aboutsummaryrefslogtreecommitdiffstats
path: root/activerecord/CHANGELOG.md
blob: 50a0b291b313b2f5c622ac842f032eeb74332fbb (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
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
*   `ActiveRecord::Relation#reverse_order` throws `ActiveRecord::IrreversibleOrderError`
    when the order can not be reversed using current trivial algorithm.
    Also raises the same error when `#reverse_order` is called on
    relation without any order and table has no primary key:

        Topic.order("concat(author_name, title)").reverse_order
          # Before: SELECT `topics`.* FROM `topics` ORDER BY concat(author_name DESC, title) DESC
          # After: raises ActiveRecord::IrreversibleOrderError
        Edge.all.reverse_order
          # Before: SELECT `edges`.* FROM `edges` ORDER BY `edges`.`` DESC
          # After: raises ActiveRecord::IrreversibleOrderError

    *Bogdan Gusiev*

*   Improve schema_migrations insertion performance by inserting all versions
    in one INSERT SQL.

    *Akira Matsuda*, *Naoto Koshikawa*

*   Using `references` or `belongs_to` in migrations will always add index
    for the referenced column by default, without adding `index: true` option
    to generated migration file. Users can opt out of this by passing
    `index: false`.

    Fixes #18146.

    *Matthew Draper*, *Prathamesh Sonpatki*

*   Run `type` attributes through attributes API type-casting before
    instantiating the corresponding subclass. This makes it possible to define
    custom STI mappings.

    Fixes #21986.

    *Yves Senn*

*   Don't try to quote functions or expressions passed to `:default` option if
    they are passed as procs.

    This will generate proper query with the passed function or expression for
    the default option, instead of trying to quote it in incorrect fashion.

    Example:

        create_table :posts do |t|
          t.datetime :published_at, default: -> { 'NOW()' }
        end

    *Ryuta Kamizono*

*   Fix regression when loading fixture files with symbol keys.

    Fixes #22584.

    *Yves Senn*

*   Use `version` column as primary key for schema_migrations table because
    `schema_migrations` versions are guaranteed to be unique.

    This makes it possible to use `update_attributes` on models that do
    not have a primary key.

    *Richard Schneeman*

*   Add short-hand methods for text and blob types in MySQL.

    In Pg and Sqlite3, `:text` and `:binary` have variable unlimited length.
    But in MySQL, these have limited length for each types (ref #21591, #21619).
    This change adds short-hand methods for each text and blob types.

    Example:

        create_table :foos do |t|
          t.tinyblob   :tiny_blob
          t.mediumblob :medium_blob
          t.longblob   :long_blob
          t.tinytext   :tiny_text
          t.mediumtext :medium_text
          t.longtext   :long_text
        end

    *Ryuta Kamizono*

*   Take into account UTC offset when assigning string representation of
    timestamp with offset specified to attribute of time type.

    *Andrey Novikov*

*   When calling `first` with a `limit` argument, return directly from the
    `loaded?` records if available.

    *Ben Woosley*

*   Deprecate sending the `offset` argument to `find_nth`. Please use the
    `offset` method on relation instead.

    *Ben Woosley*

## Rails 5.0.0.beta1 (December 18, 2015) ##

*   Order the result of `find(ids)` to match the passed array, if the relation
    has no explicit order defined.

    Fixes #20338.

    *Miguel Grazziotin*, *Matthew Draper*

*   Omit default limit values in dumped schema. It's tidier, and if the defaults
    change in the future, we can address that via Migration API Versioning.

    *Jean Boussier*

*   Support passing the schema name as a prefix to table name in
    `ConnectionAdapters::SchemaStatements#indexes`. Previously the prefix would
    be considered a full part of the index name, and only the schema in the
    current search path would be considered.

    *Grey Baker*

*   Ignore index name in `index_exists?` and `remove_index` when not passed a
    name to check for.

    *Grey Baker*

*   Extract support for the legacy `mysql` database adapter from core. It will
    live on in a separate gem for now, but most users should just use `mysql2`.

