Module | ActiveSupport::ClassMethods |
In: |
lib/active_support/callbacks.rb
|
Define sets of events in the object lifecycle that support callbacks.
define_callbacks :validate define_callbacks :initialize, :save, :destroy
define_callbacks :validate, :terminator => "result == false"
In this example, if any before validate callbacks returns false, other callbacks are not executed. Defaults to "false", meaning no value halts the chain.
class Audit def before(caller) puts 'Audit: before is called' end def before_save(caller) puts 'Audit: before_save is called' end end class Account include ActiveSupport::Callbacks define_callbacks :save set_callback :save, :before, Audit.new def save run_callbacks :save do puts 'save in main' end end end
In the above case whenever you save an account the method Audit#before will be called. On the other hand
define_callbacks :save, :scope => [:kind, :name]
would trigger Audit#before_save instead. That‘s constructed by calling #{kind}_#{name} on the given instance. In this case "kind" is "before" and "name" is "save". In this context +:kind+ and +:name+ have special meanings: +:kind+ refers to the kind of callback (before/after/around) and +:name+ refers to the method on which callbacks are being defined.
A declaration like
define_callbacks :save, :scope => [:name]
would call Audit#save.
Install a callback for the given event.
set_callback :save, :before, :before_meth set_callback :save, :after, :after_meth, :if => :condition set_callback :save, :around, lambda { |r| stuff; result = yield; stuff }
The second arguments indicates whether the callback is to be run +:before+, +:after+, or +:around+ the event. If omitted, +:before+ is assumed. This means the first example above can also be written as:
set_callback :save, :before_meth
The callback can specified as a symbol naming an instance method; as a proc, lambda, or block; as a string to be instance evaluated; or as an object that responds to a certain method determined by the :scope argument to define_callback.
If a proc, lambda, or block is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.
Before and around callbacks are called in the order that they are set; after callbacks are called in the reverse order.
Around callbacks can access the return value from the event, if it wasn‘t halted, from the yield call.
When creating or skipping callbacks, you can specify conditions that are always the same for a given key. For instance, in Action Pack, we convert :only and :except conditions into per-key conditions.
before_filter :authenticate, :except => "index"
becomes
set_callback :process_action, :before, :authenticate, :per_key => {:unless => proc {|c| c.action_name == "index"}}
Per-key conditions are evaluated only once per use of a given key. In the case of the above example, you would do:
run_callbacks(:process_action, action_name) { ... dispatch stuff ... }
In that case, each action_name would get its own compiled callback method that took into consideration the per_key conditions. This is a speed improvement for ActionPack.
Skip a previously set callback. Like set_callback, :if or :unless options may be passed in order to control when the callback is skipped.
class Writer < Person skip_callback :validate, :before, :check_membership, :if => lambda { self.age > 18 } end