Child Injectors

Overview

Welcome to the world of hierarchical dependency injection. We had the ability before to add a parent injector to WireBox, but you can not only add a parent, but also many children to the hierarchy.

Every injector has the capability to store an ordered collection (ordered struct) of child injectors via the childInjectors property. Child injectors are used internally in many instances to provide a hierarchical approach to DI where instances can be searched for locally, in the parent and in the children.

Child Injector Methods

Here are some of the new methods to assist with child injectors:

• hasChildInjector( name ) - Verify if a child injector has been registered

• registerChildInjector( name, child ) - Register a child injector by name

• removeChildInjector( name ) - Remove a child injector by name

• getChildInjector( name ) - Get a child injector by name

• getChildInjectors() - Get all the child injectors registered

• getChildInjectorNames() - Get an array of all the registered child injectors

Child Enhanced Methods

• getInstance()

  • The getInstance()method has an injector argument so you can EXPLICITLY request an instance from a child injector by name getInstance( name : "service", injector : "childInjector" )

  • Apart from the explicit lookup it can also do implicit hierarchical lookups using the following order:

    • Locally

    • Parent

    • All Children (in order of registration)

• containsInstance( name ) - This method now also searches in the child collection for the specific name instance. The lookup searches in the following order:

  1. Locally

  2. Parent

  3. Children (in order of registration)

• shutdown() - The shutdown method has been enhanced to issue shutdown method calls to all child injectors registered.

Getting Instances From Specific Child Injectors

The getInstance() has been modified to have an injector argument that you can use to specifically ask for an instance from that child injector. If the child injector has not been registered you will get a InvalidChildInjector Exception.

getInstance( name: "CategoryService", injector : "ChildInjector" )

Child Injector Explicit DSL

The following is the DSL you can use to explicitly target a child injector for a dependency. You will prefix it with wirebox:child:{name} and the name of the injector:

// Use the property name as the instance name
property name="categoryService" inject="wirebox:child:childInjector"
// Use a specific instance name
property name="categoryService" inject="wirebox:child:childInjector:CategoryService"
// Use any DSL
property name="categoryService" inject="wirebox:child:childInjector:{DSL}"