aboutsummaryrefslogtreecommitdiffstats
path: root/actionpack/lib/action_view/helpers/form_helper.rb
blob: 305d6b312881d5d08075b157a2b7475240308600 (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
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
require 'cgi'
require 'action_view/helpers/date_helper'
require 'action_view/helpers/tag_helper'
require 'action_view/helpers/form_tag_helper'
require 'active_support/core_ext/class/inheritable_attributes'
require 'active_support/core_ext/hash/slice'

module ActionView
  module Helpers
    # Form helpers are designed to make working with models much easier
    # compared to using just standard HTML elements by providing a set of
    # methods for creating forms based on your models. This helper generates
    # the HTML for forms, providing a method for each sort of input
    # (e.g., text, password, select, and so on). When the form is submitted
    # (i.e., when the user hits the submit button or <tt>form.submit</tt> is
    # called via JavaScript), the form inputs will be bundled into the
    # <tt>params</tt> object and passed back to the controller.
    #
    # There are two types of form helpers: those that specifically work with
    # model attributes and those that don't. This helper deals with those that
    # work with model attributes; to see an example of form helpers that don't
    # work with model attributes, check the ActionView::Helpers::FormTagHelper
    # documentation.
    #
    # The core method of this helper, form_for, gives you the ability to create
    # a form for a model instance; for example, let's say that you have a model
    # <tt>Person</tt> and want to create a new instance of it:
    #
    #     # Note: a @person variable will have been created in the controller.
    #     # For example: @person = Person.new
    #     <% form_for :person, @person, :url => { :action => "create" } do |f| %>
    #       <%= f.text_field :first_name %>
    #       <%= f.text_field :last_name %>
    #       <%= submit_tag 'Create' %>
    #     <% end %>
    #
    # The HTML generated for this would be:
    #
    #     <form action="/persons/create" method="post">
    #       <input id="person_first_name" name="person[first_name]" size="30" type="text" />
    #       <input id="person_last_name" name="person[last_name]" size="30" type="text" />
    #       <input name="commit" type="submit" value="Create" />
    #     </form>
    #
    # If you are using a partial for your form fields, you can use this shortcut:
    #
    #     <% form_for :person, @person, :url => { :action => "create" } do |f| %>
    #       <%= render :partial => f %>
    #       <%= submit_tag 'Create' %>
    #     <% end %>
    #
    # This example will render the <tt>people/_form</tt> partial, setting a
    # local variable called <tt>form</tt> which references the yielded
    # FormBuilder. The <tt>params</tt> object created when this form is
    # submitted would look like:
    #
    #     {"action"=>"create", "controller"=>"persons", "person"=>{"first_name"=>"William", "last_name"=>"Smith"}}
    #
    # The params hash has a nested <tt>person</tt> value, which can therefore
    # be accessed with <tt>params[:person]</tt> in the controller. If were
    # editing/updating an instance (e.g., <tt>Person.find(1)</tt> rather than
    # <tt>Person.new</tt> in the controller), the objects attribute values are
    # filled into the form (e.g., the <tt>person_first_name</tt> field would
    # have that person's first name in it).
    #
    # If the object name contains square brackets the id for the object will be
    # inserted. For example:
    #
    #   <%= text_field "person[]", "name" %>
    #
    # ...will generate the following ERb.
    #
    #   <input type="text" id="person_<%= @person.id %>_name" name="person[<%= @person.id %>][name]" value="<%= @person.name %>" />
    #
    # If the helper is being used to generate a repetitive sequence of similar
    # form elements, for example in a partial used by
    # <tt>render_collection_of_partials</tt>, the <tt>index</tt> option may
    # come in handy. Example:
    #
    #   <%= text_field "person", "name", "index" => 1 %>
    #
    # ...becomes...
    #
    #   <input type="text" id="person_1_name" name="person[1][name]" value="<%= @person.name %>" />
    #
    # An <tt>index</tt> option may also be passed to <tt>form_for</tt> and
    # <tt>fields_for</tt>.  This automatically applies the <tt>index</tt> to
    # all the nested fields.
    #
    # There are also methods for helping to build form tags in
    # link:classes/ActionView/Helpers/FormOptionsHelper.html,
    # link:classes/ActionView/Helpers/DateHelper.html, and
    # link:classes/ActionView/Helpers/ActiveRecordHelper.html
    module FormHelper
      # Creates a form and a scope around a specific model object that is used
      # as a base for questioning about values for the fields.
      #
      # Rails provides succinct resource-oriented form generation with +form_for+
      # like this:
      #
      #   <% form_for @offer do |f| %>
      #     <%= f.label :version, 'Version' %>:
      #     <%= f.text_field :version %><br />
      #     <%= f.label :author, 'Author' %>:
      #     <%= f.text_field :author %><br />
      #   <% end %>
      #
      # There, +form_for+ is able to generate the rest of RESTful form
      # parameters based on introspection on the record, but to understand what
      # it does we need to dig first into the alternative generic usage it is
      # based upon.
      #
      # === Generic form_for
      #
      # The generic way to call +form_for+ yields a form builder around a
      # model:
      #
      #   <% form_for :person, :url => { :action => "update" } do |f| %>
      #     <%= f.error_messages %>
      #     First name: <%= f.text_field :first_name %><br />
      #     Last name : <%= f.text_field :last_name %><br />
      #     Biography : <%= f.text_area :biography %><br />
      #     Admin?    : <%= f.check_box :admin %><br />
      #   <% end %>
      #
      # There, the first argument is a symbol or string with the name of the
      # object the form is about, and also the name of the instance variable
      # the object is stored in.
      #
      # The form builder acts as a regular form helper that somehow carries the
      # model. Thus, the idea is that
      #
      #   <%= f.text_field :first_name %>
