The EF4 Sample

The Entity Framework 4.0 is a powful framework that used by entity to SQL. Here is a sample explain the many-to-many relationship.

The relationship is user and role. The User_Role is the table that save the relationship between user and role.

Some code snipes are :

        public void UpdateUser(DC.User user)
        {
            using (var context = GetContext())
            {
                var existUser = Get(context, user.Id);
                if (existUser == null)
                    throw new ApplicationException(string.Format("Update failed, user id: {0} didn't exist.", user.Id));
                UpdateUser(context, existUser, user.FromDataContract());
                //update roles
                UpdateRoles(context, user);
                context.SaveChanges();
            }
        }

        private void UpdateUser(SampleDBEntities context, User existUser, User user)
        {
            context.Users.Detach(existUser);
            context.Users.Attach(user);
            context.ObjectStateManager.ChangeObjectState(user, EntityState.Modified);
        }

        private void UpdateRoles(SampleDBEntities context, DC.User user)
        {
            var updateUser = Get(context, user.Id);
            var roles = user.Roles.FromDataContract();
            var intersectRoles = updateUser.Roles.Select(r => r.Id).Intersect(roles.Select(r => r.Id)).ToList();
            var removeRoles = updateUser.Roles.Select(r => r.Id).Except(intersectRoles).ToList();
            foreach (var roleId in removeRoles)
            {
                var oldRole = GetRole(context, roleId);
                if (oldRole == null)
                    throw new ApplicationException(string.Format("Update failed, role id: {0} didn't exist.", roleId));
                updateUser.Roles.Remove(oldRole);
            }

            var addRoles = roles.Select(r => r.Id).Except(intersectRoles).ToList();
            foreach (var roleId in addRoles)
            {
                var newRole = GetRole(context, roleId);
                if (newRole == null)
                    throw new ApplicationException(string.Format("Update failed, role id: {0} didn't exist.", roleId));
                updateUser.Roles.Add(newRole);
            }
        }

 The full code is here.