Question

This question is a continuation of:

EntityFramework adding new object to a collection

Now I understand that when using DbSet EF won’t load the entire collection into memory

But what if I have something like the following code:

public class User
{
    public int UserID { get; set; }
    public string UserName { get; set; }
    public ICollection<Role> Roles { get; set; }
}

public class Role
{
    public int RoleID { get; set; }
    public string RoleName { get; set; }
    public User User { get; set; }
}

public class MyContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Role> Roles { get; set; }
}

public class SomeClass
{
    public void AssignRoleToUser(int userID, Role role)
    {
        var ctx = new MyContext();
        var user = ctx.Users.First(x => x.UserID.Equals(userID));

        user.Roles.Add(role);

        ctx.SaveChanges();
    }
}

In this case, I’m not using the DbSet object to add a new object to the Role collection, instead, I’m adding a new role to a specific user using an ICollection collection

So what happens in this case?

Does EntityFramewrk have to load into memory all the user’s roles in order to perform the insert?

Answer 1

In provide code above you are not adding new role as your ctx.Users is just used to retrieve data. Somewhat similar issue is addressed in this SE post – Linq To Entities – how to filter on child entities.

I would advice to look at this short and useful article – Entity Framework 4.0 FAQ – Getting Started Guide.