title: Validate multiple models in single Form
body: <p>I have to validate multiple model in single form using 'CakePHP'.
  I have 2 models.</p>
  
  <p><strong>Invoice</strong> </p>
  
  <pre><code>public $validate = array(
          'type' =&gt; array(
              'rule' =&gt;'notEmpty',
              'message' =&gt; 'Select Invoice Type.',
              'required' =&gt; true
          ),
          'number' =&gt; array(
              'rule' =&gt;'numeric',
              'message' =&gt; 'Enter Invoice Number.',
              'required' =&gt; true
          ),
          'date' =&gt; array(
              'rule' =&gt; array('date', 'dmy'),
              'allowEmpty' =&gt; true,
              'message' =&gt; 'Enter Invoice Date.'
          ),
      );
  
      public $belongsTo = array(
          'Client' =&gt; array(
              'className' =&gt; 'Client',
              'foreignKey' =&gt; 'client_id'
          ));
  </code></pre>
  
  <p><strong>Client</strong></p>
  
  <pre><code>public $validate = array(
          'name' =&gt; array(
              'rule' =&gt;'notEmpty',
              'message' =&gt; 'Enter Your Name.',
              'required' =&gt; true
          ),
          'company' =&gt; array(
              'rule' =&gt;'notEmpty',
              'message' =&gt; 'Enter Your Company Name.',
              'required' =&gt; true
          ),
          'address' =&gt; array(
              'rule' =&gt;'notEmpty',
              'message' =&gt; 'Enter Your address.',
              'required' =&gt; true
          )
      );
  
      public $hasMany = 'Invoice';
  </code></pre>
  
  <p>And I have one form with Fields like '<em>clientName</em>', '<em>Address</em>', '<em>InvoiceNumber</em>' and '<em>InvoiceDate</em>'.
  I have used saveAll(), but it is only validating <code>Invoice</code> data and not the <code>Client</code> data.</p>