      #
      # gets expanded to
      #
      #   <%= text_field :person, :first_name %>
      #
      # If the instance variable is not <tt>@person</tt> you can pass the actual
      # record as the second argument:
      #
      #   <% form_for :person, person, :url => { :action => "update" } do |f| %>
      #     ...
      #   <% end %>
      #
      # In that case you can think
      #
      #   <%= f.text_field :first_name %>
      #
      # gets expanded to
      #
      #   <%= text_field :person, :first_name, :object => person %>
      #
      # You can even display error messages of the wrapped model this way:
      #
      #   <%= f.error_messages %>
      #
      # In any of its variants, the rightmost argument to +form_for+ is an
      # optional hash of options:
      #
      # * <tt>:url</tt> - The URL the form is submitted to. It takes the same
      #   fields you pass to +url_for+ or +link_to+. In particular you may pass
      #   here a named route directly as well. Defaults to the current action.
      # * <tt>:html</tt> - Optional HTML attributes for the form tag.
      #
      # Worth noting is that the +form_for+ tag is called in a ERb evaluation
      # block, not an ERb output block. So that's <tt><% %></tt>, not
      # <tt><%= %></tt>.
      #
      # Also note that +form_for+ doesn't create an exclusive scope. It's still
      # possible to use both the stand-alone FormHelper methods and methods
      # from FormTagHelper. For example:
      #
      #   <% form_for :person, @person, :url => { :action => "update" } do |f| %>
      #     First name: <%= f.text_field :first_name %>
      #     Last name : <%= f.text_field :last_name %>
      #     Biography : <%= text_area :person, :biography %>
      #     Admin?    : <%= check_box_tag "person[admin]", @person.company.admin? %>
      #   <% end %>
      #
      # This also works for the methods in FormOptionHelper and DateHelper that
      # are designed to work with an object as base, like
      # FormOptionHelper#collection_select and DateHelper#datetime_select.
      #
      # === Resource-oriented style
      #
      # As we said above, in addition to manually configuring the +form_for+
      # call, you can rely on automated resource identification, which will use
      # the conventions and named routes of that approach. This is the
      # preferred way to use +form_for+ nowadays.
      #
      # For example, if <tt>@post</tt> is an existing record you want to edit
      #
      #   <% form_for @post do |f| %>
      #     ...
      #   <% end %>
      #
      # is equivalent to something like:
      #
      #   <% form_for :post, @post, :url => post_path(@post), :html => { :method => :put, :class => "edit_post", :id => "edit_post_45" } do |f| %>
      #     ...
      #   <% end %>
      #
      # And for new records
      #
      #   <% form_for(Post.new) do |f| %>
      #     ...
      #   <% end %>
      #
      # expands to
      #
      #   <% form_for :post, Post.new, :url => posts_path, :html => { :class => "new_post", :id => "new_post" } do |f| %>
      #     ...
      #   <% end %>
      #
      # You can also overwrite the individual conventions, like this:
      #
      #   <% form_for(@post, :url => super_post_path(@post)) do |f| %>
      #     ...
      #   <% end %>
      #
      # And for namespaced routes, like +admin_post_url+:
      #
      #   <% form_for([:admin, @post]) do |f| %>
      #    ...
      #   <% end %>
      #
      # === Unobtrusive JavaScript
      # 
      # Specifying:  
      #  
      #    :remote => true
      #
      # in the options hash creates a form that will allow the unobtrusive JavaScript drivers to modify its
      # behaviour. The expected default behaviour is an XMLHttpRequest in the background instead of the regular 
      # POST arrangement, but ultimately the behaviour is the choice of the JavaScript driver implementor.
      # Even though it's using JavaScript to serialize the form elements, the form submission will work just like 
      # a regular submission as viewed by the receiving side (all elements available in <tt>params</tt>).
      #
      # Example:
      #
      #   <% form_for(:post, @post, :remote => true, :html => { :id => 'create-post', :method => :put }) do |f| %>
      #     ...
      #   <% end %>
      #
      # The HTML generated for this would be:
      #
      #   <form action='http://www.example.com' id='create-post' method='post' data-remote='true'>
      #     <div style='margin:0;padding:0;display:inline'>
      #       <input name='_method' type='hidden' value='put' />
      #     </div>
      #     ...
      #   </form>
      #
      # === Customized form builders
      #
      # You can also build forms using a customized FormBuilder class. Subclass
      # FormBuilder and override or define some more helpers, then use your
      # custom builder. For example, let's say you made a helper to
      # automatically add labels to form inputs.
      #
      #   <% form_for :person, @person, :url => { :action => "update" }, :builder => LabellingFormBuilder do |f| %>
      #     <%= f.text_field :first_name %>
      #     <%= f.text_field :last_name %>
      #     <%= text_area :person, :biography %>
      #     <%= check_box_tag "person[admin]", @person.company.admin? %>
      #   <% end %>
      #
      # In this case, if you use this:
      #
      #   <%= render :partial => f %>
      #
      # The rendered template is <tt>people/_labelling_form</tt> and the local
      # variable referencing the form builder is called
      # <tt>labelling_form</tt>.
      #
      # The custom FormBuilder class is automatically merged with the options
      # of a nested fields_for call, unless it's explicitely set.
      #
      # In many cases you will want to wrap the above in another helper, so you
      # could do something like the following:
      #
      #   def labelled_form_for(record_or_name_or_array, *args, &proc)
      #     options = args.extract_options!
      #     form_for(record_or_name_or_array, *(args << options.merge(:builder => LabellingFormBuilder)), &proc)
      #   end
      #
      # If you don't need to attach a form to a model instance, then check out
      # FormTagHelper#form_tag.
      def form_for(record_or_name_or_array, *args, &proc)
        raise ArgumentError, "Missing block" unless block_given?

