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17 lines
1.2 KiB
Markdown
17 lines
1.2 KiB
Markdown
# Dependency Injection
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## Purpose
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To implement a loosely coupled architecture in order to get better testable, maintainable and extendable code.
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## Usage
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Configuration gets injected and `Connection` will get all that it needs from `$config`. Without DI, the configuration would be created directly in `Connection`, which is not very good for testing and extending `Connection`.
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Notice we are following Inversion of control principle in `Connection` by asking `$config` to implement `Parameters` interface. This decouples our components. We don't care where the source of information comes from, we only care that `$config` has certain methods to retrieve that information. Read more about Inversion of control [here](http://en.wikipedia.org/wiki/Inversion_of_control).
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## Examples
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* The Doctrine2 ORM uses dependency injection e.g. for configuration that is injected into a `Connection` object. For testing purposes, one can easily create a mock object of the configuration and inject that into the `Connection` object
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* Symfony and Zend Framework 2 already have containers for DI that create objects via a configuration array and inject them where needed (i.e. in Controllers)
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