The EF4.1 Sample

The Entity Framework 4.1 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(User user)
        {
            UpdateUsers(user);
            UpdateRoles(user);
        }

        private void UpdateUsers(User user)
        {
            using (var context = GetContext())
            {
                context.Users.Attach(user);
                context.Entry(user).State = EntityState.Modified;
                context.SaveChanges();
            }
        }


        private void UpdateRoles(User user)
        {
            using (var context = GetContext())
            {
                var userToUpdate = GetUser(context, user.Id);
                if (userToUpdate == null)
                    throw new ApplicationException(string.Format("Update failed, user id: {0} didn't exist.", user.Id));

                var roles = user.Roles;
                var intersectRoles = userToUpdate.Roles.Select(r => r.Id).Intersect(roles.Select(r => r.Id)).ToList();
                var removeRoles = userToUpdate.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));
                    userToUpdate.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));
                    userToUpdate.Roles.Add(newRole);
                }
                context.SaveChanges();
            }
        }

 

The full code is here.

The improve version code is add the enum that indicate the action of insert or modify.

    public enum ActionCode
    {
        Inserted,
        Updated,
        Deleted
    };

 

After improve code is:

        private void UpdateProducts(Category category)
        {
            using (var context = GetContext())
            {
                var categoryToUpdate = GetCategory(context, category.CategoryId);
                if (categoryToUpdate == null)
                    throw new ApplicationException(string.Format("Update failed, user id: {0} didn't exist.", category.CategoryId));


                foreach (var productToUpdate in category.Products)
                {
                    switch (productToUpdate.ActionCode)
                    {
                        case ActionCode.Inserted:
                            productToUpdate.Category = categoryToUpdate;
                            context.Products.Add(productToUpdate);
                            break;
                        case ActionCode.Updated:
                            var oldProduct = GetProduct(context, productToUpdate.ProductId);
                            context.Entry(oldProduct).CurrentValues.SetValues(productToUpdate);
                            break;
                        case ActionCode.Deleted:
                            if (context.Entry(productToUpdate).State == EntityState.Detached)
                                context.Products.Attach(productToUpdate);
                            context.Products.Remove(productToUpdate);
                            break;
                    }
                }

                context.SaveChanges();
            }
        }

 The full code is here.