aboutsummaryrefslogtreecommitdiffstats
path: root/activemodel/lib/active_model/attribute_methods.rb
blob: 817640b178cf4f3cb1c7d0d82b471e40ef3691c1 (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
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
require 'active_support/core_ext/hash/keys'
require 'active_support/core_ext/class/inheritable_attributes'

module ActiveModel
  class MissingAttributeError < NoMethodError
  end
  # == Active Model Attribute Methods
  #
  # <tt>ActiveModel::AttributeMethods</tt> provides a way to add prefixes and suffixes
  # to your methods as well as handling the creation of Active Record like class methods
  # such as +table_name+.
  # 
  # The requirements to implement ActiveModel::AttributeMethods are to:
  #
  # * <tt>include ActiveModel::AttributeMethods</tt> in your object
  # * Call each Attribute Method module method you want to add, such as 
  #   attribute_method_suffix or attribute_method_prefix
  # * Call <tt>define_attribute_methods</tt> after the other methods are
  #   called.
  # * Define the various generic +_attribute+ methods that you have declared
  # 
  # A minimal implementation could be:
  # 
  #   class Person
  #     include ActiveModel::AttributeMethods
  #     
  #     attribute_method_affix  :prefix => 'reset_', :suffix => '_to_default!'
  #     attribute_method_suffix '_contrived?'
  #     attribute_method_prefix 'clear_'
  #     define_attribute_methods ['name']
  #     
  #     attr_accessor :name
  #     
  #     private
  #     
  #     def attribute_contrived?(attr)
  #       true
  #     end
  #     
  #     def clear_attribute(attr)
  #       send("#{attr}=", nil)
  #     end
  #     
  #     def reset_attribute_to_default!(attr)
  #       send("#{attr}=", "Default Name")
  #     end
  #   end
  #
  # Notice that whenever you include ActiveModel::AttributeMethods in your class,
  # it requires you to implement a <tt>attributes</tt> methods which returns a hash 
  # with each attribute name in your model as hash key and the attribute value as 
  # hash value.
  #
  # Hash keys must be strings.
  #
  module AttributeMethods
    extend ActiveSupport::Concern

    module ClassMethods
      # Defines an "attribute" method (like +inheritance_column+ or +table_name+). 
      # A new (class) method will be created with the given name. If a value is 
      # specified, the new method will return that value (as a string). 
      # Otherwise, the given block will be used to compute the value of the 
      # method.
      #
      # The original method will be aliased, with the new name being prefixed
      # with "original_". This allows the new method to access the original 
      # value.
      #
      # Example:
      #
      #   class Person
      # 
      #     include ActiveModel::AttributeMethods
      # 
      #     cattr_accessor :primary_key
      #     cattr_accessor :inheritance_column
      #     
      #     define_attr_method :primary_key, "sysid"
      #     define_attr_method( :inheritance_column ) do
      #       original_inheritance_column + "_id"
      #     end
      # 
      #   end
      # 
      # Provides you with:
      # 
      #   AttributePerson.primary_key
      #   # => "sysid"
      #   AttributePerson.inheritance_column = 'address'
      #   AttributePerson.inheritance_column
      #   # => 'address_id'
      def define_attr_method(name, value=nil, &block)
        sing = singleton_class
        sing.class_eval <<-eorb, __FILE__, __LINE__ + 1
          if method_defined?(:original_#{name})
            undef :original_#{name}
          end
          alias_method :original_#{name}, :#{name}
        eorb
        if block_given?
          sing.send :define_method, name, &block
        else
          # use eval instead of a block to work around a memory leak in dev
          # mode in fcgi
          sing.class_eval <<-eorb, __FILE__, __LINE__ + 1
            def #{name}; #{value.to_s.inspect}; end
          eorb
        end
      end

      # Declares a method available for all attributes with the given prefix.
      # Uses +method_missing+ and <tt>respond_to?</tt> to rewrite the method.
      #
      #   #{prefix}#{attr}(*args, &block)
      #
      # to
      #
      #   #{prefix}attribute(#{attr}, *args, &block)
      #
      # An instance method <tt>#{prefix}attribute</tt> must exist and accept 
      # at least the +attr+ argument.
      #
      # For example:
      #
      #   class Person
      # 
      #     include ActiveModel::AttributeMethods
      #     attr_accessor :name
      #     attribute_method_prefix 'clear_'
      #     define_attribute_methods [:name]
      #
      #     private
      # 
      #     def clear_attribute(attr)
      #       send("#{attr}=", nil)
      #     end
      #   end
      #
      #   person = Person.new
      #   person.name = "Bob"
      #   person.name          # => "Bob"
      #   person.clear_name
      #   person.name          # => nil
      def attribute_method_prefix(*prefixes)
        attribute_method_matchers.concat(prefixes.map { |prefix| AttributeMethodMatcher.new :prefix => prefix })
        undefine_attribute_methods
      end

