Php – Inheritance when following the Repository Pattern in PHP

design-patternsinheritanceobject-oriented-designPHPrepository

I am trying to build a PHP application using the Repository Pattern but I'm not sure how I should implement the save method.

I have an abstract class called ItemRepository which have the following method:

abstract class ItemRepository
{
    public function save(Item $item);
}

Where Item also is an abstract class.

Now I want to implement the class MovieRepository which extends ItemRepository. Here I want to save instances of the Movie class which extends Item.

Though doing it like this in PHP

// MovieRepository.php
class MovieRepository extends ItemRepository
{
    public function save(Movie $movie)
    {
        ...        
    }
}

gives the following error

Declaration of MovieRepository::save() should be compatible with ItemRepository::save(Item $item)

What is the right way to do this?

Best Answer

Drop the Item/Movie types from the save() method:

abstract class ItemRepository
{
    public abstract function save($item);
}

class MovieRepository extends ItemRepository
{
    public function save($movie)
    {
        ...        
    }
}

PHP is primarily dynamically typed language and while I understand the desire to use types as much as possible, in this case PHP's type system is not strong enough to express what you need. In other languages (Java, C++), you could express it with generics, which PHP lacks.

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