aboutsummaryrefslogtreecommitdiffstats
path: root/activemodel/README.rdoc
blob: d9544673872a13ed42c1257bc0238864d48771b1 (plain) (blame)
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
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
= Active Model -- model interfaces for Rails

Active Model provides a known set of interfaces for usage in model classes.
They allow for Action Pack helpers to interact with non-Active Record models,
for example. Active Model also helps with building custom ORMs for use outside of
the Rails framework.

Prior to Rails 3.0, if a plugin or gem developer wanted to have an object
interact with Action Pack helpers, it was required to either copy chunks of
code from Rails, or monkey patch entire helpers to make them handle objects
that did not exactly conform to the Active Record interface. This would result
in code duplication and fragile applications that broke on upgrades. Active
Model solves this by defining an explicit API. You can read more about the
API in <tt>ActiveModel::Lint::Tests</tt>.

Active Model provides a default module that implements the basic API required
to integrate with Action Pack out of the box: <tt>ActiveModel::Model</tt>.

    class Person
      include ActiveModel::Model

      attr_accessor :name, :age
      validates_presence_of :name
    end

    person = Person.new(name: 'bob', age: '18')
    person.name   # => 'bob'
    person.age    # => '18'
    person.valid? # => true

It includes model name introspections, conversions, translations and
validations, resulting in a class suitable to be used with Action Pack.
See <tt>ActiveModel::Model</tt> for more examples.

Active Model also provides the following functionality to have ORM-like
behavior out of the box:

* Add attribute magic to objects

    class Person
      include ActiveModel::AttributeMethods

      attribute_method_prefix 'clear_'
      define_attribute_methods :name, :age

      attr_accessor :name, :age

      def clear_attribute(attr)
        send("#{attr}=", nil)
      end
    end

    person = Person.new
    person.clear_name
    person.clear_age

  {Learn more}[link:classes/ActiveModel/AttributeMethods.html]

* Callbacks for certain operations

    class Person
      extend ActiveModel::Callbacks
      define_model_callbacks :create

      def create
        run_callbacks :create do
          # Your create action methods here
        end
      end
    end

  This generates +before_create+, +around_create+ and +after_create+
  class methods that wrap your create method.

  {Learn more}[link:classes/ActiveModel/Callbacks.html]

* Tracking value changes

    class Person
      include ActiveModel::Dirty

      define_attribute_methods :name

      def name
        @name
      end

      def name=(val)
        name_will_change! unless val == @name
        @name = val
      end

      def save
        # do persistence work
        changes_applied
      end
    end

    person = Person.new
    person.name             # => nil
    person.changed?         # => false
    person.name = 'bob'
    person.changed?         # => true
    person.changed          # => ['name']
    person.changes          # => { 'name' => [nil, 'bob'] }
    person.save
    person.name = 'robert'
    person.save
    person.previous_changes # => {'name' => ['bob, 'robert']}

  {Learn more}[link:classes/ActiveModel/Dirty.html]

* Adding +errors+ interface to objects

  Exposing error messages allows objects to interact with Action Pack
  helpers seamlessly.

    class Person

      def initialize
        @errors = ActiveModel::Errors.new(self)
      end

      attr_accessor :name
      attr_reader   :errors

      def validate!
        errors.add(:name, "cannot be nil") if name.nil?
      end

      def self.human_attribute_name(attr, options = {})
        "Name"
      end
    end

    person = Person.new
    person.name = nil
    person.validate!
    person.errors.full_messages
    # => ["Name cannot be nil"]

  {Learn more}[link:classes/ActiveModel/Errors.html]

* Model name introspection

    class NamedPerson
      extend ActiveModel::Naming
    end

    NamedPerson.model_name.name   # => "NamedPerson"
    NamedPerson.model_name.human  # => "Named person"

  {Learn more}[link:classes/ActiveModel/Naming.html]

* Making objects serializable

  <tt>ActiveModel::Serialization</tt> provides a standard interface for your object
  to provide +to_json+ or +to_xml+ serialization.

    class SerialPerson
      include ActiveModel::Serialization

      attr_accessor :name

      def attributes
        {'name' => name}
      end
    end

    s = SerialPerson.new
    s.serializable_hash   # => {"name"=>nil}

    class SerialPerson
      include ActiveModel::Serializers::JSON
    end

    s = SerialPerson.new
    s.to_json             # => "{\"name\":null}"

    class SerialPerson
      include ActiveModel::Serializers::Xml
    end

    s = SerialPerson.new
    s.to_xml              # => "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<serial-person...

  {Learn more}[link:classes/ActiveModel/Serialization.html]

* Internationalization (i18n) support

    class Person
      extend ActiveModel::Translation
    end

    Person.human_attribute_name('my_attribute')
    # => "My attribute"

  {Learn more}[link:classes/ActiveModel/Translation.html]

* Validation support

    class Person
      include ActiveModel::Validations

      attr_accessor :first_name, :last_name

      validates_each :first_name, :last_name do |record, attr, value|
        record.errors.add attr, 'starts with z.' if value.to_s[0] == ?z
      end
    end

    person = Person.new
    person.first_name = 'zoolander'
    person.valid?  # => false

  {Learn more}[link:classes/ActiveModel/Validations.html]

* Custom validators

    class HasNameValidator < ActiveModel::Validator
      def validate(record)
        record.errors.add(:name, "must exist") if record.name.blank?
      end
    end

    class ValidatorPerson
      include ActiveModel::Validations
      validates_with HasNameValidator
      attr_accessor :name
    end

    p = ValidatorPerson.new
    p.valid?                  # =>  false
    p.errors.full_messages    # => ["Name must exist"]
    p.name = "Bob"
    p.valid?                  # =>  true

  {Learn more}[link:classes/ActiveModel/Validator.html]


== Download and installation

The latest version of Active Model can be installed with RubyGems:

  % gem install activemodel

Source code can be downloaded as part of the Rails project on GitHub

* https://github.com/rails/rails/tree/master/activemodel


== License

Active Model is released under the MIT license:

* http://www.opensource.org/licenses/MIT


== Support

API documentation is at

* http://api.rubyonrails.org

Bug reports can be filed for the Ruby on Rails project here:

* https://github.com/rails/rails/issues

Feature requests should be discussed on the rails-core mailing list here:

* https://groups.google.com/forum/?fromgroups#!forum/rubyonrails-core