aboutsummaryrefslogtreecommitdiffstats
path: root/activerecord/lib/active_record/transactions.rb
blob: 08417aaa0f138abe6e17e1a39cf9f7af5ada1cdf (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
module ActiveRecord
  # See ActiveRecord::Transactions::ClassMethods for documentation.
  module Transactions
    extend ActiveSupport::Concern
    #:nodoc:
    ACTIONS = [:create, :destroy, :update]

    included do
      define_callbacks :commit, :rollback,
                       :before_commit,
                       :before_commit_without_transaction_enrollment,
                       :commit_without_transaction_enrollment,
                       :rollback_without_transaction_enrollment,
                       scope: [:kind, :name]
    end

    # = Active Record Transactions
    #
    # \Transactions are protective blocks where SQL statements are only permanent
    # if they can all succeed as one atomic action. The classic example is a
    # transfer between two accounts where you can only have a deposit if the
    # withdrawal succeeded and vice versa. \Transactions enforce the integrity of
    # the database and guard the data against program errors or database
    # break-downs. So basically you should use transaction blocks whenever you
    # have a number of statements that must be executed together or not at all.
    #
    # For example:
    #
    #   ActiveRecord::Base.transaction do
    #     david.withdrawal(100)
    #     mary.deposit(100)
    #   end
    #
    # This example will only take money from David and give it to Mary if neither
    # +withdrawal+ nor +deposit+ raise an exception. Exceptions will force a
    # ROLLBACK that returns the database to the state before the transaction
    # began. Be aware, though, that the objects will _not_ have their instance
    # data returned to their pre-transactional state.
    #
    # == Different Active Record classes in a single transaction
    #
    # Though the #transaction class method is called on some Active Record class,
    # the objects within the transaction block need not all be instances of
    # that class. This is because transactions are per-database connection, not
    # per-model.
    #
    # In this example a +balance+ record is transactionally saved even
    # though #transaction is called on the +Account+ class:
    #
    #   Account.transaction do
    #     balance.save!
    #     account.save!
    #   end
    #
    # The #transaction method is also available as a model instance method.
    # For example, you can also do this:
    #
    #   balance.transaction do
    #     balance.save!
    #     account.save!
    #   end
    #
    # == Transactions are not distributed across database connections
    #
    # A transaction acts on a single database connection. If you have
    # multiple class-specific databases, the transaction will not protect
    # interaction among them. One workaround is to begin a transaction
    # on each class whose models you alter:
    #
    #   Student.transaction do
    #     Course.transaction do
    #       course.enroll(student)
    #       student.units += course.units
    #     end
    #   end
    #
    # This is a poor solution, but fully distributed transactions are beyond
    # the scope of Active Record.
    #
    # == +save+ and +destroy+ are automatically wrapped in a transaction
    #
    # Both {#save}[rdoc-ref:Persistence#save] and
    # {#destroy}[rdoc-ref:Persistence#destroy] come wrapped in a transaction that ensures
    # that whatever you do in validations or callbacks will happen under its
    # protected cover. So you can use validations to check for values that
    # the transaction depends on or you can raise exceptions in the callbacks
    # to rollback, including <tt>after_*</tt> callbacks.
    #
    # As a consequence changes to the database are not seen outside your connection
    # until the operation is complete. For example, if you try to update the index
    # of a search engine in +after_save+ the indexer won't see the updated record.
    # The #after_commit callback is the only one that is triggered once the update
    # is committed. See below.
    #
    # == Exception handling and rolling back
    #
    # Also have in mind that exceptions thrown within a transaction block will
    # be propagated (after triggering the ROLLBACK), so you should be ready to
    # catch those in your application code.
    #
    # One exception is the ActiveRecord::Rollback exception, which will trigger
    # a ROLLBACK when raised, but not be re-raised by the transaction block.
    #
    # *Warning*: one should not catch ActiveRecord::StatementInvalid exceptions
    # inside a transaction block. ActiveRecord::StatementInvalid exceptions indicate that an
    # error occurred at the database level, for example when a unique constraint
    # is violated. On some database systems, such as PostgreSQL, database errors
    # inside a transaction cause the entire transaction to become unusable
    # until it's restarted from the beginning. Here is an example which
    # demonstrates the problem:
    #