    *Abdelkader Boudih*

*   ApplicationRecord is a new superclass for all app models, analogous to app
    controllers subclassing ApplicationController instead of
    ActionController::Base. This gives apps a single spot to configure app-wide
    model behavior.

    Newly generated applications have `app/models/application_record.rb`
    present by default.

    *Genadi Samokovarov*

*   Version the API presented to migration classes, so we can change parameter
    defaults without breaking existing migrations, or forcing them to be
    rewritten through a deprecation cycle.

    New migrations specify the Rails version they were written for:

        class AddStatusToOrders < ActiveRecord::Migration[5.0]
          def change
            # ...
          end
        end

    *Matthew Draper*, *Ravil Bayramgalin*

*   Use bind params for `limit` and `offset`. This will generate significantly
    fewer prepared statements for common tasks like pagination. To support this
    change, passing a string containing a comma to `limit` has been deprecated,
    and passing an Arel node to `limit` is no longer supported.

    Fixes #22250.

    *Sean Griffin*

*   Introduce after_{create,update,delete}_commit callbacks.

    Before:

        after_commit :add_to_index_later, on: :create
        after_commit :update_in_index_later, on: :update
        after_commit :remove_from_index_later, on: :destroy

    After:

        after_create_commit  :add_to_index_later
        after_update_commit  :update_in_index_later
        after_destroy_commit :remove_from_index_later

    Fixes #22515.

    *Genadi Samokovarov*

*   Respect the column default values for `inheritance_column` when
    instantiating records through the base class.

    Fixes #17121.

    Example:

        # The schema of BaseModel has `t.string :type, default: 'SubType'`
        subtype = BaseModel.new
        assert_equals SubType, subtype.class

    *Kuldeep Aggarwal*

*   Fix `rake db:structure:dump` on Postgres when multiple schemas are used.

    Fixes #22346.

    *Nick Muerdter*, *ckoenig*

*   Add schema dumping support for PostgreSQL geometric data types.

    *Ryuta Kamizono*

*   Except keys of `build_record`'s argument from `create_scope` in `initialize_attributes`.

    Fixes #21893.

    *Yuichiro Kaneko*

*   Deprecate `connection.tables` on the SQLite3 and MySQL adapters.
    Also deprecate passing arguments to `#tables`.
    And deprecate `table_exists?`.

    The `#tables` method of some adapters (mysql, mysql2, sqlite3) would return
    both tables and views while others (postgresql) just return tables. To make
    their behavior consistent, `#tables` will return only tables in the future.

    The `#table_exists?` method would check both tables and views. To make
    their behavior consistent with `#tables`, `#table_exists?` will check only
    tables in the future.

    *Yuichiro Kaneko*

*   Improve support for non Active Record objects on `validates_associated`

    Skipping `marked_for_destruction?` when the associated object does not responds
    to it make easier to validate virtual associations built on top of Active Model
    objects and/or serialized objects that implement a `valid?` instance method.

    *Kassio Borges*, *Lucas Mazza*

*   Change connection management middleware to return a new response with
    a body proxy, rather than mutating the original.

    *Kevin Buchanan*

*   Make `db:migrate:status` to render `1_some.rb` format migrate files.

    These files are in `db/migrate`:

        * 1_valid_people_have_last_names.rb
        * 20150819202140_irreversible_migration.rb
        * 20150823202140_add_admin_flag_to_users.rb
        * 20150823202141_migration_tests.rb
        * 2_we_need_reminders.rb
        * 3_innocent_jointable.rb

    Before:

        $ bundle exec rake db:migrate:status
        ...

         Status   Migration ID    Migration Name
        --------------------------------------------------
           up     001             ********** NO FILE **********
           up     002             ********** NO FILE **********
           up     003             ********** NO FILE **********
           up     20150819202140  Irreversible migration
           up     20150823202140  Add admin flag to users
           up     20150823202141  Migration tests

    After:

        $ bundle exec rake db:migrate:status
        ...

         Status   Migration ID    Migration Name
        --------------------------------------------------
           up     001             Valid people have last names
           up     002             We need reminders
           up     003             Innocent jointable
           up     20150819202140  Irreversible migration
           up     20150823202140  Add admin flag to users
           up     20150823202141  Migration tests

    *Yuichiro Kaneko*

*   Define `ActiveRecord::Sanitization.sanitize_sql_for_order` and use it inside
    `preprocess_order_args`.