        options = args.extract_options!

        case record_or_name_or_array
        when String, Symbol
          object_name = record_or_name_or_array
        when Array
          object = record_or_name_or_array.last
          object_name = ActionController::RecordIdentifier.singular_class_name(object)
          apply_form_for_options!(record_or_name_or_array, options)
          args.unshift object
        else
          object = record_or_name_or_array
          object_name = ActionController::RecordIdentifier.singular_class_name(object)
          apply_form_for_options!([object], options)
          args.unshift object
        end

        options[:html][:remote] = true if options.delete(:remote)

        safe_concat(form_tag(options.delete(:url) || {}, options.delete(:html) || {}))
        fields_for(object_name, *(args << options), &proc)
        safe_concat('</form>')
      end

      def apply_form_for_options!(object_or_array, options) #:nodoc:
        object = object_or_array.is_a?(Array) ? object_or_array.last : object_or_array

        object = convert_to_model(object)

        html_options =
          if object.respond_to?(:new_record?) && object.new_record?
            { :class  => dom_class(object, :new),  :id => dom_id(object), :method => :post }
          else
            { :class  => dom_class(object, :edit), :id => dom_id(object, :edit), :method => :put }
          end

        options[:html] ||= {}
        options[:html].reverse_merge!(html_options)
        options[:url] ||= polymorphic_path(object_or_array)
      end

      # Creates a scope around a specific model object like form_for, but
      # doesn't create the form tags themselves. This makes fields_for suitable
      # for specifying additional model objects in the same form.
      #
      # === Generic Examples
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     First name: <%= person_form.text_field :first_name %>
      #     Last name : <%= person_form.text_field :last_name %>
      #
      #     <% fields_for @person.permission do |permission_fields| %>
      #       Admin?  : <%= permission_fields.check_box :admin %>
      #     <% end %>
      #   <% end %>
      #
      # ...or if you have an object that needs to be represented as a different
      # parameter, like a Client that acts as a Person:
      #
      #   <% fields_for :person, @client do |permission_fields| %>
      #     Admin?: <%= permission_fields.check_box :admin %>
      #   <% end %>
      #
      # ...or if you don't have an object, just a name of the parameter:
      #
      #   <% fields_for :person do |permission_fields| %>
      #     Admin?: <%= permission_fields.check_box :admin %>
      #   <% end %>
      #
      # Note: This also works for the methods in FormOptionHelper and
      # DateHelper that are designed to work with an object as base, like
      # FormOptionHelper#collection_select and DateHelper#datetime_select.
      #
      # === Nested Attributes Examples
      #
      # When the object belonging to the current scope has a nested attribute
      # writer for a certain attribute, fields_for will yield a new scope
      # for that attribute. This allows you to create forms that set or change
      # the attributes of a parent object and its associations in one go.
      #
      # Nested attribute writers are normal setter methods named after an
      # association. The most common way of defining these writers is either
      # with +accepts_nested_attributes_for+ in a model definition or by
      # defining a method with the proper name. For example: the attribute
      # writer for the association <tt>:address</tt> is called
      # <tt>address_attributes=</tt>.
      #
      # Whether a one-to-one or one-to-many style form builder will be yielded
      # depends on whether the normal reader method returns a _single_ object
      # or an _array_ of objects.
      #
      # ==== One-to-one
      #
      # Consider a Person class which returns a _single_ Address from the
      # <tt>address</tt> reader method and responds to the
      # <tt>address_attributes=</tt> writer method:
      #
      #   class Person
      #     def address
      #       @address
      #     end
      #
      #     def address_attributes=(attributes)
      #       # Process the attributes hash
      #     end
      #   end
      #
      # This model can now be used with a nested fields_for, like so:
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     ...
      #     <% person_form.fields_for :address do |address_fields| %>
      #       Street  : <%= address_fields.text_field :street %>
      #       Zip code: <%= address_fields.text_field :zip_code %>
      #     <% end %>
      #   <% end %>
      #
      # When address is already an association on a Person you can use
      # +accepts_nested_attributes_for+ to define the writer method for you:
      #
      #   class Person < ActiveRecord::Base
      #     has_one :address
      #     accepts_nested_attributes_for :address
      #   end
      #
      # If you want to destroy the associated model through the form, you have
      # to enable it first using the <tt>:allow_destroy</tt> option for
      # +accepts_nested_attributes_for+:
      #
      #   class Person < ActiveRecord::Base
      #     has_one :address
      #     accepts_nested_attributes_for :address, :allow_destroy => true
      #   end
      #
      # Now, when you use a form element with the <tt>_destroy</tt> parameter,
      # with a value that evaluates to +true+, you will destroy the associated
      # model (eg. 1, '1', true, or 'true'):
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     ...
      #     <% person_form.fields_for :address do |address_fields| %>
      #       ...
      #       Delete: <%= address_fields.check_box :_destroy %>
      #     <% end %>
      #   <% end %>
      #
      # ==== One-to-many
      #
      # Consider a Person class which returns an _array_ of Project instances
      # from the <tt>projects</tt> reader method and responds to the
      # <tt>projects_attributes=</tt> writer method:
      #
      #   class Person
      #     def projects
      #       [@project1, @project2]
      #     end
      #
      #     def projects_attributes=(attributes)
      #       # Process the attributes hash
      #     end
      #   end
      #
      # This model can now be used with a nested fields_for. The block given to
      # the nested fields_for call will be repeated for each instance in the
      # collection:
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     ...
      #     <% person_form.fields_for :projects do |project_fields| %>
      #       <% if project_fields.object.active? %>
      #         Name: <%= project_fields.text_field :name %>
      #       <% end %>
      #     <% end %>
      #   <% end %>
      #
      # It's also possible to specify the instance to be used:
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     ...
      #     <% @person.projects.each do |project| %>
      #       <% if project.active? %>
      #         <% person_form.fields_for :projects, project do |project_fields| %>
      #           Name: <%= project_fields.text_field :name %>
      #         <% end %>
      #       <% end %>
      #     <% end %>
      #   <% end %>
      #
      # Or a collection to be used:
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     ...
      #     <% person_form.fields_for :projects, @active_projects do |project_fields| %>
      #       Name: <%= project_fields.text_field :name %>
      #     <% end %>
      #   <% end %>
      #
      # When projects is already an association on Person you can use
      # +accepts_nested_attributes_for+ to define the writer method for you:
      #
      #   class Person < ActiveRecord::Base
      #     has_many :projects
      #     accepts_nested_attributes_for :projects
      #   end
      #
      # If you want to destroy any of the associated models through the
      # form, you have to enable it first using the <tt>:allow_destroy</tt>
      # option for +accepts_nested_attributes_for+:
      #
      #   class Person < ActiveRecord::Base
      #     has_many :projects
      #     accepts_nested_attributes_for :projects, :allow_destroy => true
      #   end
      #
      # This will allow you to specify which models to destroy in the
      # attributes hash by adding a form element for the <tt>_destroy</tt>
      # parameter with a value that evaluates to +true+
      # (eg. 1, '1', true, or 'true'):
      #
      #   <% form_for @person, :url => { :action => "update" } do |person_form| %>
      #     ...
      #     <% person_form.fields_for :projects do |project_fields| %>
      #       Delete: <%= project_fields.check_box :_destroy %>
      #     <% end %>
      #   <% end %>
      def fields_for(record_or_name_or_array, *args, &block)
        raise ArgumentError, "Missing block" unless block_given?
        options = args.extract_options!

