title: Name of primary key column is always id when using Laravel 5.3?
body: <p>Let say I have a table with table structure as following:</p>
  
  <pre><code>Table_A
      sid (auto increment, primary)
      .... some other column ....
      created_at (created using laravel eloquent timestamps() function)
      updated_at (same as above)
  </code></pre>
  
  <p>Then, I created a new column by.</p>
  
  <pre><code>$new_row = new TableA; //TableA is a model created pointing to Table_A
  $new_row-&gt;col1 = 'Some value';
  $new_row-&gt;col2 = 'Some other value';
  // Some other field
  $new_row-&gt;save()
  </code></pre>
  
  <p>Then, right after this section of code,</p>
  
  <pre><code>dd($new_row-&gt;sid);
  </code></pre>
  
  <p>Surprisingly, the output is:</p>
  
  <pre><code>null
  </code></pre>
  
  <p>However, when I change it to:</p>
  
  <pre><code>dd($new_row-&gt;id);
  </code></pre>
  
  <p>It returns the sid (i.e. the primary key value of the row). Is the name of the primary key always id when I am using auto-increment as my primary key in Laravel Model? Or why am I only getting the value when I use the name <code>id</code>?</p>
  
  <hr>
  
  <p>P.S. Let me make myself clear: I know how I can get the primary key value, and I know I can set the name of primary key in model. What I want to know is if this behavior holds for all primary key, or just those with primary key. </p>