    *Yuichiro Kaneko*

*   Allow bigint with default nil for avoiding auto increment primary key.

    *Ryuta Kamizono*

*   Remove `DEFAULT_CHARSET` and `DEFAULT_COLLATION` in `MySQLDatabaseTasks`.

    We should omit the collation entirely rather than providing a default.
    Then the choice is the responsibility of the server and MySQL distribution.

    *Ryuta Kamizono*

*   Alias `ActiveRecord::Relation#left_joins` to
    `ActiveRecord::Relation#left_outer_joins`.

    *Takashi Kokubun*

*   Use advisory locking to raise a `ConcurrentMigrationError` instead of
    attempting to migrate when another migration is currently running.

    *Sam Davies*

*   Added `ActiveRecord::Relation#left_outer_joins`.

    Example:

        User.left_outer_joins(:posts)
        # => SELECT "users".* FROM "users" LEFT OUTER JOIN "posts" ON
             "posts"."user_id" = "users"."id"

    *Florian Thomas*

*   Support passing an array to `order` for SQL parameter sanitization.

    *Aaron Suggs*

*   Avoid disabling errors on the PostgreSQL connection when enabling the
    `standard_conforming_strings` setting. Errors were previously disabled because
    the setting wasn't writable in Postgres 8.1 and didn't exist in earlier
    versions. Now Rails only supports Postgres 8.2+ we're fine to assume the
    setting exists. Disabling errors caused problems when using a connection
    pooling tool like PgBouncer because it's not guaranteed to have the same
    connection between calls to `execute` and it could leave the connection
    with errors disabled.

    Fixes #22101.

    *Harry Marr*

*   Set `scope.reordering_value` to `true` if `:reordering`-values are specified.

    Fixes #21886.

    *Hiroaki Izu*

*   Add support for bidirectional destroy dependencies.

    Fixes #13609.

    Example:

        class Content < ActiveRecord::Base
          has_one :position, dependent: :destroy
        end

        class Position < ActiveRecord::Base
          belongs_to :content, dependent: :destroy
        end

    *Seb Jacobs*

*   Includes HABTM returns correct size now. It's caused by the join dependency
    only instantiates one HABTM object because the join table hasn't a primary key.

    Fixes #16032.

    Examples:

        before:

        Project.first.salaried_developers.size # => 3
        Project.includes(:salaried_developers).first.salaried_developers.size # => 1

        after:

        Project.first.salaried_developers.size # => 3
        Project.includes(:salaried_developers).first.salaried_developers.size # => 3

    *Bigxiang*

*   Add option to index errors in nested attributes

    For models which have nested attributes, errors within those models will
    now be indexed if :index_errors is specified when defining a
    has_many relationship, or if its set in the global config.

    Example:

        class Guitar < ActiveRecord::Base
          has_many :tuning_pegs
          accepts_nested_attributes_for :tuning_pegs
        end

        class TuningPeg < ActiveRecord::Base
          belongs_to :guitar
          validates_numericality_of :pitch
        end

        # Old style
        guitar.errors["tuning_pegs.pitch"] = ["is not a number"]

        # New style (if defined globally, or set in has_many_relationship)
        guitar.errors["tuning_pegs[1].pitch"] = ["is not a number"]

    *Michael Probber*, *Terence Sun*

*   Exit with non-zero status for failed database rake tasks.

    *Jay Hayes*

*   Queries such as `Computer.joins(:monitor).group(:status).count` will now be
    interpreted as  `Computer.joins(:monitor).group('computers.status').count`
    so that when `Computer` and `Monitor` have both `status` columns we don't
    have conflicts in projection.

    *Rafael Sales*

*   Add ability to default to `uuid` as primary key when generating database migrations.

    Example:

        config.generators do |g|
          g.orm :active_record, primary_key_type: :uuid
        end

    *Jon McCartie*

*   Don't cache arguments in `#find_by` if they are an `ActiveRecord::Relation`.

