// now add programs
foreach(var program in programId.Select(id => new Program { Id = id }))
{
    // Attach dummy program first
    context.Programs.Attach(program);
    // Now make relation between group and program
    group.Programs.Add(program);
} 

context.SaveChanges();

The only requirement is that none Program from programIds is already loaded. If any program is loaded it will be more complicated because you will first have to check it in ObjectStateManager and use loaded instance.