ADO.net - Complex Data binding

Question

I am dealing with a problem i cannot solve by myself. I also tried to find out a solution on the net, without success.

Here the details ...

Its about a complex data binding (in this case , 3 database tables).

Here the tables i have (abstraction), trying to modelate a Users/Groups association

Table 1 - tblUsers
------------------------------
field1: Id
field2: Username
field3: Password

Table 2 - tblGroups
------------------------------
field1: Id
field2: GroupName
field3: Description

Table 3 - tblUsers_Groups
------------------------------
field1: Id
field2: Id_tblUsers
field3: Id_tblGroups

This way a single user can belong to multiples groups (and vice)

I have been trying to create a WinForm, like the Master - Detail kind, where the Master Grid should show the Users in tblUsers, and ... according to what I select there, show in the Details Grid, the groups the users selected belongs to ... but using the info in tblGroups

Could someone please give me a hand on this problem?

Answer 1

First table 3 should not have and ID
Use a composite key of Id_tblUsers, Id_tblGroups

In .NET the way I do it is

    public class UserGroup : Object
    {   // NO editing just add remove
        public User User { get; private set; }
        public Group Group { get; private set; }
        public override bool Equals(Object obj)
        {
            //Check for null and compare run-time types.
            if (obj == null || !(obj is UserGroup)) return false;
            UserGroup item = (UserGroup)obj;
            return (User.ID == item.User.ID && Group.ID == item.Group.ID);
        }
        public override int GetHashCode() { return (User.ID & 0xffff) + (Group.ID << 16); }
        public UserGroup(User user, Group group)
        { User = user; Group = group; }
    }

Create a HashSet of UsersGroups and pass it to both Group and User in the ctor.
It is just a reference to an object so everyone is referencing the same data.
Override GetHash for efficiency and Equals so cannot have a duplicate UserGroup in the HashSet.

The is the code for returning the groups a user is in

public List<Group> Groups
{   get { return usersGroups.Where(x => x.User == this)
                            .Select(x => x.Group)
                            .OrderBy(y => y.Name)
                            .ToList(); } }

Then the sister in Group to return users.

It may seem complex but what is cool is a single master. So when you revise HashSet of UserGroup it is reflected in both User and Group