Question

I have the following MySQL tables:

CREATE TABLE IF NOT EXISTS `conversations` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `user1_id` int(11) NOT NULL,
    `user2_id` int(11) NOT NULL,
    PRIMARY KEY (`id`),
    UNIQUE KEY `user1_id_2` (`user1_id`,`user2_id`)
);

CREATE TABLE IF NOT EXISTS `messages` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `conversation_id` int(11) NOT NULL,
    `sender_id` int(11) NOT NULL,
    `recipient_id` int(11) NOT NULL,
    `subject` varchar(64) NOT NULL,
    `body` text NOT NULL,
    `created` datetime DEFAULT NULL,
    `is_deleted_by_sender` tinyint(3) unsigned NOT NULL DEFAULT '0',
    `is_deleted_by_recipient` tinyint(3) unsigned NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`)
);

Note: In conversations table user1_id is less or equal to user2_id.

I want to get a list of conversations of a user X, where each conversation is displayed by the last message that has not been deleted by user X in that conversation, and paginate the result. (just like facebook messages. no matter the last message has been sent by X or the other user, it is shown as the display message.

I came up to the group-wise maximum solution which helped me create the following sub-query:

SELECT MAX(SubTable.id) AS id, conversation_id 
FROM newtravel.messages AS SubTable
WHERE (
((SubTable.sender_id = 9) AND (SubTable.is_deleted_by_sender = 0))
OR 
((SubTable.recipient_id = 9) AND (SubTable.is_deleted_by_recipient = 0))
)
GROUP BY conversation_id

Can we use this sub-query as a join table in $this->Paginator->settings array? If the answer is yes, it should generate a query like the following:

SELECT m1.id, m1.conversation_id, m1.body, m1.sender_id, m1.recipient_id
FROM messages m1
INNER JOIN ( THE_SUB_QUERY_ABOVE ) m2 
ON ( m1.conversation_id = m2.conversation_id
AND m1.id = m2.id ) 
ORDER BY m1.id DESC 

This final query returns the wanted results. But I couldn’t figure out a way to set the right options in the PaginatorComponent. The official documentation is insufficient for this kind of query. So, how can we configure the find conditions, joins, sub-queries, etc. in this situation?

Answer 1

Alright. I’ve solved this problem as follows:

$this->Message->Behaviors->attach('Containable');

$conditionsSubQuery = array(
    'OR' => array(
        array(
            'SubTable.sender_id' => $this->Auth->user('id'),
            'SubTable.is_deleted_by_sender' => 0
        ),
        array(
            'SubTable.recipient_id' => $this->Auth->user('id'),
            'SubTable.is_deleted_by_recipient' => 0
        )
    )
);

$db = $this->Message->getDataSource();
$subQuery = $db->buildStatement(
        array(
    'fields' => array('MAX(id)'),
    'table' => $db->fullTableName($this->Message),
    'alias' => 'SubTable',
    'limit' => null,
    'offset' => null,
    'joins' => array(),
    'conditions' => $conditionsSubQuery,
    'order' => null,
    'group' => 'conversation_id',
        ), $this->Message
);

$subQuery = ' Message.id IN (' . $subQuery . ') ';

$this->Paginator->settings = array(
    'Message' => array(
        'limit' => 5,
        'maxLimit' => 5,
        'contain' => array(
            'Sender' => array(
                'id', 'name', 'is_online', 'profile_image', 'thumbnail'
            ),
            'Recipient' => array(
                'id', 'name', 'is_online', 'profile_image', 'thumbnail'
            ),
            'Conversation'
        ),
        'order' => 'Message.id DESC'
    )
);

$this->set('conversations', $this->Paginator->paginate('Message', $subQuery));

Note that “Message” belongsTo “Sender” and “Recipient”, which are aliases for “users” table.