Phill Nacelli recently published an object factory on his blog. This started a conversation with
Nic Tunney and myself about Object Factories. We each took a different path in creating our own version of an Object Factory:
Phill’s Object Factory
Nic’s Object Factory
The goals for my object factory are:
- Simplify creation of objects: If the object factory isn’t making it easier to create objects in the rest of your code then something is wrong.
- Easy Configuration: This later became no configuration.
- Reusable: You should never have to edit the code in the cfc itself.
- Support singletons
Initializing the Factory
The factory takes the base cfc path as a required argument. This path is used to create objects and saves you from worrying about object paths in the rest of your code. The factory initialization also takes an unlimited number of key value pairs that will be used to initialize other objects. For instance many objects need a DSN for initialization either as a simple String or as DSN object. If the object factory is initialized with a DSN then the DSN object will automatically be passed into all object that have DSN as an argument. Currently this matching is based on name and not type, so following a standard naming convention in your init methods is required to use this factory. Here’s a sample of initializing the object factory with a DSN:
<cfset factory=createObject("component","#basepath#objectFactory").init(basePath,"DSN",DSN) />
Initialization Parameters
The getObject method retrieves an initialized object from the factory. You simply pass in the name off the object you wish to get. The factory introspecs the object using the getMetaData function and will automatically add in initialization arguments. Using the factory created above you could request an object that required the DSN without specifying it.
<cfcomponent displayname="MyObject" hint=" MyObject " output="false">
<cfset variables.DSN="" />
<cffunction name="init" displayname="Init" hint="Init" access="public" output="false">
<cfargument name="dsn" displayname="DSN" hint="Datasource" required="true">
<cfset variables.DSN=arguments.DSN />
<cfreturn this />
</cffunction>
</cfcomponent>
Code to get the object from the factory:
<cfset obj=factory.getObject("MyObject")>
The factory sees that the object has DNS as an argument and automatically adds it.
Additional Arguments
Objects may need additional arguments that aren’t auto populated. The getObject method takes the object name along with an unlimited number of key values pairs. The key value pairs are added to the argument collection for the object init. Arguments are automatically numbered according to the order in which they were passed to the method. Since we pass the object name as the first argument to getObject additional arguments are named numerically starting with 2.
<cfloop index="i" from="2" to="#ArrayLen(StructKeyArray(arguments))#" step="2">
<cfset objectParams[arguments[i]]=arguments[i+1] />
</cfloop>
Singletons
The factory supports singletons. Following my no configuration goal I wanted objects to be able to indicate they were singletons to the factory. This is accomplished by adding this.singleton=true to an object. This creates a public singleton property that the object factory can check. The factory checks to see if a singleton has already been created in the singleton cache, if it is in the cache the existing object is returned.
<cfif structKeyExists(variables.singletons,arguments.objectType)>
<cfreturn variables.singletons[arguments.objectType] />
</cfif>
Once a new object is created it is checked or a singleton property. If it exists and is true the object is added to the singleton cache. This will only happen the first time an object is initialized. If it was already in the cache the existing object would have been returned in the previous code.
<cfif StructKeyExists(objRet,"singleton") and objRet.singleton>
<cfset structInsert(variables.singletons,arguments.objectType,objRet,true) />
</cfif>
Over all I accomplished my goals. The object factory can be dropped into an application and supports all the functionality I wanted without needing any type of configuration or editing of the object factory code itself. It doesn’t have all the features of some other factories, but covers the functionality you need on a regular basis.
Download Object Factory and Sample Code
