gistfile1.aw

<?php
/**
 * belongsTo associations
 *
 * @var array
 */
	public $belongsTo = array(
		'Conta' => array(
			'className' => 'Conta',
			'foreignKey' => 'conta_id',
			'conditions' => '',
			'fields' => '',
			'order' => ''
		),
		'Categoria' => array(
			'className' => 'Categoria',
			'foreignKey' => 'categoria_id',
			'conditions' => '',
			'fields' => '',
			'order' => ''
		),
                /**
                 * Aqui esta o segredo
                 */
		'Banco' => array(
			'className' => 'Banco',
			'foreignKey' => false,
			'conditions' => 'Conta.banco_id = Banco.id',
			'fields' => '',
			'order' => ''
		)
	);