aboutsummaryrefslogtreecommitdiffstats
path: root/activesupport/lib/active_support/callbacks.rb
blob: 656cba625cd828492112f06a00c5f4044710251e (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
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
require 'active_support/concern'
require 'active_support/descendants_tracker'
require 'active_support/core_ext/array/wrap'
require 'active_support/core_ext/class/attribute'
require 'active_support/core_ext/kernel/reporting'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/object/inclusion'

module ActiveSupport
  # \Callbacks are code hooks that are run at key points in an object's lifecycle.
  # The typical use case is to have a base class define a set of callbacks relevant
  # to the other functionality it supplies, so that subclasses can install callbacks
  # that enhance or modify the base functionality without needing to override
  # or redefine methods of the base class.
  #
  # Mixing in this module allows you to define the events in the object's lifecycle
  # that will support callbacks (via +ClassMethods.define_callbacks+), set the instance
  # methods, procs, or callback objects to be called (via +ClassMethods.set_callback+),
  # and run the installed callbacks at the appropriate times (via +run_callbacks+).
  #
  # Three kinds of callbacks are supported: before callbacks, run before a certain event;
  # after callbacks, run after the event; and around callbacks, blocks that surround the
  # event, triggering it when they yield. Callback code can be contained in instance
  # methods, procs or lambdas, or callback objects that respond to certain predetermined
  # methods. See +ClassMethods.set_callback+ for details.
  #
  # ==== Example
  #
  #   class Record
  #     include ActiveSupport::Callbacks
  #     define_callbacks :save
  #
  #     def save
  #       run_callbacks :save do
  #         puts "- save"
  #       end
  #     end
  #   end
  #
  #   class PersonRecord < Record
  #     set_callback :save, :before, :saving_message
  #     def saving_message
  #       puts "saving..."
  #     end
  #
  #     set_callback :save, :after do |object|
  #       puts "saved"
  #     end
  #   end
  #
  #   person = PersonRecord.new
  #   person.save
  #
  # Output:
  #   saving...
  #   - save
  #   saved
  #
  module Callbacks
    extend Concern

    included do
      extend ActiveSupport::DescendantsTracker
    end

    # Runs the callbacks for the given event.
    #
    # Calls the before and around callbacks in the order they were set, yields
    # the block (if given one), and then runs the after callbacks in reverse order.
    # Optionally accepts a key, which will be used to compile an optimized callback
    # method for each key. See +ClassMethods.define_callbacks+ for more information.
    #
    # If the callback chain was halted, returns +false+. Otherwise returns the result
    # of the block, or +true+ if no block is given.
    #
    #   run_callbacks :save do
    #     save
    #   end
    #
    def run_callbacks(kind, *args, &block)
      send("_run_#{kind}_callbacks", *args, &block)
    end

    class Callback #:nodoc:#
      @@_callback_sequence = 0

      attr_accessor :chain, :filter, :kind, :options, :per_key, :klass, :raw_filter

      def initialize(chain, filter, kind, options, klass)
        @chain, @kind, @klass = chain, kind, klass
        normalize_options!(options)

        @per_key              = options.delete(:per_key)
        @raw_filter, @options = filter, options
        @filter               = _compile_filter(filter)
        @compiled_options     = _compile_options(options)
        @callback_id          = next_id

        _compile_per_key_options
      end

      def clone(chain, klass)
        obj                  = super()
        obj.chain            = chain
        obj.klass            = klass
        obj.per_key          = @per_key.dup
        obj.options          = @options.dup
        obj.per_key[:if]     = @per_key[:if].dup
        obj.per_key[:unless] = @per_key[:unless].dup
        obj.options[:if]     = @options[:if].dup
        obj.options[:unless] = @options[:unless].dup
        obj
      end

      def normalize_options!(options)
        options[:if] = Array.wrap(options[:if])
        options[:unless] = Array.wrap(options[:unless])

        options[:per_key] ||= {}
        options[:per_key][:if] = Array.wrap(options[:per_key][:if])
        options[:per_key][:unless] = Array.wrap(options[:per_key][:unless])
      end

      def name
        chain.name
      end

      def next_id
        @@_callback_sequence += 1
      end

      def matches?(_kind, _filter)
        @kind == _kind && @filter == _filter
      end

      def _update_filter(filter_options, new_options)
        filter_options[:if].push(new_options[:unless]) if new_options.key?(:unless)
        filter_options[:unless].push(new_options[:if]) if new_options.key?(:if)
      end

      def recompile!(_options, _per_key)
        _update_filter(self.options, _options)
        _update_filter(self.per_key, _per_key)

