title: Grocery CRUD relation n_n - how to complete an other field in relational table
body: <p>I have an application where I use Codeigniter + Grocery CRUD.</p>
  
  <p>I was making a "n_n" relation , but in table that store the relation there is a third field.</p>
  
  <p>Bellow my DB structure:</p>
  
  <p><img src="https://i.stack.imgur.com/JDFhI.png" alt="enter image description here"></p>
  
  <p>Grocery CRUD allows me to select the socialmedia as displayed bellow:</p>
  
  <p><img src="https://i.stack.imgur.com/jrVbe.png" alt="enter image description here"></p>
  
  <p>The complete functionality is showed here: <a href="http://www.grocerycrud.com/documentation/options_functions/set_relation_n_n" rel="nofollow noreferrer">http://www.grocerycrud.com/documentation/options_functions/set_relation_n_n</a></p>
  
  <p>How can I complete the profile field (commerce_socialmedia.profile) when a socialmedia item is selected in my form?
  Someone can help me? Is there something already done for my necessity?</p>
  
  <p>Thanks</p>