        case record_or_name_or_array
        when String, Symbol
          object_name = record_or_name_or_array
          object = args.first
        else
          object = record_or_name_or_array
          object_name = ActionController::RecordIdentifier.singular_class_name(object)
        end

        builder = options[:builder] || ActionView::Base.default_form_builder
        yield builder.new(object_name, object, self, options, block)
      end

      # Returns a label tag tailored for labelling an input field for a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). The text of label will default to the attribute name unless a translation
      # is found in the current I18n locale (through helpers.label.<modelname>.<attribute>) or you specify it explicitly.
      # Additional options on the label tag can be passed as a hash with +options+. These options will be tagged
      # onto the HTML as an HTML element attribute as in the example shown, except for the <tt>:value</tt> option, which is designed to
      # target labels for radio_button tags (where the value is used in the ID of the input tag).
      #
      # ==== Examples
      #   label(:post, :title)
      #   # => <label for="post_title">Title</label>
      #
      #   You can localize your labels based on model and attribute names.
      #   For example you can define the following in your locale (e.g. en.yml)
      #
      #   helpers:
      #     label:
      #       post:
      #         body: "Write your entire text here"
      #
      #   Which then will result in
      #
      #   label(:post, :body)
      #   # => <label for="post_body">Write your entire text here</label>
      #
      #   Localization can also be based purely on the translation of the attribute-name like this:
      #
      #   activemodel:
      #     attribute:
      #       post:
      #         cost: "Total cost"
      #
      #   label(:post, :cost)
      #   # => <label for="post_cost">Total cost</label>
      #
      #   label(:post, :title, "A short title")
      #   # => <label for="post_title">A short title</label>
      #
      #   label(:post, :title, "A short title", :class => "title_label")
      #   # => <label for="post_title" class="title_label">A short title</label>
      #
      #   label(:post, :privacy, "Public Post", :value => "public")
      #   # => <label for="post_privacy_public">Public Post</label>
      #
      def label(object_name, method, text = nil, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_label_tag(text, options)
      end

      # Returns an input tag of the "text" type tailored for accessing a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). Additional options on the input tag can be passed as a
      # hash with +options+. These options will be tagged onto the HTML as an HTML element attribute as in the example
      # shown.
      #
      # ==== Examples
      #   text_field(:post, :title, :size => 20)
      #   # => <input type="text" id="post_title" name="post[title]" size="20" value="#{@post.title}" />
      #
      #   text_field(:post, :title, :class => "create_input")
      #   # => <input type="text" id="post_title" name="post[title]" value="#{@post.title}" class="create_input" />
      #
      #   text_field(:session, :user, :onchange => "if $('session[user]').value == 'admin' { alert('Your login can not be admin!'); }")
      #   # => <input type="text" id="session_user" name="session[user]" value="#{@session.user}" onchange = "if $('session[user]').value == 'admin' { alert('Your login can not be admin!'); }"/>
      #
      #   text_field(:snippet, :code, :size => 20, :class => 'code_input')
      #   # => <input type="text" id="snippet_code" name="snippet[code]" size="20" value="#{@snippet.code}" class="code_input" />
      #
      def text_field(object_name, method, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("text", options)
      end