        @callback_id      = next_id
        @filter           = _compile_filter(@raw_filter)
        @compiled_options = _compile_options(@options)
                            _compile_per_key_options
      end

      def _compile_per_key_options
        key_options  = _compile_options(@per_key)

        @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
          def _one_time_conditions_valid_#{@callback_id}?
            true #{key_options[0]}
          end
        RUBY_EVAL
      end

      # This will supply contents for before and around filters, and no
      # contents for after filters (for the forward pass).
      def start(key=nil, object=nil)
        return if key && !object.send("_one_time_conditions_valid_#{@callback_id}?")

        # options[0] is the compiled form of supplied conditions
        # options[1] is the "end" for the conditional
        #
        case @kind
        when :before
          # if condition    # before_save :filter_name, :if => :condition
          #   filter_name
          # end
          filter = <<-RUBY_EVAL
            unless halted
              # This double assignment is to prevent warnings in 1.9.3.  I would
              # remove the `result` variable, but apparently some other
              # generated code is depending on this variable being set sometimes
              # and sometimes not.
              result = result = #{@filter}
              halted = (#{chain.config[:terminator]})
            end
          RUBY_EVAL

          [@compiled_options[0], filter, @compiled_options[1]].compact.join("\n")
        when :around
          # Compile around filters with conditions into proxy methods
          # that contain the conditions.
          #
          # For `around_save :filter_name, :if => :condition':
          #
          # def _conditional_callback_save_17
          #   if condition
          #     filter_name do
          #       yield self
          #     end
          #   else
          #     yield self
          #   end
          # end
          #
          name = "_conditional_callback_#{@kind}_#{next_id}"
          @klass.class_eval <<-RUBY_EVAL,  __FILE__, __LINE__ + 1
             def #{name}(halted)
              #{@compiled_options[0] || "if true"} && !halted
                #{@filter} do
                  yield self
                end
              else
                yield self
              end
            end
          RUBY_EVAL
          "#{name}(halted) do"
        end
      end

      # This will supply contents for around and after filters, but not
      # before filters (for the backward pass).
      def end(key=nil, object=nil)
        return if key && !object.send("_one_time_conditions_valid_#{@callback_id}?")

        case @kind
        when :after
          # if condition    # after_save :filter_name, :if => :condition
          #   filter_name
          # end
          [@compiled_options[0], @filter, @compiled_options[1]].compact.join("\n")
        when :around
          <<-RUBY_EVAL
            value
          end
          RUBY_EVAL
        end
      end

      private

      # Options support the same options as filters themselves (and support
      # symbols, string, procs, and objects), so compile a conditional
      # expression based on the options
      def _compile_options(options)
        return [] if options[:if].empty? && options[:unless].empty?

        conditions = []

        unless options[:if].empty?
          conditions << Array.wrap(_compile_filter(options[:if]))
        end

        unless options[:unless].empty?
          conditions << Array.wrap(_compile_filter(options[:unless])).map {|f| "!#{f}"}
        end