    #   # Suppose that we have a Number model with a unique column called 'i'.
    #   Number.transaction do
    #     Number.create(i: 0)
    #     begin
    #       # This will raise a unique constraint error...
    #       Number.create(i: 0)
    #     rescue ActiveRecord::StatementInvalid
    #       # ...which we ignore.
    #     end
    #
    #     # On PostgreSQL, the transaction is now unusable. The following
    #     # statement will cause a PostgreSQL error, even though the unique
    #     # constraint is no longer violated:
    #     Number.create(i: 1)
    #     # => "PGError: ERROR:  current transaction is aborted, commands
    #     #     ignored until end of transaction block"
    #   end
    #
    # One should restart the entire transaction if an
    # ActiveRecord::StatementInvalid occurred.
    #
    # == Nested transactions
    #
    # #transaction calls can be nested. By default, this makes all database
    # statements in the nested transaction block become part of the parent
    # transaction. For example, the following behavior may be surprising:
    #
    #   User.transaction do
    #     User.create(username: 'Kotori')
    #     User.transaction do
    #       User.create(username: 'Nemu')
    #       raise ActiveRecord::Rollback
    #     end
    #   end
    #
    # creates both "Kotori" and "Nemu". Reason is the ActiveRecord::Rollback
    # exception in the nested block does not issue a ROLLBACK. Since these exceptions
    # are captured in transaction blocks, the parent block does not see it and the
    # real transaction is committed.
    #
    # In order to get a ROLLBACK for the nested transaction you may ask for a real
    # sub-transaction by passing <tt>requires_new: true</tt>. If anything goes wrong,
    # the database rolls back to the beginning of the sub-transaction without rolling
    # back the parent transaction. If we add it to the previous example:
    #
    #   User.transaction do
    #     User.create(username: 'Kotori')
    #     User.transaction(requires_new: true) do
    #       User.create(username: 'Nemu')
    #       raise ActiveRecord::Rollback
    #     end
    #   end
    #
    # only "Kotori" is created. This works on MySQL and PostgreSQL. SQLite3 version >= '3.6.8' also supports it.
    #
    # Most databases don't support true nested transactions. At the time of
    # writing, the only database that we're aware of that supports true nested
    # transactions, is MS-SQL. Because of this, Active Record emulates nested
    # transactions by using savepoints on MySQL and PostgreSQL. See
    # http://dev.mysql.com/doc/refman/5.7/en/savepoint.html
    # for more information about savepoints.
    #
    # === \Callbacks
    #
    # There are two types of callbacks associated with committing and rolling back transactions:
    # #after_commit and #after_rollback.
    #
    # #after_commit callbacks are called on every record saved or destroyed within a
    # transaction immediately after the transaction is committed. #after_rollback callbacks
    # are called on every record saved or destroyed within a transaction immediately after the
    # transaction or savepoint is rolled back.
    #
    # These callbacks are useful for interacting with other systems since you will be guaranteed
    # that the callback is only executed when the database is in a permanent state. For example,
    # #after_commit is a good spot to put in a hook to clearing a cache since clearing it from
    # within a transaction could trigger the cache to be regenerated before the database is updated.
    #
    # === Caveats
    #
    # If you're on MySQL, then do not use Data Definition Language(DDL) operations in nested
    # transactions blocks that are emulated with savepoints. That is, do not execute statements
    # like 'CREATE TABLE' inside such blocks. This is because MySQL automatically
    # releases all savepoints upon executing a DDL operation. When +transaction+
    # is finished and tries to release the savepoint it created earlier, a
    # database error will occur because the savepoint has already been
    # automatically released. The following example demonstrates the problem:
    #
    #   Model.connection.transaction do                           # BEGIN
    #     Model.connection.transaction(requires_new: true) do     # CREATE SAVEPOINT active_record_1
    #       Model.connection.create_table(...)                    # active_record_1 now automatically released
    #     end                                                     # RELEASE SAVEPOINT active_record_1
    #                                                             # ^^^^ BOOM! database error!
    #   end
    #
    # Note that "TRUNCATE" is also a MySQL DDL statement!
    module ClassMethods
      # See the ConnectionAdapters::DatabaseStatements#transaction API docs.
      def transaction(options = {}, &block)
        connection.transaction(options, &block)
      end

      def before_commit(*args, &block) # :nodoc:
        set_options_for_callbacks!(args)
        set_callback(:before_commit, :before, *args, &block)
      end

