title: Multiple business rules per Table in Cakephp
body: <p>On tables, we can have many different validations that we can call however we want:</p>
  
  <pre><code>public function validationDefault(Validator $validator)
  {
      $validator
          -&gt;requirePresence('title', 'create')
          -&gt;notEmpty('title');
  
      $validator
          -&gt;allowEmpty('link')
          -&gt;add('link', 'valid-url', ['rule' =&gt; 'url']);
  
      ...
  
      return $validator;
  }
  
  public function validationUpdate($validator)
  {
      $validator
          -&gt;add('title', 'notEmpty', [
              'rule' =&gt; 'notEmpty',
              'message' =&gt; __('You need to provide a title'),
          ])
          -&gt;add('body', 'notEmpty', [
              'rule' =&gt; 'notEmpty',
              'message' =&gt; __('A body is required')
          ]);
      return $validator;
  }
  </code></pre>
  
  <p>And then we can call it like:</p>
  
  <pre><code>$article = $articles-&gt;newEntity(
      $this-&gt;request-&gt;getData(),
      ['validate' =&gt; 'update']
  );
  </code></pre>
  
  <p>My problem is, that I'm building a custom shopping cart, and I want to check if the user has products in it, thus fitting as a business rule rather than data validation. But I need to call it "by hand" (e.g. not through <code>save()</code> action) as I only need to check it in some places that don't alter user data. 
  And, as for business rules, the only example provided in the book is just to put them in the <code>buildRules()</code> method.</p>
  
  <p>So, is there a way to have multiple business rules like how validating data is done, and call it "by hand"?</p>