    Fixes #20817.

    *Hiroaki Izu*

*   Qualify column name inserted by `group` in calculation.

    Giving `group` an unqualified column name now works, even if the relation
    has `JOIN` with another table which also has a column of the name.

    *Soutaro Matsumoto*

*   Don't cache prepared statements containing an IN clause or a SQL literal, as
    these queries will change often and are unlikely to have a cache hit.

    *Sean Griffin*

*   Fix `rewhere` in a `has_many` association.

    Fixes #21955.

    *Josh Branchaud*, *Kal*

*   `where` raises ArgumentError on unsupported types.

    Fixes #20473.

    *Jake Worth*

*   Add an immutable string type to help reduce memory usage for apps which do
    not need mutation detection on strings.

    *Sean Griffin*

*   Give `ActiveRecord::Relation#update` its own deprecation warning when
    passed an `ActiveRecord::Base` instance.

    Fixes #21945.

    *Ted Johansson*

*   Make it possible to pass `:to_table` when adding a foreign key through
    `add_reference`.

    Fixes #21563.

    *Yves Senn*

*   No longer pass deprecated option `-i` to `pg_dump`.

    *Paul Sadauskas*

*   Concurrent `AR::Base#increment!` and `#decrement!` on the same record
    are all reflected in the database rather than overwriting each other.

    *Bogdan Gusiev*

*   Avoid leaking the first relation we call `first` on, per model.

    Fixes #21921.

    *Matthew Draper*, *Jean Boussier*

*   Remove unused `pk_and_sequence_for` in `AbstractMysqlAdapter`.

    *Ryuta Kamizono*

*   Allow fixtures files to set the model class in the YAML file itself.

    To load the fixtures file `accounts.yml` as the `User` model, use:

        _fixture:
          model_class: User
        david:
          name: David

    Fixes #9516.

    *Roque Pinel*

*   Don't require a database connection to load a class which uses acceptance
    validations.

    *Sean Griffin*

*   Correctly apply `unscope` when preloading through associations.

    *Jimmy Bourassa*

*   Fixed taking precision into count when assigning a value to timestamp attribute.

    Timestamp column can have less precision than ruby timestamp
    In result in how big a fraction of a second can be stored in the
    database.


        m = Model.create!
        m.created_at.usec == m.reload.created_at.usec # => false
        # due to different precision in Time.now and database column

    If the precision is low enough, (mysql default is 0, so it is always low
    enough by default) the value changes when model is reloaded from the
    database. This patch fixes that issue ensuring that any timestamp
    assigned as an attribute is converted to column precision under the
    attribute.

    *Bogdan Gusiev*

*   Introduce `connection.data_sources` and `connection.data_source_exists?`.
    These methods determine what relations can be used to back Active Record
    models (usually tables and views).

    Also deprecate `SchemaCache#tables`, `SchemaCache#table_exists?` and
    `SchemaCache#clear_table_cache!` in favor of their new data source
    counterparts.

    *Yves Senn*, *Matthew Draper*

*   Add `ActiveRecord::Base.ignored_columns` to make some columns
    invisible from Active Record.

    *Jean Boussier*

*   `ActiveRecord::Tasks::MySQLDatabaseTasks` fails if shellout to
    mysql commands (like `mysqldump`) is not successful.

    *Steve Mitchell*

*   Ensure `select` quotes aliased attributes, even when using `from`.

    Fixes #21488.

    *Sean Griffin*, *@johanlunds*

*   MySQL: support `unsigned` numeric data types.

    Example:

        create_table :foos do |t|
          t.unsigned_integer :quantity
          t.unsigned_bigint  :total
          t.unsigned_float   :percentage
          t.unsigned_decimal :price, precision: 10, scale: 2
        end

    The `unsigned: true` option may be used for the primary key:

        create_table :foos, id: :bigint, unsigned: true do |t|
          …
        end

    *Ryuta Kamizono*

*   Add `#views` and `#view_exists?` methods on connection adapters.

    *Ryuta Kamizono*

*   Correctly dump composite primary key.

