Freezable Behavior

, _(*1)

Freezable is a Jam ORM behavior for freezing dynamically computed values in the database., _(*2)

Often one would have a method in the model which computes and returns a value. It could be a price, time or anything else. The computation could be a heavy one or time sensitive (based on time, currency exchange rates and other). Then you would need to save the value in a database column (a.k.a freezing) and in the future read the value from the field rather than the method., _(*3)

The Freezable behavior allows you to do exactly that in an easy way. The freeze(), unfreeze() and is_frozen() methos give you the convenience to easily get either the dynamically computed or the frozen value when needed., _(*4)

Usage

It has 3 parameters associations, parent and fields, _(*5)

``` php class Some_Model extends Jam_Model {, _(*6)

public static function initialize(Jam_Meta $meta)
{
    $meta
        ->behaviors(array(
            'freezable' => Jam::behavior('freezable', array(
                'fields' => 'price',
                'parent' => 'some_parent_model',
                'associations' => array('some_child', 'some_children'),
            )),
        ));
}
//...

}, _(*7)


That means that whenever the model is *frozen* then the field named `price` will be assigned the value of the method `price()`.
And all the associations will be also *frozen*. The associations themselves have to be *freezable* (have the Freezable behavior attached) in order for this to work. And the `price()` method, as well as any other fields, have to take into account the value of the field. E.g.

``` php
public function price()
{
    return $this->price ? $this->price : $this->compute_price();
}

The parent association is used in order to find the value of is_frozen, so that only one model holds the value of the flag. So that if you call is_frozen() on a freezable that has a parent, then it will get that value from the parent., _(*8)