Class structure possibly needing implementation of composition to mimic multiple inheritance

Question

Here's the basic premise, I'm using an active record pattern for db objects, and I think I need some direction how to organize these classes. And also in general how I could potentially split up my class structure. Hopefully I don't explain this too terribly. If composition pattern is the way to go I may need a little hand holding on a way to implement it.

Let's say there's the ActiveRecord base class, at the bottom of the totem pole that deals with mapping objects to the db and the db to objects.

A child of ActiveRecord is a sort of generic User class, that deals with user sessions, logins, encryption of the password field on save and such.

Another child of ActiveRecord is a ActiveRecordButSlightlyMoreAdvanced class. Usually this class has nothing to do with User, but here's my issue.

I want to have a subclass that wants to be essentially a combination of User and ActiveRecordButSlightlyMoreAdvanced; UserButSlightlyMoreAdvanced, without having to copy paste all of the methods from User. It doesn't make sense for User to extend ActiveRecordButSlightlyMoreAdvanced, as it'd require essentially overriding a bunch of methods that have undesirable behavior for User. It would make sense for UserButSlightlyMoreAdvanced to extend ActiveRecordButSlightlyMoreAdvanced, but I'd have to copy and paste a bunch of methods from User.

I know some people think better with pictures, so here's the structure illustrated.

Base

class ActiveRecord
{
    ....
}

Child

class User extends ActiveRecord
{
    ....
}

Also Child

class ActiveRecordButSlightlyMoreAdvanced extends ActiveRecord
{
    ....
}

The Problem

class UserButSlightlyMoreAdvanced extends User AND ActiveRecordButSlightlyMoreAdvanced
{
        :( :( :(
}

I've been thinking about this problem for about a month now and cannot think of a solution that doesn't place burden of maintaining the objects dually if there's a change to how one of them implements saving. I'm going to experiment with a few solutions over the next couple of days and possibly post what I think was best in this situation.

ebadedude · Accepted Answer · 2012-10-11 21:44:50Z

1

My guess is that you meant to say this:

class UserButSlightlyMoreAdvanced extends User AND ActiveRecordButSlightlyMoreAdvanced 
{
    :) :) :)
}

If that is the case, look into traits http://php.net/manual/en/language.oop5.traits.php

answered Oct 11, 2012 at 21:44

ebadedude

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Anther Over a year ago

You're right ><. I feel like my slight typo destroyed my question a bit.

Joshua Kaiser · Accepted Answer · 2012-10-11 21:55:13Z

You might try using the strategy pattern. In this case you would create your class:

class UserButSlightlyMoreAdvanced extends ActiveRecord implements ActiveRecordButSlightlyMoreAdvancedStrategy
{
    private $_strategy;

    public function useStrategy(ActiveRecordButSlightlyMoreAdvancedStrategy $s) {
        $this->_strategy = $s;
    }
}

and make your strategy class:

interface ActiveRecordButSlightlyMoreAdvancedStrategy
{
        // Define what this should do here
}

Make a strategy class that implements the above interface.

class ActiveRecordButSlightlyMoreAdvanced implements ActiveRecordButSlightlyMoreAdvancedStrategry {
    // Do stuff here
}

Now when you call those advanced methods, both classes implement the same interface, but the UserButSlightlyMoreAdvanced class just passes the requests through to the strategy object:

class UserButSlightlyMoreAdvanced extends ActiveRecord implements ActiveRecordButSlightlyMoreAdvancedStrategy
    {
        private $_strategy;

        public function useStrategy(ActiveRecordButSlightlyMoreAdvancedStrategy $s) {
            $this->_strategy = $s;
        }

        public function someSlightlyMoreAdvancedFunction () {
             return $this->_strategy->someSlightlyMoreAdvancedFunction():
        }
    }

Hope that helps.

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