    Example:

        create_table :barcodes, primary_key: ["region", "code"] do |t|
          t.string :region
          t.integer :code
        end

    *Ryuta Kamizono*

*   Lookup the attribute name for `restrict_with_error` messages on the
    model class that defines the association.

    *kuboon*, *Ronak Jangir*

*   Correct query for PostgreSQL 8.2 compatibility.

    *Ben Murphy*, *Matthew Draper*

*   `bin/rake db:migrate` uses
    `ActiveRecord::Tasks::DatabaseTasks.migrations_paths` instead of
    `Migrator.migrations_paths`.

    *Tobias Bielohlawek*

*   Support dropping indexes concurrently in PostgreSQL.

    See http://www.postgresql.org/docs/9.4/static/sql-dropindex.html for more
    details.

    *Grey Baker*

*   Deprecate passing conditions to `ActiveRecord::Relation#delete_all`
    and `ActiveRecord::Relation#destroy_all`.

    *Wojciech Wnętrzak*

*   Instantiating an AR model with `ActionController::Parameters` now raises
    an `ActiveModel::ForbiddenAttributesError` if the parameters include a
    `type` field that has not been explicitly permitted. Previously, the
    `type` field was simply ignored in the same situation.

    *Prem Sichanugrist*

*   PostgreSQL, `create_schema`, `drop_schema` and `rename_table` now quote
    schema names.

    Fixes #21418.

    Example:

        create_schema("my.schema")
        # CREATE SCHEMA "my.schema";

    *Yves Senn*

*   PostgreSQL, add `:if_exists` option to `#drop_schema`. This makes it
    possible to drop a schema that might exist without raising an exception if
    it doesn't.

    *Yves Senn*

*   Only try to nullify has_one target association if the record is persisted.

    Fixes #21223.

    *Agis Anastasopoulos*

*   Uniqueness validator raises descriptive error when running on a persisted
    record without primary key.

    Fixes #21304.

    *Yves Senn*

*   Add a native JSON data type support in MySQL.

    Example:

        create_table :json_data_type do |t|
          t.json :settings
        end

    *Ryuta Kamizono*

*   Descriptive error message when fixtures contain a missing column.

    Fixes #21201.

    *Yves Senn*

*   `ActiveRecord::Tasks::PostgreSQLDatabaseTasks` fail if shellout to
    postgresql commands (like `pg_dump`) is not successful.

    *Bryan Paxton*, *Nate Berkopec*

*   Add `ActiveRecord::Relation#in_batches` to work with records and relations
    in batches.

    Available options are `of` (batch size), `load`, `start`, and `finish`.

    Examples:

        Person.in_batches.each_record(&:party_all_night!)
        Person.in_batches.update_all(awesome: true)
        Person.in_batches.delete_all
        Person.in_batches.each do |relation|
          relation.delete_all
          sleep 10 # Throttles the delete queries
        end

    Fixes #20933.

    *Sina Siadat*

*   Added methods for PostgreSQL geometric data types to use in migrations.

    Example:

        create_table :foo do |t|
          t.line :foo_line
          t.lseg :foo_lseg
          t.box :foo_box
          t.path :foo_path
          t.polygon :foo_polygon
          t.circle :foo_circle
        end

    *Mehmet Emin İNAÇ*

*   Add `cache_key` to ActiveRecord::Relation.

    Example:

        @users = User.where("name like ?", "%Alberto%")
        @users.cache_key
        # => "/users/query-5942b155a43b139f2471b872ac54251f-3-20150714212107656125000"

    *Alberto Fernández-Capel*

*   Properly allow uniqueness validations on primary keys.

    Fixes #20966.

    *Sean Griffin*, *presskey*

*   Don't raise an error if an association failed to destroy when `destroy` was
    called on the parent (as opposed to `destroy!`).

    Fixes #20991.

    *Sean Griffin*

*   `ActiveRecord::RecordNotFound` modified to store model name, primary_key and
    id of the caller model. It allows the catcher of this exception to make
    a better decision to what to do with it.

