title: Left Join CakePHP3
body: <p>I'm trying to do a LEFT JOIN in CakePHP3.
  But all I get is a "is not associated"-Error.</p>
  
  <p>I've two tables BORROWERS and IDENTITIES.
  In SQL this is what I want:</p>
  
  <pre><code>SELECT
   identities.id
  FROM
   identities
  LEFT JOIN borrowers ON borrowers.id = identities.id
  WHERE
   borrowers.id IS NULL;
  </code></pre>
  
  <p>I guess this is what I need:</p>
  
  <pre><code>$var = $identities-&gt;find()-&gt;select(['identities.id'])-&gt;leftJoinWith('Borrowers',
          function ($q) {
                 return $q-&gt;where(['borrowers.id' =&gt; 'identities.id']);
          });
  </code></pre>
  
  <p>But I'm getting "Identities is not associated with Borrowers".</p>
  
  <p>I also added this to my Identities Table:</p>
  
  <pre><code>$this-&gt;belongsTo('Borrowers', [
    'foreignKey' =&gt; 'id'
  ]);
  </code></pre>
  
  <p>What else do I need?
  Thanx!</p>