$html->input('Model\nom_champ', array());

$html->input('Model.nom_champ', array());

<?php

class ConversationsController extends AppController
{

    var $name = 'Conversation';
    var $uses = array('Conversation', 'Assistance');
    
    function add()
    {
        if(isset($this->data))
        {
        $this->Conversation->set($this->data);
                if($this->Conversation->validates())
                {
                        $this->data = Sanitize::clean($this->data);
                        if($this->Conversation->saveAll($this->data))                                        // Inscription bdd réussie
                        {
                            debug($this->data);
                        } else {
                            $this->Session->setFlash("Une erreur s'est produite lors de l'ajout dans la base de données.");
                        }
                } else {
                        $this->Session->setFlash("Veuillez corriger les erreurs du formulaire.");
                        $this->validateErrors($this->Conversation);                                       // Erreur dans le formulaire, réaffichage
                }
        }
        $this->set('errors', $this->Conversation->validationErrors);
    }
}

<?php
class Assistance extends AppModel {

	var $name = 'Assistance';

	var $belongsTo = array(
		'Users' => array(
			'className' => 'Users',
			'foreignKey' => 'user_id',
			'conditions' => '',
			'fields' => '',
			'order' => ''
		)
        );
        var $hasMany = array(
                'Conversations' => array(
			'className' => 'Conversations',
			'foreignKey' => 'assistances_id',
			'conditions' => '',
			'fields' => '',
			'order' => ''
		)
	);

        var $_schema = array(
                "about" => array(
                    "type" => "string",
                    "length" => 255
                ),
                "knowledge" => array(
                    "type" => "select"
                ),
                "priority" => array(
                    "type" => "select"
                ),
                "message" => array(
                    "type" => "string",
                    "length" => 4000
                )
        );

        var $validate = array(
                "about" => array(
                    "notEmpty" => array(
                        "rule" => "notEmpty",
                        "message" => "Vous devez entrer un sujet pour votre demande."
                    ),
                    "between" => array(
                        "rule" => array('between', 10, 255),
                        "message" => "Le sujet de votre demande doit contenir au minimum 10 caractères."
                    )
                ),
                "message" => array(
                    "notEmpty" => array(
                        "rule" => "notEmpty",
                        "message" => "Le champ message ne doit pas rester vide."
                    ),
                    "between" => array(
                        "rule" => array('between', 50, 4000),
                        "message" => "Votre message doit contenir 50 caractères minimum."
                    )
                )
        );

}

<?php
    // Connecté, affichage du formulaire
    echo "<h3>Formulaire de demande d'assistance</h3>";
    echo $this->element('errors', array('errors' => $errors));
    echo $this->Form->create('Conversations', array('action' => 'add'));
    echo $this->Form->hidden('Assistances.users_id', array('value' => $session->read('Auth.User.id')));
    echo $this->Form->hidden('Conversation.users_id', array('value' => $session->read('Auth.User.id')));
    echo $this->Form->input('Assistances.about', array('label' => 'Sujet de la demande', 'error' => false));
    echo $html->tag('label', 'Vos connaissances', array('for' => 'UserKnowledge'));
    $options_list_connaissances = array('nulles' => 'Nulles', 'faibles' => 'Faibles', 'moyennes' => 'Moyennes', 'bonnes' => 'Bonnes', 'conséquentes' => 'Conséquentes');
    echo $this->Form->select('Assistances.knowledge', $options_list_connaissances, "moyennes", array("empty" => false));
    echo $html->tag('br');
    echo $html->tag('label', 'Priorité de la demande', array('for' => 'UserPriority'));
    $options_list_priorite = array('sansimportance' => 'Sans importance', 'faible' => 'Faible', 'moyenne' => 'Moyenne', 'urgente' => 'Urgente');
    echo $this->Form->select('Assistances.priority', $options_list_priorite, "sansimportance", array("empty" => false));
    echo $html->tag('br');
    echo $html->tag('label', 'Votre demande', array('for' => 'UserMessage'));
    echo $html->tag('br');
    echo $this->Form->textarea('Assistances.message', array("rows" => 8, "cols" => 60));
    echo $this->Form->end('Envoyer ma demande');
?>

create table blabla(
    id_blabla SERIAL NOT NULL,
    lib_blabla varchar(20),
 CONSTRAINT pk_1 PRIMARY KEY (id_blabla )
)

create table_t1(
   id_1 SERIAL NOT NULL,
   id_bla integer,
   lib_1 varchar(20)

 CONSTRAINT pk_1 PRIMARY KEY (id_1 ),
CONSTRAINT fk_1 FOREIGN KEY (id_bla) REFERENCES blabla(id_blabla )
)

create table_t2(
   id_2 SERIAL NOT NULL,
   id_bla2 integer,
   lib_2 varchar(20)

 CONSTRAINT pk_1 PRIMARY KEY (id_2 ),
CONSTRAINT fk_1 FOREIGN KEY (id_bla2 ) REFERENCES blabla(id_blabla )
)

var $belongsTo = array(
			'Blabla' =>
					array('className' => 'Blabla',
						'foreignKey' => 'id_bla',
						'conditions' => '',
						'fields' => '',
						'order' => '',
						'counterCache' => ''
						)
);

var $hasMany = array(
			'TableT1' =>
				array('className' => 'TableT1',
						'foreignKey' => 'id_blabla',
						'conditions' => '',
						'fields' => '',
						'order' => '',
						'limit' => '',
						'offset' => '',
						'dependent' => '',
						'exclusive' => '',
						'finderQuery' => '',
						'counterQuery' => ''
				),
			'TableT2' =>
				array('className' => 'TableT2',
						'foreignKey' => 'id_blabla',
						'conditions' => '',
						'fields' => '',
						'order' => '',
						'limit' => '',
						'offset' => '',
						'dependent' => '',
						'exclusive' => '',
						'finderQuery' => '',
						'counterQuery' => ''
				),

	);