    Example:

        class SomeAbstractController < ActionController::Base
          rescue_from ActiveRecord::RecordNotFound, with: :redirect_to_404

          private def redirect_to_404(e)
            return redirect_to(posts_url) if e.model == 'Post'
            raise
          end
        end

    *Sameer Rahmani*

*   Deprecate the keys for association `restrict_dependent_destroy` errors in favor
    of new key names.

    Previously `has_one` and `has_many` associations were using the
    `one` and `many` keys respectively. Both of these keys have special
    meaning in I18n (they are considered to be pluralizations) so by
    renaming them to `has_one` and `has_many` we make the messages more explicit
    and most importantly they don't clash with linguistical systems that need to
    validate translation keys (and their pluralizations).

    The `:'restrict_dependent_destroy.one'` key should be replaced with
    `:'restrict_dependent_destroy.has_one'`, and `:'restrict_dependent_destroy.many'`
    with `:'restrict_dependent_destroy.has_many'`.

    *Roque Pinel*, *Christopher Dell*

*   Fix state being carried over from previous transaction.

    Considering the following example where `name` is a required attribute.
    Before we had `new_record?` returning `true` for a persisted record:

        author = Author.create! name: 'foo'
        author.name = nil
        author.save        # => false
        author.new_record? # => true

    Fixes #20824.

    *Roque Pinel*

*   Correctly ignore `mark_for_destruction` when `autosave` isn't set to `true`
    when validating associations.

    Fixes #20882.

    *Sean Griffin*

*   Fix a bug where counter_cache doesn't always work with polymorphic
    relations.

    Fixes #16407.

    *Stefan Kanev*, *Sean Griffin*

*   Ensure that cyclic associations with autosave don't cause duplicate errors
    to be added to the parent record.

    Fixes #20874.

    *Sean Griffin*

*   Ensure that `ActionController::Parameters` can still be passed to nested
    attributes.

    Fixes #20922.

    *Sean Griffin*

*   Deprecate force association reload by passing a truthy argument to
    association method.

    For collection association, you can call `#reload` on association proxy to
    force a reload:

        @user.posts.reload   # Instead of @user.posts(true)

    For singular association, you can call `#reload` on the parent object to
    clear its association cache then call the association method:

        @user.reload.profile   # Instead of @user.profile(true)

    Passing a truthy argument to force association to reload will be removed in
    Rails 5.1.

    *Prem Sichanugrist*

*   Replaced `ActiveSupport::Concurrency::Latch` with `Concurrent::CountDownLatch`
    from the concurrent-ruby gem.

    *Jerry D'Antonio*

*   Fix through associations using scopes having the scope merged multiple
    times.

    Fixes #20721.
    Fixes #20727.

    *Sean Griffin*

*   `ActiveRecord::Base.dump_schema_after_migration` applies migration tasks
    other than `db:migrate`. (eg. `db:rollback`, `db:migrate:dup`, ...)

    Fixes #20743.

    *Yves Senn*

*   Add alternate syntax to make `change_column_default` reversible.

    User can pass in `:from` and `:to` to make `change_column_default` command
    become reversible.

    Example:

        change_column_default :posts, :status, from: nil, to: "draft"
        change_column_default :users, :authorized, from: true, to: false

    *Prem Sichanugrist*

*   Prevent error when using `force_reload: true` on an unassigned polymorphic
    belongs_to association.

    Fixes #20426.

    *James Dabbs*

*   Correctly raise `ActiveRecord::AssociationTypeMismatch` when assigning
    a wrong type to a namespaced association.

    Fixes #20545.

    *Diego Carrion*

*   `validates_absence_of` respects `marked_for_destruction?`.

    Fixes #20449.

    *Yves Senn*

*   Include the `Enumerable` module in `ActiveRecord::Relation`

    *Sean Griffin*, *bogdan*

*   Use `Enumerable#sum` in `ActiveRecord::Relation` if a block is given.

    *Sean Griffin*

*   Let `WITH` queries (Common Table Expressions) be explainable.

    *Vladimir Kochnev*

*   Make `remove_index :table, :column` reversible.

    *Yves Senn*

*   Fixed an error which would occur in dirty checking when calling
    `update_attributes` from a getter.

