Groovy 1.6 and Per-Instance Metaclass

Ivan Moscoso, Wednesday, February 25, 2009 @ 3:30 pm

Groovy
One of the new features of Groovy 1.6 includes support for per-instance metaclasses. This is a nice addition to the language, since it allows to change the behavior of objects without affecting all instances of the class as a whole.

For testing, it is often useful to mock out specific behavior of an object without affecting the class as a whole. While some mocking frameworks already allow this, they usually run through a few hoops (i.e. "partial mocks"). Allowing support directly in the language can simplify this kind of approach.

Another case where per-instance metaprogramming can be useful is in employing template patterns on a per-instance basis. Picture the case where the domain decides that one of its children is no longer in a valid state. Most domain models handle this by embedding some sort of state object within the children, so that any object holding a reference to the children know what the child can or can not do. With a per-instance metaclass, however, the aggregate root can simply add or replace behavior of that instance of the object alone.
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software development Software Development

acts_without_database: Leverage ActiveRecord with Non-Database Backed Objects

Anthony Caliendo, Monday, December 29, 2008 @ 2:53 pm

ActiveRecord comes with a lot of nice things that aren't really dependent on having a database backed model. The most obvious example of this is the validation framework baked into ActiveRecord. Also, there are several plugins which add some useful behavior to ActiveRecord objects but don't rely on having a database.

In the future, I believe the rails team aims to make certain things more modular and easier to pull out and use separately from ActiveRecord (validation being one of those). However, if you are working on a project which is locked into a certain version of rails or you're impatient, there is a very simple plugin which can solve your needs.

Enter acts_without_database...
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agile ajax Agile Ajax

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