      # This callback is called after a record has been created, updated, or destroyed.
      #
      # You can specify that the callback should only be fired by a certain action with
      # the +:on+ option:
      #
      #   after_commit :do_foo, on: :create
      #   after_commit :do_bar, on: :update
      #   after_commit :do_baz, on: :destroy
      #
      #   after_commit :do_foo_bar, on: [:create, :update]
      #   after_commit :do_bar_baz, on: [:update, :destroy]
      #
      def after_commit(*args, &block)
        set_options_for_callbacks!(args)
        set_callback(:commit, :after, *args, &block)
      end

      # Shortcut for <tt>after_commit :hook, on: :create</tt>.
      def after_create_commit(*args, &block)
        set_options_for_callbacks!(args, on: :create)
        set_callback(:commit, :after, *args, &block)
      end

      # Shortcut for <tt>after_commit :hook, on: :update</tt>.
      def after_update_commit(*args, &block)
        set_options_for_callbacks!(args, on: :update)
        set_callback(:commit, :after, *args, &block)
      end

      # Shortcut for <tt>after_commit :hook, on: :destroy</tt>.
      def after_destroy_commit(*args, &block)
        set_options_for_callbacks!(args, on: :destroy)
        set_callback(:commit, :after, *args, &block)
      end

      # This callback is called after a create, update, or destroy are rolled back.
      #
      # Please check the documentation of #after_commit for options.
      def after_rollback(*args, &block)
        set_options_for_callbacks!(args)
        set_callback(:rollback, :after, *args, &block)
      end

      def before_commit_without_transaction_enrollment(*args, &block) # :nodoc:
        set_options_for_callbacks!(args)
        set_callback(:before_commit_without_transaction_enrollment, :before, *args, &block)
      end

      def after_commit_without_transaction_enrollment(*args, &block) # :nodoc:
        set_options_for_callbacks!(args)
        set_callback(:commit_without_transaction_enrollment, :after, *args, &block)
      end

      def after_rollback_without_transaction_enrollment(*args, &block) # :nodoc:
        set_options_for_callbacks!(args)
        set_callback(:rollback_without_transaction_enrollment, :after, *args, &block)
      end

      private

        def set_options_for_callbacks!(args, enforced_options = {})
          options = args.extract_options!.merge!(enforced_options)
          args << options

          if options[:on]
            fire_on = Array(options[:on])
            assert_valid_transaction_action(fire_on)
            options[:if] = Array(options[:if])
            options[:if] << "transaction_include_any_action?(#{fire_on})"
          end
        end

        def assert_valid_transaction_action(actions)
          if (actions - ACTIONS).any?
            raise ArgumentError, ":on conditions for after_commit and after_rollback callbacks have to be one of #{ACTIONS}"
          end
        end
    end

    # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
    def transaction(options = {}, &block)
      self.class.transaction(options, &block)
    end

    def destroy #:nodoc:
      with_transaction_returning_status { super }
    end

    def save(*) #:nodoc:
      rollback_active_record_state! do
        with_transaction_returning_status { super }
      end
    end

    def save!(*) #:nodoc:
      with_transaction_returning_status { super }
    end

    def touch(*) #:nodoc:
      with_transaction_returning_status { super }
    end

    # Reset id and @new_record if the transaction rolls back.
    def rollback_active_record_state!
      remember_transaction_record_state
      yield
    rescue Exception
      restore_transaction_record_state
      raise
    ensure
      clear_transaction_record_state
    end

    def before_committed! # :nodoc:
      _run_before_commit_without_transaction_enrollment_callbacks
      _run_before_commit_callbacks
    end

    # Call the #after_commit callbacks.
    #
    # Ensure that it is not called if the object was never persisted (failed create),
    # but call it after the commit of a destroyed object.
    def committed!(should_run_callbacks: true) #:nodoc:
      if should_run_callbacks && destroyed? || persisted?
        _run_commit_without_transaction_enrollment_callbacks
        _run_commit_callbacks
      end
    ensure
      force_clear_transaction_record_state
    end

    # Call the #after_rollback callbacks. The +force_restore_state+ argument indicates if the record
    # state should be rolled back to the beginning or just to the last savepoint.
    def rolledback!(force_restore_state: false, should_run_callbacks: true) #:nodoc:
      if should_run_callbacks
        _run_rollback_callbacks
        _run_rollback_without_transaction_enrollment_callbacks
      end
    ensure
      restore_transaction_record_state(force_restore_state)
      clear_transaction_record_state
    end

