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
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
|
require 'active_support/core_ext/class/attribute'
module ActiveRecord
# = Active Record Observer
#
# 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.
#
# class ContactObserver < ActiveRecord::Observer
# def after_create(contact)
# contact.logger.info('New contact added!')
# end
#
# def after_destroy(contact)
# contact.logger.warn("Contact with an id of #{contact.id} was destroyed!")
# end
# end
#
# This Observer uses logger to log when specific callbacks are triggered.
#
# == 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 which takes
# either the concrete class (Product) or a symbol for that class (:product):
#
# 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.
#
# == Storing Observers in Rails
#
# If you're using Active Record within Rails, observer classes are usually stored in app/models with the
# naming convention of app/models/audit_observer.rb.
#
# == Configuration
#
# In order to activate an observer, list it in the <tt>config.active_record.observers</tt> configuration setting in your
# <tt>config/application.rb</tt> file.
#
# config.active_record.observers = :comment_observer, :signup_observer
#
# Observers will not be invoked unless you define these in your application configuration.
#
# == Loading
#
# Observers register themselves in the model class they observe, since it is the class that
# notifies them of events when they occur. As a side-effect, when an observer is loaded its
# corresponding model class is loaded.
#
# Up to (and including) Rails 2.0.2 observers were instantiated between plugins and
# application initializers. Now observers are loaded after application initializers,
# so observed models can make use of extensions.
#
# If by any chance you are using observed models in the initialization you can still
# load their observers by calling <tt>ModelObserver.instance</tt> before. Observers are
# singletons and that call instantiates and registers them.
#
class Observer < ActiveModel::Observer
class_attribute :observed_methods
self.observed_methods = [].freeze
def initialize
super
observed_descendants.each { |klass| add_observer!(klass) }
end
def self.method_added(method)
method = method.to_sym
if ActiveRecord::Callbacks::CALLBACKS.include?(method)
self.observed_methods += [method]
self.observed_methods.freeze
end
end
protected
def observed_descendants
observed_classes.sum([]) { |klass| klass.descendants }
end
def observe_callbacks?
self.class.observed_methods.any?
end
def add_observer!(klass)
super
define_callbacks klass if observe_callbacks?
end
def define_callbacks(klass)
existing_methods = klass.instance_methods.map(&:to_sym)
observer = self
observer_name = observer.class.name.underscore.gsub('/', '__')
self.class.observed_methods.each do |method|
callback = :"_notify_#{observer_name}_for_#{method}"
unless existing_methods.include? callback
klass.send(:define_method, callback) do # def _notify_user_observer_for_before_save
observer.update(method, self) # observer.update(:before_save, self)
end # end
klass.send(method, callback) # before_save :_notify_user_observer_for_before_save
end
end
end
end
end
|