      # Returns an input tag of the "password" type tailored for accessing a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). Additional options on the input tag can be passed as a
      # hash with +options+. These options will be tagged onto the HTML as an HTML element attribute as in the example
      # shown.
      #
      # ==== Examples
      #   password_field(:login, :pass, :size => 20)
      #   # => <input type="text" id="login_pass" name="login[pass]" size="20" value="#{@login.pass}" />
      #
      #   password_field(:account, :secret, :class => "form_input")
      #   # => <input type="text" id="account_secret" name="account[secret]" value="#{@account.secret}" class="form_input" />
      #
      #   password_field(:user, :password, :onchange => "if $('user[password]').length > 30 { alert('Your password needs to be shorter!'); }")
      #   # => <input type="text" id="user_password" name="user[password]" value="#{@user.password}" onchange = "if $('user[password]').length > 30 { alert('Your password needs to be shorter!'); }"/>
      #
      #   password_field(:account, :pin, :size => 20, :class => 'form_input')
      #   # => <input type="text" id="account_pin" name="account[pin]" size="20" value="#{@account.pin}" class="form_input" />
      #
      def password_field(object_name, method, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("password", options)
      end

      # Returns a hidden input tag tailored for accessing a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). Additional options on the input tag can be passed as a
      # hash with +options+. These options will be tagged onto the HTML as an HTML element attribute as in the example
      # shown.
      #
      # ==== Examples
      #   hidden_field(:signup, :pass_confirm)
      #   # => <input type="hidden" id="signup_pass_confirm" name="signup[pass_confirm]" value="#{@signup.pass_confirm}" />
      #
      #   hidden_field(:post, :tag_list)
      #   # => <input type="hidden" id="post_tag_list" name="post[tag_list]" value="#{@post.tag_list}" />
      #
      #   hidden_field(:user, :token)
      #   # => <input type="hidden" id="user_token" name="user[token]" value="#{@user.token}" />
      def hidden_field(object_name, method, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("hidden", options)
      end

      # Returns an file upload input tag tailored for accessing a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). Additional options on the input tag can be passed as a
      # hash with +options+. These options will be tagged onto the HTML as an HTML element attribute as in the example
      # shown.
      #
      # ==== Examples
      #   file_field(:user, :avatar)
      #   # => <input type="file" id="user_avatar" name="user[avatar]" />
      #
      #   file_field(:post, :attached, :accept => 'text/html')
      #   # => <input type="file" id="post_attached" name="post[attached]" />
      #
      #   file_field(:attachment, :file, :class => 'file_input')
      #   # => <input type="file" id="attachment_file" name="attachment[file]" class="file_input" />
      #
      def file_field(object_name, method, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_input_field_tag("file", options)
      end

      # Returns a textarea opening and closing tag set tailored for accessing a specified attribute (identified by +method+)
      # on an object assigned to the template (identified by +object+). Additional options on the input tag can be passed as a
      # hash with +options+.
      #
      # ==== Examples
      #   text_area(:post, :body, :cols => 20, :rows => 40)
      #   # => <textarea cols="20" rows="40" id="post_body" name="post[body]">
      #   #      #{@post.body}
      #   #    </textarea>
      #
      #   text_area(:comment, :text, :size => "20x30")
      #   # => <textarea cols="20" rows="30" id="comment_text" name="comment[text]">
      #   #      #{@comment.text}
      #   #    </textarea>
      #
      #   text_area(:application, :notes, :cols => 40, :rows => 15, :class => 'app_input')
      #   # => <textarea cols="40" rows="15" id="application_notes" name="application[notes]" class="app_input">
      #   #      #{@application.notes}
      #   #    </textarea>
      #
      #   text_area(:entry, :body, :size => "20x20", :disabled => 'disabled')
      #   # => <textarea cols="20" rows="20" id="entry_body" name="entry[body]" disabled="disabled">
      #   #      #{@entry.body}
      #   #    </textarea>
      def text_area(object_name, method, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_text_area_tag(options)
      end

      # Returns a checkbox tag tailored for accessing a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). This object must be an instance object (@object) and not a local object.
      # It's intended that +method+ returns an integer and if that integer is above zero, then the checkbox is checked.
      # Additional options on the input tag can be passed as a hash with +options+. The +checked_value+ defaults to 1
      # while the default +unchecked_value+ is set to 0 which is convenient for boolean values.
      #
      # ==== Gotcha
      #
      # The HTML specification says unchecked check boxes are not successful, and
      # thus web browsers do not send them. Unfortunately this introduces a gotcha:
      # if an +Invoice+ model has a +paid+ flag, and in the form that edits a paid
      # invoice the user unchecks its check box, no +paid+ parameter is sent. So,
      # any mass-assignment idiom like
      #
      #   @invoice.update_attributes(params[:invoice])
      #
      # wouldn't update the flag.
      #
      # To prevent this the helper generates an auxiliary hidden field before
      # the very check box. The hidden field has the same name and its
      # attributes mimick an unchecked check box.
      #
      # This way, the client either sends only the hidden field (representing
      # the check box is unchecked), or both fields. Since the HTML specification
      # says key/value pairs have to be sent in the same order they appear in the
      # form, and parameters extraction gets the last occurrence of any repeated
      # key in the query string, that works for ordinary forms.
      #
      # Unfortunately that workaround does not work when the check box goes
      # within an array-like parameter, as in
      #
      #   <% fields_for "project[invoice_attributes][]", invoice, :index => nil do |form| %>
      #     <%= form.check_box :paid %>
      #     ...
      #   <% end %>
      #
      # because parameter name repetition is precisely what Rails seeks to distinguish
      # the elements of the array. For each item with a checked check box you
      # get an extra ghost item with only that attribute, assigned to "0".
      #
      # In that case it is preferable to either use +check_box_tag+ or to use
      # hashes instead of arrays.
      #
      # ==== Examples
      #   # Let's say that @post.validated? is 1:
      #   check_box("post", "validated")
      #   # => <input name="post[validated]" type="hidden" value="0" />
      #   #    <input type="checkbox" id="post_validated" name="post[validated]" value="1" />
      #
      #   # Let's say that @puppy.gooddog is "no":
      #   check_box("puppy", "gooddog", {}, "yes", "no")
      #   # => <input name="puppy[gooddog]" type="hidden" value="no" />
      #   #    <input type="checkbox" id="puppy_gooddog" name="puppy[gooddog]" value="yes" />
      #
      #   check_box("eula", "accepted", { :class => 'eula_check' }, "yes", "no")
      #   # => <input name="eula[accepted]" type="hidden" value="no" />
      #   #    <input type="checkbox" class="eula_check" id="eula_accepted" name="eula[accepted]" value="yes" />
      #
      def check_box(object_name, method, options = {}, checked_value = "1", unchecked_value = "0")
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_check_box_tag(options, checked_value, unchecked_value)
      end