    Fixes #20531.

    *Sean Griffin*

*   Make `remove_foreign_key` reversible. Any foreign key options must be
    specified, similar to `remove_column`.

    *Aster Ryan*

*   Add `:_prefix` and `:_suffix` options to `enum` definition.

    Fixes #17511, #17415.

    *Igor Kapkov*

*   Correctly handle decimal arrays with defaults in the schema dumper.

    Fixes #20515.

    *Sean Griffin*, *jmondo*

*   Deprecate the PostgreSQL `:point` type in favor of a new one which will return
    `Point` objects instead of an `Array`

    *Sean Griffin*

*   Ensure symbols passed to `ActiveRecord::Relation#select` are always treated
    as columns.

    Fixes #20360.

    *Sean Griffin*

*   Do not set `sql_mode` if `strict: :default` is specified.

        # config/database.yml
        production:
          adapter: mysql2
          database: foo_prod
          user: foo
          strict: :default

    *Ryuta Kamizono*

*   Allow proc defaults to be passed to the attributes API. See documentation
    for examples.

    *Sean Griffin*, *Kir Shatrov*

*   SQLite: `:collation` support for string and text columns.

    Example:

        create_table :foo do |t|
          t.string :string_nocase, collation: 'NOCASE'
          t.text :text_rtrim, collation: 'RTRIM'
        end

        add_column :foo, :title, :string, collation: 'RTRIM'

        change_column :foo, :title, :string, collation: 'NOCASE'

    *Akshay Vishnoi*

*   Allow the use of symbols or strings to specify enum values in test
    fixtures:

        awdr:
          title: "Agile Web Development with Rails"
          status: :proposed

    *George Claghorn*

*   Clear query cache when `ActiveRecord::Base#reload` is called.

    *Shane Hender, Pierre Nespo*

*   Include stored procedures and function on the MySQL structure dump.

    *Jonathan Worek*

*   Pass `:extend` option for `has_and_belongs_to_many` associations to the
    underlying `has_many :through`.

    *Jaehyun Shin*

*   Deprecate `Relation#uniq` use `Relation#distinct` instead.

    See #9683.

    *Yves Senn*

*   Allow single table inheritance instantiation to work when storing
    demodulized class names.

    *Alex Robbin*

*   Correctly pass MySQL options when using `structure_dump` or
    `structure_load`.

    Specifically, it fixes an issue when using SSL authentication.

    *Alex Coomans*

*   Dump indexes in `create_table` instead of `add_index`.

    If the adapter supports indexes in `create_table`, generated SQL is
    slightly more efficient.

    *Ryuta Kamizono*

*   Correctly dump `:options` on `create_table` for MySQL.

    *Ryuta Kamizono*

*   PostgreSQL: `:collation` support for string and text columns.

    Example:

        create_table :foos do |t|
          t.string :string_en, collation: 'en_US.UTF-8'
          t.text   :text_ja,   collation: 'ja_JP.UTF-8'
        end

    *Ryuta Kamizono*

*   Remove `ActiveRecord::Serialization::XmlSerializer` from core.

    *Zachary Scott*

*   Make `unscope` aware of "less than" and "greater than" conditions.

    *TAKAHASHI Kazuaki*

*   `find_by` and `find_by!` raise `ArgumentError` when called without
    arguments.

    *Kohei Suzuki*

*   Revert behavior of `db:schema:load` back to loading the full
    environment. This ensures that initializers are run.

    Fixes #19545.

    *Yves Senn*

*   Fix missing index when using `timestamps` with the `index` option.

    The `index` option used with `timestamps` should be passed to both
    `column` definitions for `created_at` and `updated_at` rather than just
    the first.

    *Paul Mucur*

*   Rename `:class` to `:anonymous_class` in association options.

    Fixes #19659.

    *Andrew White*

*   Autosave existing records on a has many through association when the parent
    is new.

    Fixes #19782.

    *Sean Griffin*

*   Fixed a bug where uniqueness validations would error on out of range values,
    even if an validation should have prevented it from hitting the database.

    *Andrey Voronkov*

*   MySQL: `:charset` and `:collation` support for string and text columns.

