1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
require 'singleton'
module ActiveRecord
# Observer classes respond to lifecycle callbacks to implement trigger-like
# behavior outside the original class. This is a great way to reduce the
# clutter that normally comes when the model class is burdened with
# functionality that doesn't pertain to the core responsibility of the
# class. Example:
#
# class CommentObserver < ActiveRecord::Observer
# def after_save(comment)
# Notifications.deliver_comment("admin@do.com", "New comment was posted", comment)
# end
# end
#
# This Observer sends an email when a Comment#save is finished.
#
# == Observing a class that can't be inferred
#
# Observers will by default be mapped to the class with which they share a name. So CommentObserver will
# be tied to observing Comment, ProductManagerObserver to ProductManager, and so on. If you want to name your observer
# differently than the class you're interested in observing, you can use the Observer.observe class method:
#
# class AuditObserver < ActiveRecord::Observer
# observe Account
#
# def after_update(account)
# AuditTrail.new(account, "UPDATED")
# end
# end
#
# If the audit observer needs to watch more than one kind of object, this can be specified with multiple arguments:
#
# class AuditObserver < ActiveRecord::Observer
# observe Account, Balance
#
# def after_update(record)
# AuditTrail.new(record, "UPDATED")
# end
# end
#
# The AuditObserver will now act on both updates to Account and Balance by treating them both as records.
#
# == Available callback methods
#
# The observer can implement callback methods for each of the methods described in the Callbacks module.
#
# == Triggering Observers
#
# In order to activate an observer, you need to call Observer.instance. In Rails, this can be done in controllers
# using the short-hand of for example observer :comment_observer.
class Observer
include Singleton
# Attaches the observer to the supplied model classes.
def self.observe(*models)
define_method(:observed_class) { models }
end
def initialize
[ observed_class ].flatten.each do |klass|
klass.add_observer(self)
klass.send(:define_method, :after_find) unless klass.respond_to?(:after_find)
end
end
def update(callback_method, object) #:nodoc:
send(callback_method, object) if respond_to?(callback_method)
end
private
def observed_class
if self.class.respond_to? "observed_class"
self.class.observed_class
else
Object.const_get(infer_observed_class_name)
end
end
def infer_observed_class_name
self.class.name.scan(/(.*)Observer/)[0][0]
end
end
end
|