      # Returns a radio button tag for accessing a specified attribute (identified by +method+) on an object
      # assigned to the template (identified by +object+). If the current value of +method+ is +tag_value+ the
      # radio button will be checked.
      #
      # To force the radio button to be checked pass <tt>:checked => true</tt> in the
      # +options+ hash. You may pass HTML options there as well.
      #
      # ==== Examples
      #   # Let's say that @post.category returns "rails":
      #   radio_button("post", "category", "rails")
      #   radio_button("post", "category", "java")
      #   # => <input type="radio" id="post_category_rails" name="post[category]" value="rails" checked="checked" />
      #   #    <input type="radio" id="post_category_java" name="post[category]" value="java" />
      #
      #   radio_button("user", "receive_newsletter", "yes")
      #   radio_button("user", "receive_newsletter", "no")
      #   # => <input type="radio" id="user_receive_newsletter_yes" name="user[receive_newsletter]" value="yes" />
      #   #    <input type="radio" id="user_receive_newsletter_no" name="user[receive_newsletter]" value="no" checked="checked" />
      def radio_button(object_name, method, tag_value, options = {})
        InstanceTag.new(object_name, method, self, options.delete(:object)).to_radio_button_tag(tag_value, options)
      end
    end

    module InstanceTagMethods #:nodoc:
      extend ActiveSupport::Concern
      include Helpers::TagHelper, Helpers::FormTagHelper

      attr_reader :method_name, :object_name

      DEFAULT_FIELD_OPTIONS     = { "size" => 30 }.freeze unless const_defined?(:DEFAULT_FIELD_OPTIONS)
      DEFAULT_RADIO_OPTIONS     = { }.freeze unless const_defined?(:DEFAULT_RADIO_OPTIONS)
      DEFAULT_TEXT_AREA_OPTIONS = { "cols" => 40, "rows" => 20 }.freeze unless const_defined?(:DEFAULT_TEXT_AREA_OPTIONS)

      def initialize(object_name, method_name, template_object, object = nil)
        @object_name, @method_name = object_name.to_s.dup, method_name.to_s.dup
        @template_object = template_object
        @object = object
        if @object_name.sub!(/\[\]$/,"") || @object_name.sub!(/\[\]\]$/,"]")
          if (object ||= @template_object.instance_variable_get("@#{Regexp.last_match.pre_match}")) && object.respond_to?(:to_param)
            @auto_index = object.to_param
          else
            raise ArgumentError, "object[] naming but object param and @object var don't exist or don't respond to to_param: #{object.inspect}"
          end
        end
      end

      def to_label_tag(text = nil, options = {})
        options = options.stringify_keys
        tag_value = options.delete("value")
        name_and_id = options.dup
        name_and_id["id"] = name_and_id["for"]
        add_default_name_and_id_for_value(tag_value, name_and_id)
        options.delete("index")
        options["for"] ||= name_and_id["id"]

        content = if text.blank?
          I18n.t("helpers.label.#{object_name}.#{method_name}", :default => "").presence
        else
          text.to_s
        end

        content ||= if object && object.class.respond_to?(:human_attribute_name)
          object.class.human_attribute_name(method_name)
        end

        content ||= method_name.humanize

        label_tag(name_and_id["id"], content, options)
      end

      def to_input_field_tag(field_type, options = {})
        options = options.stringify_keys
        options["size"] = options["maxlength"] || DEFAULT_FIELD_OPTIONS["size"] unless options.key?("size")
        options = DEFAULT_FIELD_OPTIONS.merge(options)
        if field_type == "hidden"
          options.delete("size")
        end
        options["type"]  ||= field_type
        options["value"] ||= value_before_type_cast(object) unless field_type == "file"
        options["value"] &&= html_escape(options["value"])
        add_default_name_and_id(options)
        tag("input", options)
      end

      def to_radio_button_tag(tag_value, options = {})
        options = DEFAULT_RADIO_OPTIONS.merge(options.stringify_keys)
        options["type"]     = "radio"
        options["value"]    = tag_value
        if options.has_key?("checked")
          cv = options.delete "checked"
          checked = cv == true || cv == "checked"
        else
          checked = self.class.radio_button_checked?(value(object), tag_value)
        end
        options["checked"]  = "checked" if checked
        add_default_name_and_id_for_value(tag_value, options)
        tag("input", options)
      end