      # Declares a method available for all attributes with the given suffix.
      # Uses +method_missing+ and <tt>respond_to?</tt> to rewrite the method.
      #
      #   #{attr}#{suffix}(*args, &block)
      #
      # to
      #
      #   attribute#{suffix}(#{attr}, *args, &block)
      #
      # An <tt>attribute#{suffix}</tt> instance method must exist and accept at least
      # the +attr+ argument.
      #
      # For example:
      #
      #   class Person
      # 
      #     include ActiveModel::AttributeMethods
      #     attr_accessor :name
      #     attribute_method_suffix '_short?'
      #     define_attribute_methods [:name]
      #
      #     private
      # 
      #     def attribute_short?(attr)
      #       send(attr).length < 5
      #     end
      #   end
      #
      #   person = Person.new
      #   person.name = "Bob"
      #   person.name          # => "Bob"
      #   person.name_short?   # => true
      def attribute_method_suffix(*suffixes)
        attribute_method_matchers.concat(suffixes.map { |suffix| AttributeMethodMatcher.new :suffix => suffix })
        undefine_attribute_methods
      end

      # Declares a method available for all attributes with the given prefix
      # and suffix. Uses +method_missing+ and <tt>respond_to?</tt> to rewrite
      # the method.
      #
      #   #{prefix}#{attr}#{suffix}(*args, &block)
      #
      # to
      #
      #   #{prefix}attribute#{suffix}(#{attr}, *args, &block)
      #
      # An <tt>#{prefix}attribute#{suffix}</tt> instance method must exist and
      # accept at least the +attr+ argument.
      #
      # For example:
      #
      #   class Person
      # 
      #     include ActiveModel::AttributeMethods
      #     attr_accessor :name
      #     attribute_method_affix :prefix => 'reset_', :suffix => '_to_default!'
      #     define_attribute_methods [:name]
      #
      #     private
      # 
      #     def reset_attribute_to_default!(attr)
      #       ...
      #     end
      #   end
      #
      #   person = Person.new
      #   person.name                         # => 'Gem'
      #   person.reset_name_to_default!
      #   person.name                         # => 'Gemma'
      def attribute_method_affix(*affixes)
        attribute_method_matchers.concat(affixes.map { |affix| AttributeMethodMatcher.new :prefix => affix[:prefix], :suffix => affix[:suffix] })
        undefine_attribute_methods
      end

      def alias_attribute(new_name, old_name)
        attribute_method_matchers.each do |matcher|
          module_eval <<-STR, __FILE__, __LINE__ + 1
            def #{matcher.method_name(new_name)}(*args)
              send(:#{matcher.method_name(old_name)}, *args)
            end
          STR
        end
      end

      # Declares a the attributes that should be prefixed and suffixed by 
      # ActiveModel::AttributeMethods.
      # 
      # To use, pass in an array of attribute names (as strings or symbols),
      # be sure to declare +define_attribute_methods+ after you define any
      # prefix, suffix or affix methods, or they will not hook in.
      # 
      #   class Person
      # 
      #     include ActiveModel::AttributeMethods
      #     attr_accessor :name, :age, :address
      #     attribute_method_prefix 'clear_'
      #
      #     # Call to define_attribute_methods must appear after the
      #     # attribute_method_prefix, attribute_method_suffix or
      #     # attribute_method_affix declares.
      #     define_attribute_methods [:name, :age, :address]
      #
      #     private
      # 
      #     def clear_attribute(attr)
      #       ...
      #     end
      #   end
      def define_attribute_methods(attr_names)
        return if attribute_methods_generated?
        attr_names.each do |attr_name|
          attribute_method_matchers.each do |matcher|
            unless instance_method_already_implemented?(matcher.method_name(attr_name))
              generate_method = "define_method_#{matcher.prefix}attribute#{matcher.suffix}"

              if respond_to?(generate_method)
                send(generate_method, attr_name)
              else
                method_name = matcher.method_name(attr_name)

                generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
                  if method_defined?(:#{method_name})
                    undef :#{method_name}
                  end
                  def #{method_name}(*args)
                    send(:#{matcher.method_missing_target}, '#{attr_name}', *args)
                  end
                STR
              end
            end
          end
        end
        @attribute_methods_generated = true
      end

