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PODependency-injection in real life
 

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    <p>I am building a really minimal MVC framework to increase my PHP knowledge and challenge myself. I've come to the point where Classes begin to be dependent on each other to work. <a href="http://fabien.potencier.org/article/11/what-is-dependency-injection" rel="nofollow noreferrer">Dependency injection</a> seems to be the solution to this and are used by some of the <a href="http://components.symfony-project.org/dependency-injection/" rel="nofollow noreferrer">big frameworks</a> around. </p> <p>I've found <a href="https://github.com/troelskn/bucket" rel="nofollow noreferrer">Bucket</a> on Github and have messed around it for a while to understand the basics. <strong>What I can't get my head around however is when it's appropriate to create a Container?</strong></p> <p>Making one big container including every possible class that <em>may be needed</em> seems nothing but counter-productive to me and I can't imagine that it is good practice. It seems like the recipe for bad performance at least.</p> <p>In the alternative, which is to make multiple containers, I still don't get how the ever-stinking Singletons are not needed anymore.</p> <p>Let's say that I would have the following code:</p> <pre><code>$session_container = new bucket_Container(); $session_container-&gt;create('Database'); $session_container-&gt;create('Database_Sessions'); $log_container = new bucket_Container(); $log_container-&gt;create('Database'); $log_container-&gt;create('Database_Log'); </code></pre> <p>So here we have two containers, or in this case <em>buckets</em> for two totally different usages which are mutual by their dependency on the <code>Database</code> class.</p> <p>My logic tells me that the above code will create two independent instances of the <code>Database</code>-class, meaning that I still would have to make the <code>Database</code>-class a singleton to ensure that concurrent instances of my database connection isn't occurring?</p> <p><strong>Is this correct?</strong></p>
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    1. COfrequently, you need only 1 container for your application.
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    2. COHi meze - please tell me why I would want that. Isn't the whole purpuse of OOP to make the code modular and thereby to only have the parts needed loaded and in action?
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    3. COYou need to read more on dependency injection. What you are doing is called service locator pattern, read the article written by Martin fowler about it http://martinfowler.com/articles/injection.html
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