        ["if #{conditions.flatten.join(" && ")}", "end"]
      end

      # Filters support:
      #
      #   Arrays::  Used in conditions. This is used to specify
      #             multiple conditions. Used internally to
      #             merge conditions from skip_* filters
      #   Symbols:: A method to call
      #   Strings:: Some content to evaluate
      #   Procs::   A proc to call with the object
      #   Objects:: An object with a before_foo method on it to call
      #
      # All of these objects are compiled into methods and handled
      # the same after this point:
      #
      #   Arrays::  Merged together into a single filter
      #   Symbols:: Already methods
      #   Strings:: class_eval'ed into methods
      #   Procs::   define_method'ed into methods
      #   Objects::
      #     a method is created that calls the before_foo method
      #     on the object.
      #
      def _compile_filter(filter)
        method_name = "_callback_#{@kind}_#{next_id}"
        case filter
        when Array
          filter.map {|f| _compile_filter(f)}
        when Symbol
          filter
        when String
          "(#{filter})"
        when Proc
          @klass.send(:define_method, method_name, &filter)
          return method_name if filter.arity <= 0

          method_name << (filter.arity == 1 ? "(self)" : " self, Proc.new ")
        else
          @klass.send(:define_method, "#{method_name}_object") { filter }

          _normalize_legacy_filter(kind, filter)
          scopes = Array.wrap(chain.config[:scope])
          method_to_call = scopes.map{ |s| s.is_a?(Symbol) ? send(s) : s }.join("_")

          @klass.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def #{method_name}(&blk)
              #{method_name}_object.send(:#{method_to_call}, self, &blk)
            end
          RUBY_EVAL

          method_name
        end
      end

      def _normalize_legacy_filter(kind, filter)
        if !filter.respond_to?(kind) && filter.respond_to?(:filter)
          filter.singleton_class.class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def #{kind}(context, &block) filter(context, &block) end
          RUBY_EVAL
        elsif filter.respond_to?(:before) && filter.respond_to?(:after) && kind == :around
          def filter.around(context)
            should_continue = before(context)
            yield if should_continue
            after(context)
          end
        end
      end
    end

    # An Array with a compile method
    class CallbackChain < Array #:nodoc:#
      attr_reader :name, :config

      def initialize(name, config)
        @name = name
        @config = {
          :terminator => "false",
          :rescuable => false,
          :scope => [ :kind ]
        }.merge(config)
      end

      def compile(key=nil, object=nil)
        method = []
        method << "value = nil"
        method << "halted = false"

        each do |callback|
          method << callback.start(key, object)
        end

        if config[:rescuable]
          method << "rescued_error = nil"
          method << "begin"
        end

        method << "value = yield if block_given? && !halted"

        if config[:rescuable]
          method << "rescue Exception => e"
          method << "rescued_error = e"
          method << "end"
        end

        reverse_each do |callback|
          method << callback.end(key, object)
        end

        method << "raise rescued_error if rescued_error" if config[:rescuable]
        method << "halted ? false : (block_given? ? value : true)"
        method.compact.join("\n")
      end
    end

    module ClassMethods
      # Generate the internal runner method called by +run_callbacks+.
      def __define_runner(symbol) #:nodoc:
        body = send("_#{symbol}_callbacks").compile

        silence_warnings do
          undef_method "_run_#{symbol}_callbacks" if method_defined?("_run_#{symbol}_callbacks")
          class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def _run_#{symbol}_callbacks(key = nil, &blk)
              if key
                name = "_run__\#{self.class.name.hash.abs}__#{symbol}__\#{key.hash.abs}__callbacks"

                unless respond_to?(name)
                  self.class.__create_keyed_callback(name, :#{symbol}, self, &blk)
                end

                send(name, &blk)
              else
                #{body}
              end
            end
            private :_run_#{symbol}_callbacks
          RUBY_EVAL
        end
      end

      # This is called the first time a callback is called with a particular
      # key. It creates a new callback method for the key, calculating
      # which callbacks can be omitted because of per_key conditions.
      #
      def __create_keyed_callback(name, kind, object, &blk) #:nodoc:
        @_keyed_callbacks ||= {}
        @_keyed_callbacks[name] ||= begin
          str = send("_#{kind}_callbacks").compile(name, object)
          class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
            def #{name}() #{str} end
            protected :#{name}
          RUBY_EVAL
          true
        end
      end

      # This is used internally to append, prepend and skip callbacks to the
      # CallbackChain.
      #
      def __update_callbacks(name, filters = [], block = nil) #:nodoc:
        type = filters.first.in?([:before, :after, :around]) ? filters.shift : :before
        options = filters.last.is_a?(Hash) ? filters.pop : {}
        filters.unshift(block) if block