      def to_text_area_tag(options = {})
        options = DEFAULT_TEXT_AREA_OPTIONS.merge(options.stringify_keys)
        add_default_name_and_id(options)

        if size = options.delete("size")
          options["cols"], options["rows"] = size.split("x") if size.respond_to?(:split)
        end

        content_tag("textarea", html_escape(options.delete('value') || value_before_type_cast(object)), options)
      end

      def to_check_box_tag(options = {}, checked_value = "1", unchecked_value = "0")
        options = options.stringify_keys
        options["type"]     = "checkbox"
        options["value"]    = checked_value
        if options.has_key?("checked")
          cv = options.delete "checked"
          checked = cv == true || cv == "checked"
        else
          checked = self.class.check_box_checked?(value(object), checked_value)
        end
        options["checked"] = "checked" if checked
        if options["multiple"]
          add_default_name_and_id_for_value(checked_value, options)
          options.delete("multiple")
        else
          add_default_name_and_id(options)
        end
        hidden = tag("input", "name" => options["name"], "type" => "hidden", "value" => options['disabled'] && checked ? checked_value : unchecked_value)
        checkbox = tag("input", options)
        (hidden + checkbox).html_safe
      end

      def to_boolean_select_tag(options = {})
        options = options.stringify_keys
        add_default_name_and_id(options)
        value = value(object)
        tag_text = "<select"
        tag_text << tag_options(options)
        tag_text << "><option value=\"false\""
        tag_text << " selected" if value == false
        tag_text << ">False</option><option value=\"true\""
        tag_text << " selected" if value
        tag_text << ">True</option></select>"
      end

      def to_content_tag(tag_name, options = {})
        content_tag(tag_name, value(object), options)
      end

      def object
        @object || @template_object.instance_variable_get("@#{@object_name}")
      rescue NameError
        # As @object_name may contain the nested syntax (item[subobject]) we
        # need to fallback to nil.
        nil
      end

      def value(object)
        self.class.value(object, @method_name)
      end

      def value_before_type_cast(object)
        self.class.value_before_type_cast(object, @method_name)
      end

      module ClassMethods
        def value(object, method_name)
          object.send method_name unless object.nil?
        end

        def value_before_type_cast(object, method_name)
          unless object.nil?
            object.respond_to?(method_name + "_before_type_cast") ?
            object.send(method_name + "_before_type_cast") :
            object.send(method_name)
          end
        end

        def check_box_checked?(value, checked_value)
          case value
          when TrueClass, FalseClass
            value
          when NilClass
            false
          when Integer
            value != 0
          when String
            value == checked_value
          when Array
            value.include?(checked_value)
          else
            value.to_i != 0
          end
        end

        def radio_button_checked?(value, checked_value)
          value.to_s == checked_value.to_s
        end
      end

      private
        def add_default_name_and_id_for_value(tag_value, options)
          unless tag_value.nil?
            pretty_tag_value = tag_value.to_s.gsub(/\s/, "_").gsub(/\W/, "").downcase
            specified_id = options["id"]
            add_default_name_and_id(options)
            options["id"] += "_#{pretty_tag_value}" unless specified_id
          else
            add_default_name_and_id(options)
          end
        end

        def add_default_name_and_id(options)
          if options.has_key?("index")
            options["name"] ||= tag_name_with_index(options["index"])
            options["id"]   ||= tag_id_with_index(options["index"])
            options.delete("index")
          elsif defined?(@auto_index)
            options["name"] ||= tag_name_with_index(@auto_index)
            options["id"]   ||= tag_id_with_index(@auto_index)
          else
            options["name"] ||= tag_name + (options.has_key?('multiple') ? '[]' : '')
            options["id"]   ||= tag_id
          end
        end

        def tag_name
          "#{@object_name}[#{sanitized_method_name}]"
        end

        def tag_name_with_index(index)
          "#{@object_name}[#{index}][#{sanitized_method_name}]"
        end

        def tag_id
          "#{sanitized_object_name}_#{sanitized_method_name}"
        end

        def tag_id_with_index(index)
          "#{sanitized_object_name}_#{index}_#{sanitized_method_name}"
        end

        def sanitized_object_name
          @sanitized_object_name ||= @object_name.gsub(/\]\[|[^-a-zA-Z0-9:.]/, "_").sub(/_$/, "")
        end

        def sanitized_method_name
          @sanitized_method_name ||= @method_name.sub(/\?$/,"")
        end
    end

    class InstanceTag
      include InstanceTagMethods
    end

    class FormBuilder #:nodoc:
      # The methods which wrap a form helper call.
      class_inheritable_accessor :field_helpers
      self.field_helpers = (FormHelper.instance_methods - ['form_for'])

      attr_accessor :object_name, :object, :options

      def self.model_name
        @model_name ||= Struct.new(:partial_path).new(name.demodulize.underscore.sub!(/_builder$/, ''))
      end

      def to_model
        self
      end

      def initialize(object_name, object, template, options, proc)
        @nested_child_index = {}
        @object_name, @object, @template, @options, @proc = object_name, object, template, options, proc
        @default_options = @options ? @options.slice(:index) : {}
        if @object_name.to_s.match(/\[\]$/)
          if object ||= @template.instance_variable_get("@#{Regexp.last_match.pre_match}") and object.respond_to?(:to_param)
            @auto_index = object.to_param
          else
            raise ArgumentError, "object[] naming but object param and @object var don't exist or don't respond to to_param: #{object.inspect}"
          end
        end
      end

