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Under Construction
This proposal is under construction and is not ready for review.

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Zend Framework: Zend_DI Component Proposal

Proposed Component Name Zend_DI
Developer Notes http://framework.zend.com/wiki/display/ZFDEV/Zend_DI
Proposers My E-mail Address
Revision 0.1 - 21 November 2007: Initial Proposal. (wiki revision: 40)

Table of Contents

1. Overview

Zend_DI is a dependency injector component. It minimizes coupling between groups of classes, makes unit testing much simpler, and provides an easy way to re-configure a package to use custom implementations of components. The architecture of the Zend_DI component is based on the following concepts:

  • Dependency injection is a technique that consists of passing objects via the constructor or setter methods.
  • The Container provides an easy way of re-configuring a package to use custom implementations of components.
  • Responsibility for object management is taken over by whatever container is being used to manage those objects.

Benefits of using a DI Container:

  • Easy best practice unit testing
  • Component reuse
  • Centralized configuration
  • Clean and declarative architecture
  • Maintainability and adaptability

2. References

3. Component Requirements, Constraints, and Acceptance Criteria

  • This component will use Reflection.

4. Dependencies on Other Framework Components

  • Zend_Config
  • Zend_Exception
  • Zend_Registry

5. Theory of Operation

Zend_DI provides generic factory classes that instantiate instances of classes. These instances are then configured by the container, allowing construction logic to be reused on a broader level. For example:

Once we separate configuration from use, we can easily test the Car with different Engines. It's just a matter of re-configuring the package and injecting Zend_Car_Parts_Engine_Gas instead of Zend_Car_Parts_Engine_Fuel.

6. Milestones / Tasks

  • Milestone 1: [DONE] Design interface
  • Milestone 2: [IN PROGRESS] Write proposal
  • Milestone 3: Gather feedback and revise design as necessary
  • Milestone 4: Develop full implementation and unit tests
  • Milestone 5: Documentation
  • Milestone 6: Future enhancements

7. Class Index

  • Zend_DI_Container
  • Zend_DI_Exception
  • Zend_DI_Container_Manager
  • Zend_DI_Container_Exception
  • Zend_DI_Component_Factory
  • Zend_DI_Component_Exception

8. Use Cases

The component handles injections via the constructor or setters methods. In addition, Zend_DI allows the user to map out specifications for components and their dependencies in a configuration file and generate the objects based on that specification. The configuration object can be set using the setConfig() method.

Lets assume we have the following classes:

Constructor dependency injection

The configuration array is typically set up in a different class. For example, each package can have its own configuration file, a PHP class or an XML file. The configuration file holds the components specifications and package dependencies.

UC-01

When you load a class, the constructor method (__construct) is selected by default.

UC-02
UC-03
UC-04
UC-05

Users can map out specifications for components and their dependencies.

If the user adds a value once $config['Foo']['constructor'] is set, an exception will be thrown:

Setter dependency injection

UC-06
UC-07
UC-08

Containers

You can tell Zend_DI what classes to manage by adding them to a container (the order of registration has no significance). Containers can be retrieved using the Zend_DI_Container_Manager::getContainer() method, which returns an instance of the Zend_Registry class.

UC-09

You can register your own container as long as you pass an instance of the Zend_Registry class. New containers can be register using the registerContainer() method.

UC-10

9. Class Skeletons

  • Zend_DI_Container
  • Zend_DI_Component_Factory
  • Zend_DI_Container_Manager

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