title: Laravel hasone relation explain
body: <p><a href="https://i.stack.imgur.com/FMkpw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FMkpw.png" alt="enter image description here"></a></p>
  
  <p><strong>return $this->hasOne('App\Phone', 'foreign_key', 'local_key');</strong></p>
  
  <p>I need hasone relationship in these two tables.</p>
  
  <p>in both tables, the relation should be in between username column in both parent and child table, not id in parent and username or any other in child.
  Please explain 3rd parameter in above hasone function.</p>