Question

Project hasMany Comments
Payment (id, project_id, value, date)

I want to include in my index view a column equal to the sum of payments per project. I want to be able to sort by this field.

I’ve found some similiar problems here but neither of them concerns pagination.

My current (wrong) solution:

    $this->paginate = array('Project' => array(
            'conditions' => array('Project.archived =' => $archive),
            'order' => 'Project.start_date DESC',
            'contain' => array(
                    'Payment' => array(
                            'fields' => array('SUM(Payment.value) as Project__value_sum'),
                            'group'  => array('Payment.project_id'),
                            )
                        )
        ));
    $data = $this->paginate('Project');
    $this->set('projects', $data);
    $this->set('archive', $archive);

Answer 1

Seems like you’ll probably want to do an afterSave on the Payment model.

Within the afterSave function, you run some MySQL that totals the payments (using MySQL SUM()) for the related Project, and store it in Project.payment_total.

Then, you can easily sort by that field, and it keeps you from having to run complex MySQL on every page, since it will only run when necessary (ie when there’s a new or changed payment)