title: findAll by multiple conditions
body: <p>I have 4 tables:</p>
  
  <ul>
  <li>content</li>
  <li>relation</li>
  <li>subject</li>
  <li>group</li>
  </ul>
  
  <p>content:</p>
  
  <pre><code>id(int)
  title(varchar)
  text(text)
  </code></pre>
  
  <p>subject:</p>
  
  <pre><code>id(int)
  title(varchar)
  prent_id(int)
  </code></pre>
  
  <p>group:</p>
  
  <pre><code>id(int)
  title(varchar)
  </code></pre>
  
  <p>relation:</p>
  
  <pre><code>id(int)
  content_id(int)
  group_id(int)
  subject_id(int)
  </code></pre>
  
  <p><strong>relation</strong> to <strong>content</strong> is <strong>many to many</strong>.</p>
  
  <p><strong>group</strong> to <strong>content</strong> is <strong>many to many</strong>.</p>
  
  <p><strong>subject</strong> to <strong>content</strong> is <strong>many to many</strong>.</p>
  
  <p>Content may belong to several subjects or several groups.</p>
  
  <p>I want to execute a query somewhat like this:</p>
  
  <pre><code>select * from relation where group_id = 1,3 and subject_id = 1,4,6,7
  </code></pre>