      # Removes all the preiously dynamically defined methods from the class
      def undefine_attribute_methods
        generated_attribute_methods.module_eval do
          instance_methods.each { |m| undef_method(m) }
        end
        @attribute_methods_generated = nil
      end

      # Returns true if the attribute methods defined have been generated.
      def generated_attribute_methods #:nodoc:
        @generated_attribute_methods ||= begin
          mod = Module.new
          include mod
          mod
        end
      end

      # Returns true if the attribute methods defined have been generated.
      def attribute_methods_generated?
        @attribute_methods_generated ||= nil
      end

      protected
        def instance_method_already_implemented?(method_name)
          method_defined?(method_name)
        end

      private
        class AttributeMethodMatcher
          attr_reader :prefix, :suffix

          AttributeMethodMatch = Struct.new(:target, :attr_name)

          def initialize(options = {})
            options.symbolize_keys!
            @prefix, @suffix = options[:prefix] || '', options[:suffix] || ''
            @regex = /^(#{Regexp.escape(@prefix)})(.+?)(#{Regexp.escape(@suffix)})$/
          end

          def match(method_name)
            if matchdata = @regex.match(method_name)
              AttributeMethodMatch.new(method_missing_target, matchdata[2])
            else
              nil
            end
          end

          def method_name(attr_name)
            "#{prefix}#{attr_name}#{suffix}"
          end

          def method_missing_target
            :"#{prefix}attribute#{suffix}"
          end
        end

        def attribute_method_matchers #:nodoc:
          read_inheritable_attribute(:attribute_method_matchers) || write_inheritable_attribute(:attribute_method_matchers, [])
        end
    end

    # Allows access to the object attributes, which are held in the 
    # <tt>@attributes</tt> hash, as though they were first-class methods. So a 
    # Person class with a name attribute can use Person#name and Person#name= 
    # and never directly use the attributes hash -- except for multiple assigns
    # with ActiveRecord#attributes=. A Milestone class can also ask 
    # Milestone#completed? to test that the completed attribute is not +nil+ 
    # or 0.
    #
    # It's also possible to instantiate related objects, so a Client class 
    # belonging to the clients table with a +master_id+ foreign key can 
    # instantiate master through Client#master.
    def method_missing(method_id, *args, &block)
      method_name = method_id.to_s
      if match = match_attribute_method?(method_name)
        guard_private_attribute_method!(method_name, args)
        return __send__(match.target, match.attr_name, *args, &block)
      end
      super
    end

    # A Person object with a name attribute can ask <tt>person.respond_to?(:name)</tt>,
    # <tt>person.respond_to?(:name=)</tt>, and <tt>person.respond_to?(:name?)</tt>
    # which will all return +true+.
    alias :respond_to_without_attributes? :respond_to?
    def respond_to?(method, include_private_methods = false)
      if super
        return true
      elsif !include_private_methods && super(method, true)
        # If we're here then we haven't found among non-private methods
        # but found among all methods. Which means that the given method is private.
        return false
      elsif match_attribute_method?(method.to_s)
        return true
      end
      super
    end

    protected
      def attribute_method?(attr_name)
        attributes.include?(attr_name)
      end

    private
      # Returns a struct representing the matching attribute method.
      # The struct's attributes are prefix, base and suffix.
      def match_attribute_method?(method_name)
        self.class.send(:attribute_method_matchers).each do |method|
          if (match = method.match(method_name)) && attribute_method?(match.attr_name)
            return match
          end
        end
        nil
      end

      # prevent method_missing from calling private methods with #send
      def guard_private_attribute_method!(method_name, args)
        if self.class.private_method_defined?(method_name)
          raise NoMethodError.new("Attempt to call private method", method_name, args)
        end
      end

      def missing_attribute(attr_name, stack)
        raise ActiveModel::MissingAttributeError, "missing attribute: #{attr_name}", stack
      end
  end
end