Wednesday, October 10, 2007

Flex needs a Custom Metadata Class

At MAX, I was really surprised to find out a sekret Flex compiler feature: You can keep custom metadata around in your Flex app. There's a tutorial with a really sweet proposed application for that feature at Christophe Coenraets' Blog.

The only thing about that example is that the entityManager needs to know to read the objects passed into its save() method for metadata. That's not a problem for that use case. BTW, you can read metadata with describeType()

What if I wanted to copy more of the JPA with Flex? Then I'd need the FPA (a mythical Flex Persistence API) to manage the instantiation of the EntityManager and pass in a reference at runtime. I'd need to inject the right EntityManager into any code that wanted it. Right now to do something like that we'd need to read every class, or intelligently read certain classes, to figure out if there were annotations to deal with.

It'd be nicer if we had a first-class Metadata class that got instantiated by the framework at runtime and knew about the class it decorated. That way it could do things like negotiating with the "FPA" to get the right EntityManager at runtime based on configuration data. It could then modify the object that had the metadata with no developer intervention. It'd look something like this, following Christophe's example:

public var entityManager:EntityManager;

That would mean that at runtime, the 'applicationPersistenceContext' persistence context, which could contain data about which database in SQLLite to use, maybe usernames and passwords or something like that... in short: configuration you don't want compiled into your code. That PersistenceContext object would know to inject the correct EntityManager into the variable 'entityManager'.

I think it'd be a great addition to the framework which would allow a lot more use of the "Dependency Injection Pattern" to help make easy to use frameworks for specific needs on top of Flex.

I've created an enhancement issue here: If you agree, make sure you vote on the issue.

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