CakePHP mathematic-calculation field?

(Database structure like CakePHP select default value in SELECT input)

So, I have two tables in CakePHP: Trees, and Leafs. Every Leaf has a tree_id for its corresponding tree. Every leaf also has a numeric value. The default view that I baked for trees just lists all the trees in a table. Is there a way to add a dynamic column to that view's table that SUMS all the leafs of that tree and displays the sum in the table, as well as开发者_运维问答 another field showing the number of leafs a tree has?

example:

Leafs

Id   |  Tree Id  |  Leaf value
-----+-----------+---------------
24   |  1        | 19
70   |  1        | 33
121  |  1        | 30

Trees

Id   |  Tree  |  Number of leafs  |  Sum of leafs  |  Actions
-----+--------+-------------------+----------------+-------------------
1    |  foo   |  120              |  7270          |  View Edit Delete
2    |  bar   |  72               |  4028          |  View Edit Delete

Two ideas:

Fetch the summed field dynamically each time you need it using the Containable behavior, like (off the top of my head):

$this->Tree->find('all', array(
    ...
    'contain' => array(
        'Leaf' => array(
            'fields' => array('SUM(Leaf.value)'),
            'group'  => array('Leaf.tree_id')
        )
    )
);

Or create a new column in the Tree model like leaf_values and update it every time you change something in the Leaf model:

// Leaf model
function afterSave() {
    $sum = /* calculate sum */;
    $this->Tree->updateAll(
        array('Tree.leaf_values' => $sum),
        array('Tree.id' => $this->data['Leaf']['tree_id'])
    );
}

function afterDelete() {
    // same for afterDelete
}

I don't think you can use group within containable calls.