    # Add the record to the current transaction so that the #after_rollback and #after_commit callbacks
    # can be called.
    def add_to_transaction
      if has_transactional_callbacks?
        self.class.connection.add_transaction_record(self)
      else
        sync_with_transaction_state
        set_transaction_state(self.class.connection.transaction_state)
      end
      remember_transaction_record_state
    end

    # Executes +method+ within a transaction and captures its return value as a
    # status flag. If the status is true the transaction is committed, otherwise
    # a ROLLBACK is issued. In any case the status flag is returned.
    #
    # This method is available within the context of an ActiveRecord::Base
    # instance.
    def with_transaction_returning_status
      status = nil
      self.class.transaction do
        add_to_transaction
        begin
          status = yield
        rescue ActiveRecord::Rollback
          clear_transaction_record_state
          status = nil
        end

        raise ActiveRecord::Rollback unless status
      end
      status
    ensure
      if @transaction_state && @transaction_state.committed?
        clear_transaction_record_state
      end
    end

    private

      # Save the new record state and id of a record so it can be restored later if a transaction fails.
      def remember_transaction_record_state
        @_start_transaction_state[:id] = id
        @_start_transaction_state.reverse_merge!(
          new_record: @new_record,
          destroyed: @destroyed,
          frozen?: frozen?,
        )
        @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) + 1
      end

      # Clear the new record state and id of a record.
      def clear_transaction_record_state
        @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
        force_clear_transaction_record_state if @_start_transaction_state[:level] < 1
      end

      # Force to clear the transaction record state.
      def force_clear_transaction_record_state
        @_start_transaction_state.clear
      end

      # Restore the new record state and id of a record that was previously saved by a call to save_record_state.
      def restore_transaction_record_state(force = false)
        unless @_start_transaction_state.empty?
          transaction_level = (@_start_transaction_state[:level] || 0) - 1
          if transaction_level < 1 || force
            restore_state = @_start_transaction_state
            thaw
            @new_record = restore_state[:new_record]
            @destroyed  = restore_state[:destroyed]
            pk = self.class.primary_key
            if pk && read_attribute(pk) != restore_state[:id]
              write_attribute(pk, restore_state[:id])
            end
            freeze if restore_state[:frozen?]
          end
        end
      end

      # Determine if a record was created or destroyed in a transaction. State should be one of :new_record or :destroyed.
      def transaction_record_state(state)
        @_start_transaction_state[state]
      end

      # Determine if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.
      def transaction_include_any_action?(actions)
        actions.any? do |action|
          case action
          when :create
            transaction_record_state(:new_record)
          when :destroy
            defined?(@_trigger_destroy_callback) && @_trigger_destroy_callback
          when :update
            !(transaction_record_state(:new_record) || destroyed?) &&
              (defined?(@_trigger_update_callback) && @_trigger_update_callback)
          end
        end
      end

      def set_transaction_state(state)
        @transaction_state = state
      end

      def has_transactional_callbacks?
        !_rollback_callbacks.empty? || !_commit_callbacks.empty? || !_before_commit_callbacks.empty?
      end

      # Updates the attributes on this particular Active Record object so that
      # if it's associated with a transaction, then the state of the Active Record
      # object will be updated to reflect the current state of the transaction.
      #
      # The +@transaction_state+ variable stores the states of the associated
      # transaction. This relies on the fact that a transaction can only be in
      # one rollback or commit (otherwise a list of states would be required).
      # Each Active Record object inside of a transaction carries that transaction's
      # TransactionState.
      #
      # This method checks to see if the ActiveRecord object's state reflects
      # the TransactionState, and rolls back or commits the Active Record object
      # as appropriate.
      #
      # Since Active Record objects can be inside multiple transactions, this
      # method recursively goes through the parent of the TransactionState and
      # checks if the Active Record object reflects the state of the object.
      def sync_with_transaction_state
        update_attributes_from_transaction_state(@transaction_state)
      end

      def update_attributes_from_transaction_state(transaction_state)
        if transaction_state && transaction_state.finalized?
          restore_transaction_record_state if transaction_state.rolledback?
          clear_transaction_record_state
        end
      end
  end
end