Wednesday, 8 August 2007

Association Callbacks

Similiar to the normal callbacks that hook into the lifecycle of an Active Record object, you can also define callbacks that get trigged when you add an object to or removing an object from a association collection. Example:
class Project
has_and_belongs_to_many :developers, :after_add => :evaluate_velocity

def evaluate_velocity(developer)

It’s possible to stack callbacks by passing them as an array.

Possible callbacks are: before_add, after_add, before_remove and after_remove.

Should any of the before_add callbacks throw an exception, the object does not get added to the collection. Same with the before_remove callbacks, if an exception is thrown the object doesn’t get removed.

1 comment:

Conroy Whitney said...

Very helpful, thank you!

Just to clarify for others, these callbacks belong in in the model on which you call update_attribute in the HABTM relationship, not for its partner model.

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