Extend Core PHP Class instead of Dependency Injection?

Question

I am working on an application that will have a "library" folder which will contain a homemade framework/library (session, DB, cache,config type classes) and then a "modules" folder which will contain folders for the sections of my app (ie; blogs/, forums/, account/, etc,etc)

In most of my modules (blogs, forums, etc), I will need multiple objects like cache, database, logger, config objects. I was planning on using dependency injection for this but I am curious, couldn't I just have a Core class/object that could do stuff like my database, cache, logger, time, methods and then just extend this core class into my other module classes and have access to all these things without needing to inject them?

I am pretty new to using classes/object so I may be way off here, please explain.

Gordon · Accepted Answer · 2011-02-07 23:48:46Z

9

Classes should have a single responsibility. A Core class doing caching, db access, logging and time, etc is effectively a God Object aka The Blob. It's an AntiPattern. Don't do that. Make them SOLID.

edited Feb 7, 2011 at 23:48

answered Feb 7, 2011 at 23:43

Gordon

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deceze · Accepted Answer · 2011-02-07 23:49:36Z

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Extending classes makes sense if you specialize classes or, well, extend them.
It doesn't make sense and usually becomes messy if the extension has nothing to do with the original purpose of the base class.

For example, you may extend a DbBase class with a DbMySql class (specialization), or an HtmlHelper with an Html5Helper (extension).

You should not extend your DbClass into a ProductsModule. Both have nothing to do with each other. The ProductsModule is not inherently bound to a database, so you're mixing responsibilities that have nothing to do with each other.

answered Feb 7, 2011 at 23:49

deceze♦

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Loose Couplings · Accepted Answer · 2011-02-08 14:47:22Z

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I also agree with Gordon.

Personally I avoid the Factory static method approach. In essence, it's equivalent to using a global variable. It's the Service Locator anti-pattern.

In addition to the suggested DI container, I find manual dependency injection (i.e. with using a DI container) to be a valuable approach. There's no tool (i.e. container) that can design your classes to be loosely coupled, and I find that using manual DI is helpful for focusing on that.

[P.S. I would have added this as a comment, but I'm new and am unable to comment]

answered Feb 8, 2011 at 14:47

Loose Couplings

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Community · Accepted Answer · 2011-09-19 17:13:58Z

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What you CAN do, is creating a Factory class that instantiates and provides the single objects you need. Somthing like:

$db = myFactory::getDBO();
$conf = myFactory::getConfig();
$session = myFactory::getSession();

and so on.

edited Sep 19, 2011 at 17:13

CommunityBot

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answered Feb 7, 2011 at 23:50

david.wosnitza

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2 Comments

Gordon Over a year ago

A DI Container would be better suited, f.e. components.symfony-project.org/dependency-injection

david.wosnitza Over a year ago

@Gordon this is what I mean. In Joomla's Framework it's the Factory class that provides this services... it's even called JFactory :)

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