        ([self] + ActiveSupport::DescendantsTracker.descendants(self)).reverse.each do |target|
          chain = target.send("_#{name}_callbacks")
          yield target, chain.dup, type, filters, options
          target.__define_runner(name)
        end
      end

      # 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 <tt>:scope</tt> 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.
      #
      # ===== Options
      #
      # * <tt>:if</tt> - A symbol naming an instance method or a proc; the callback
      #   will be called only when it returns a true value.
      # * <tt>:unless</tt> - A symbol naming an instance method or a proc; the callback
      #   will be called only when it returns a false value.
      # * <tt>:prepend</tt> - If true, the callback will be prepended to the existing
      #   chain rather than appended.
      # * <tt>:per_key</tt> - A hash with <tt>:if</tt> and <tt>:unless</tt> options;
      #   see "Per-key conditions" below.
      #
      # ===== Per-key conditions
      #
      # 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.
      #
      def set_callback(name, *filter_list, &block)
        mapped = nil

        __update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
          mapped ||= filters.map do |filter|
            Callback.new(chain, filter, type, options.dup, self)
          end

          filters.each do |filter|
            chain.delete_if {|c| c.matches?(type, filter) }
          end

          options[:prepend] ? chain.unshift(*(mapped.reverse)) : chain.push(*mapped)

          target.send("_#{name}_callbacks=", chain)
        end
      end

      # Skip a previously set callback. Like +set_callback+, <tt>:if</tt> or <tt>:unless</tt>
      # 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
      #
      def skip_callback(name, *filter_list, &block)
        __update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
          filters.each do |filter|
            filter = chain.find {|c| c.matches?(type, filter) }

            if filter && options.any?
              new_filter = filter.clone(chain, self)
              chain.insert(chain.index(filter), new_filter)
              new_filter.recompile!(options, options[:per_key] || {})
            end

            chain.delete(filter)
          end
          target.send("_#{name}_callbacks=", chain)
        end
      end

      # Remove all set callbacks for the given event.
      #
      def reset_callbacks(symbol)
        callbacks = send("_#{symbol}_callbacks")

        ActiveSupport::DescendantsTracker.descendants(self).each do |target|
          chain = target.send("_#{symbol}_callbacks").dup
          callbacks.each { |c| chain.delete(c) }
          target.send("_#{symbol}_callbacks=", chain)
          target.__define_runner(symbol)
        end

        self.send("_#{symbol}_callbacks=", callbacks.dup.clear)

        __define_runner(symbol)
      end

      # Define sets of events in the object lifecycle that support callbacks.
      #
      #   define_callbacks :validate
      #   define_callbacks :initialize, :save, :destroy
      #
      # ===== Options
      #
      # * <tt>:terminator</tt> - Determines when a before filter will halt the callback
      #   chain, preventing following callbacks from being called and the event from being
      #   triggered. This is a string to be eval'ed. The result of the callback is available
      #   in the <tt>result</tt> variable.
      #
      #     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.
      #
      # * <tt>:rescuable</tt> - By default, after filters are not executed if
      #   the given block or a before filter raises an error. By setting this option
      #   to <tt>true</tt> exception raised by given block is stored and after
      #   executing all the after callbacks the stored exception is raised.
      #
      # * <tt>:scope</tt> - Indicates which methods should be executed when an object
      #   is used as a callback.
      #
      #     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 <tt>Audit#before</tt> will
      #   be called. On the other hand
      #
      #     define_callbacks :save, :scope => [:kind, :name]
      #
      #   would trigger <tt>Audit#before_save</tt> instead. That's constructed by calling
      #   <tt>#{kind}_#{name}</tt> 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 <tt>Audit#save</tt>.
      #
      def define_callbacks(*callbacks)
        config = callbacks.last.is_a?(Hash) ? callbacks.pop : {}
        callbacks.each do |callback|
          class_attribute "_#{callback}_callbacks"
          send("_#{callback}_callbacks=", CallbackChain.new(callback, config))
          __define_runner(callback)
        end
      end
    end
  end
end