title: inserting data in many to many relationship in entity framework
body: <p>I have two tables (users , messages) which there is many to many relationship for them.
  i want to add new messages in message table and allocate massages to current users.
  Also i insert data like below:</p>
  
  <pre><code>Message newMessage = Message.CreateMessage("MessageText", "DateTime");
  newMessage.Users.Add(new User{..... });
  context.SaveChange();
  </code></pre>
  
  <p>this code will execute a query which add a new user in users table while the users table has some specified users and i don't want to add new user but as i mentioned i want to add new messages in message table and allocate massages to current users.</p>
  
  <p>how should i do that?</p>