Creating Your Own Filter

In some instances it can be useful to create your own filter for a project. In nearly all cases this should be an extension of the AndGroup or OrGroup class which 'auto' populates it's list of filters. Building a filter using groups of simpler filters maximises compatibility with Repositories ensuring good performance.

Group based filters

Imagine your project had a Contact, Order and Invoice models that all carried a set of address fields. Perhaps in your project you keep finding a requirement to select models that have a valid address, i.e. AddressLine1, City and Country all populated.

To avoid having to create a group of Not filters each time this is needed you could make your own filter that expressed this behaviour.

class AddressValid extends AndGroup
{
    public function __construct()
    {
        parent::__construct(
            new Not(new Equals("AddressLine1", ""),
            new Not(new Equals("City", ""),
            new Not(new Equals("Country", "")
        );
    }
}

$contacts = Contact::find(new AddressValid());
$invoices = Invoice::find(new AddressValid());
$orders = Order::find(new AddressValid());

Custom filters

If you need a more complex calculation that can't be easily constructed through basic filters and groups you may need to build your own custom filter. All filter objects extend the Filter base class so your first task is to extend it and then implement the evaluate() function. evaluate() should return true if you calculate the model in question should be removed (filtered) from the collection.

class StockMonths extends Filter
{
    public function evaluate(Model $model)
    {
        // Remove models where stock levels indicate it won't last another
        // month.
        if (($model->AverageUsagePerMonth / $model->StockLevel) < 1) {
            return true;
        } else {
            return false;
        }
    }
}

It's important to bear in mind however that a custom filter will have no repository support and will involve iterating over all the models in the collection to evaluate your filter.