      (field_helpers - %w(label check_box radio_button fields_for hidden_field)).each do |selector|
        src = <<-end_src
          def #{selector}(method, options = {})  # def text_field(method, options = {})
            @template.send(                      #   @template.send(
              #{selector.inspect},               #     "text_field",
              @object_name,                      #     @object_name,
              method,                            #     method,
              objectify_options(options))        #     objectify_options(options))
          end                                    # end
        end_src
        class_eval src, __FILE__, __LINE__
      end

      def fields_for(record_or_name_or_array, *args, &block)
        if options.has_key?(:index)
          index = "[#{options[:index]}]"
        elsif defined?(@auto_index)
          self.object_name = @object_name.to_s.sub(/\[\]$/,"")
          index = "[#{@auto_index}]"
        else
          index = ""
        end

        if options[:builder]
          args << {} unless args.last.is_a?(Hash)
          args.last[:builder] ||= options[:builder]
        end

        case record_or_name_or_array
        when String, Symbol
          if nested_attributes_association?(record_or_name_or_array)
            return fields_for_with_nested_attributes(record_or_name_or_array, args, block)
          else
            name = "#{object_name}#{index}[#{record_or_name_or_array}]"
          end
        when Array
          object = record_or_name_or_array.last
          name = "#{object_name}#{index}[#{ActionController::RecordIdentifier.singular_class_name(object)}]"
          args.unshift(object)
        else
          object = record_or_name_or_array
          name = "#{object_name}#{index}[#{ActionController::RecordIdentifier.singular_class_name(object)}]"
          args.unshift(object)
        end

        @template.fields_for(name, *args, &block)
      end

      def label(method, text = nil, options = {})
        @template.label(@object_name, method, text, objectify_options(options))
      end

      def check_box(method, options = {}, checked_value = "1", unchecked_value = "0")
        @template.check_box(@object_name, method, objectify_options(options), checked_value, unchecked_value)
      end

      def radio_button(method, tag_value, options = {})
        @template.radio_button(@object_name, method, tag_value, objectify_options(options))
      end

      def hidden_field(method, options = {})
        @emitted_hidden_id = true if method == :id
        @template.hidden_field(@object_name, method, objectify_options(options))
      end

      def error_message_on(method, *args)
        @template.error_message_on(@object, method, *args)
      end

      def error_messages(options = {})
        @template.error_messages_for(@object_name, objectify_options(options))
      end

      # Add the submit button for the given form. When no value is given, it checks
      # if the object is a new resource or not to create the proper label:
      #
      #   <% form_for @post do |f| %>
      #     <%= f.submit %>
      #   <% end %>
      # 
      # In the example above, if @post is a new record, it will use "Create Post" as
      # submit button label, otherwise, it uses "Update Post".
      #
      # Those labels can be customized using I18n, under the helpers.submit key and accept
      # the {{model}} as translation interpolation:
      #
      #   en:
      #     helpers:
      #       submit:
      #         create: "Create a {{model}}"
      #         update: "Confirm changes to {{model}}"
      #
      # It also searches for a key specific for the given object:
      #
      #   en:
      #     helpers:
      #       submit:
      #         post:
      #           create: "Add {{model}}"
      #
      def submit(value=nil, options={})
        value, options = nil, value if value.is_a?(Hash)
        value ||= submit_default_value
        @template.submit_tag(value, options.reverse_merge(:id => "#{object_name}_submit"))
      end

      def emitted_hidden_id?
        @emitted_hidden_id
      end

      private
        def objectify_options(options)
          @default_options.merge(options.merge(:object => @object))
        end

        def submit_default_value
          object = @object.respond_to?(:to_model) ? @object.to_model : @object
          key    = object ? (object.new_record? ? :create : :update) : :submit

          model = if object.class.respond_to?(:model_name)
            object.class.model_name.human
          else
            @object_name.to_s.humanize
          end

          defaults = []
          defaults << :"helpers.submit.#{object_name}.#{key}"
          defaults << :"helpers.submit.#{key}"
          defaults << "#{key.to_s.humanize} #{model}"

          I18n.t(defaults.shift, :model => model, :default => defaults)
        end

        def nested_attributes_association?(association_name)
          @object.respond_to?("#{association_name}_attributes=")
        end

        def fields_for_with_nested_attributes(association_name, args, block)
          name = "#{object_name}[#{association_name}_attributes]"
          options = args.extract_options!
          association = args.shift
          association = association.to_model if association.respond_to?(:to_model)

          if association.respond_to?(:new_record?)
            association = [association] if @object.send(association_name).is_a?(Array)
          elsif !association.is_a?(Array)
            association = @object.send(association_name)
          end

          if association.is_a?(Array)
            explicit_child_index = options[:child_index]
            association.map do |child|
              fields_for_nested_model("#{name}[#{explicit_child_index || nested_child_index(name)}]", child, options, block)
            end.join
          elsif association
            fields_for_nested_model(name, association, options, block)
          end
        end

        def fields_for_nested_model(name, object, options, block)
          object = object.to_model if object.respond_to?(:to_model)

          if object.new_record?
            @template.fields_for(name, object, options, &block)
          else
            @template.fields_for(name, object, options) do |builder|
              block.call(builder)
              @template.concat builder.hidden_field(:id) unless builder.emitted_hidden_id?
            end
          end
        end

        def nested_child_index(name)
          @nested_child_index[name] ||= -1
          @nested_child_index[name] += 1
        end
    end
  end

  class Base
    cattr_accessor :default_form_builder
    @@default_form_builder = ::ActionView::Helpers::FormBuilder
  end
end