mvc4 get results in controller from joining tables (entity framework) - asp.net-mvc

Question

I am not sure how to get the results from joining the tables in controllers.
There're 3 tables 'Groups' 'Users' 'GroupUser' (bridge table).
public class Group
{
[Key]
public int GroupID { get; set; }
public string Group_Name { get; set; }
public ICollection<User> Users { get; set; }
}
public class User
{
[Key]
public int UserID { get; set; }
public string User_Name { get; set; }
public ICollection<Group> Groups { get; set; }
}
I also have this EFContext class
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Group>()
.HasMany(g => g.Users)
.WithMany(u => u.Groups)
.Map(m =>
{
m.MapLeftKey("UserID");
m.MapRightKey("GroupID");
m.ToTable("GroupUSer");
});
Do I also need to build a GroupUser class (to represent the GroupUser bridge table)?
Then how do I get the results when joining the 3 tables to get list of groups and users?
GroupViewModel model = new GroupViewModel
{
Groups = .... // this should be a linq statement that get results
that contains all groups and users
};
The equal sql statemen would be
select *
from Group g
join GroupUser gu on g.GroupID=gu.GroupID
join User u on u.UserID=gu.UserID

Answer 1

No, intermediate class is not needed.
The main point of an ORM (Object-Relational Mapper, which is what Entity Framework is) is to abstract away the database and let you work in a pure object-oriented way. Intermediate tables are definitely a database term and are not needed here.
The only reason I can think of that may lead you to create an intermediate class is when you need a "payload" (an extra meta-data) on the association. For example:
public class User
{
public int Id { get; set; }
public int Email { get; set; }
public virtual ICollection<Account> Accounts { get; set; }
}
public class Account
{
public int Id { get; set; }
public virtual ICollection<User> Users { get; set; }
}
Now, if you want the user-to-account association to define whether the association is of "Own the account" type (Administrator), you can do something like:
public class User
{
public int Id { get; set; }
public int Email { get; set; }
public virtual ICollection<AccountUserAssociation> Accounts { get; set; }
}
public class Account
{
public int Id { get; set; }
public virtual ICollection<AccountUserAssociation> Users { get; set; }
}
public class AccountUserAssociation
{
public virtual User User { get; set; }
public virtual Account Account { get; set; }
public AssociationType AssociationType { get; set; }
}
public enum AssociationType { Regular, Administrator }