Forcing joins in a cakePHP find

Today I had to setup a complex find relation. Here is the simplifed version of what I had:

TABLE timestamps
int id
datetime date
string type
int user_id

The type field only had two types of values: START and END. As you can guess, this was used to log the time users where using an application. Every time a user started using the app, a START record was created, and when he loggued out, an END record was created. So basically, the records where working as pairs.

I wanted to get a list of all records that could be easily displayed. I wanted to bind the timestamp model to itself, so that when querying all the start records, I'll automatically have the end ones as related models.

Here's how I did that:

$this->find('all', array(
  'conditions' => array(
    'Timestamp.type' => 'START'
  ),
  'joins' => array(
    array(
      'table' => 'timestamp',
      'alias' => 'EndTimestamp',
      'type' => 'LEFT',
      'conditions' => array(
        'EndTimestamp.type' => 'END',
        'EndTimestamp.user_id = Timestamp.user_id',
        'EndTimestamp.date > Timestamp.date',
      )
    )
  ),
  'order' => array(
    'Timestamp.date' => 'ASC'
  ),
  'group' => 'Timestamp.date'
));

It will fetch all the start timestamp (fields) in chronological order (order). We will also define a custom join relation (joins). We set the table name and the alias we need, and set it as a JOIN LEFT.

Then we add the conditions: we want only the END records, that belongs to the same user, and that occurs after the START records. We also add a group key to make sure not to get twice the same result (or it will corrupt our results)

Note that the joins syntax needs to be wrapped in an unkeyed array. This is because you may need to add several joins.

I had never heard of this joins key before today, but it is quite handy, I guess I'll use it again.