title: What is this scala syntax: "users returning users.map(_._id)"
body: <p>Can anyone explain the 2nd to last line? What is <code>users returning...</code>? Thanks.</p>
  
  <pre><code>val users: TableQuery[Users] = TableQuery[Users]
  def create(data: Map[String, Any]): Int = {
    userId.withSession {
      implicit session =&gt;
        val userObj = new User(
        fullname = data("fullname").toString,
        username = data("username").toString,
        password = data("password").toString)
       (users returning users.map(_._id)) += userObj // What is this doing?
       0
    }
  }
  </code></pre>