    Example:

        create_table :foos do |t|
          t.string :string_utf8_bin, charset: 'utf8', collation: 'utf8_bin'
          t.text   :text_ascii,      charset: 'ascii'
        end

    *Ryuta Kamizono*

*   Foreign key related methods in the migration DSL respect
    `ActiveRecord::Base.pluralize_table_names = false`.

    Fixes #19643.

    *Mehmet Emin İNAÇ*

*   Reduce memory usage from loading types on PostgreSQL.

    Fixes #19578.

    *Sean Griffin*

*   Add `config.active_record.warn_on_records_fetched_greater_than` option.

    When set to an integer, a warning will be logged whenever a result set
    larger than the specified size is returned by a query.

    Fixes #16463.

    *Jason Nochlin*

*   Ignore `.psqlrc` when loading database structure.

    *Jason Weathered*

*   Fix referencing wrong table aliases while joining tables of has many through
    association (only when calling calculation methods).

    Fixes #19276.

    *pinglamb*

*   Correctly persist a serialized attribute that has been returned to
    its default value by an in-place modification.

    Fixes #19467.

    *Matthew Draper*

*   Fix generating the schema file when using PostgreSQL `BigInt[]` data type.
    Previously the `limit: 8` was not coming through, and this caused it to
    become `Int[]` data type after rebuilding from the schema.

    Fixes #19420.

    *Jake Waller*

*   Reuse the `CollectionAssociation#reader` cache when the foreign key is
    available prior to save.

    *Ben Woosley*

*   Add `config.active_record.dump_schemas` to fix `db:structure:dump`
    when using schema_search_path and PostgreSQL extensions.

    Fixes #17157.

    *Ryan Wallace*

*   Renaming `use_transactional_fixtures` to `use_transactional_tests` for clarity.

    Fixes #18864.

    *Brandon Weiss*

*   Increase pg gem version requirement to `~> 0.18`. Earlier versions of the
    pg gem are known to have problems with Ruby 2.2.

    *Matt Brictson*

*   Correctly dump `serial` and `bigserial`.

    *Ryuta Kamizono*

*   Fix default `format` value in `ActiveRecord::Tasks::DatabaseTasks#schema_file`.

    *James Cox*

*   Don't enroll records in the transaction if they don't have commit callbacks.
    This was causing a memory leak when creating many records inside a transaction.

    Fixes #15549.

    *Will Bryant*, *Aaron Patterson*

*   Correctly create through records when created on a has many through
    association when using `where`.

    Fixes #19073.

    *Sean Griffin*

*   Add `SchemaMigration.create_table` support for any unicode charsets with MySQL.

    *Ryuta Kamizono*

*   PostgreSQL no longer disables user triggers if system triggers can't be
    disabled. Disabling user triggers does not fulfill what the method promises.
    Rails currently requires superuser privileges for this method.

    If you absolutely rely on this behavior, consider patching
    `disable_referential_integrity`.

    *Yves Senn*

*   Restore aborted transaction state when `disable_referential_integrity` fails
    due to missing permissions.

    *Toby Ovod-Everett*, *Yves Senn*

*   In PostgreSQL, print a warning message if `disable_referential_integrity`
    fails due to missing permissions.

    *Andrey Nering*, *Yves Senn*

*   Allow a `:limit` option for MySQL bigint primary key support.

    Example:

        create_table :foos, id: :primary_key, limit: 8 do |t|
        end

        # or

        create_table :foos, id: false do |t|
          t.primary_key :id, limit: 8
        end

    *Ryuta Kamizono*

*   `belongs_to` will now trigger a validation error by default if the association is not present.
    You can turn this off on a per-association basis with `optional: true`.
    (Note this new default only applies to new Rails apps that will be generated with
    `config.active_record.belongs_to_required_by_default = true` in initializer.)

    *Josef Šimánek*

*   Fixed `ActiveRecord::Relation#becomes!` and `changed_attributes` issues for type
    columns.

    Fixes #17139.

    *Miklos Fazekas*

*   Format the time string according to the precision of the time column.

    *Ryuta Kamizono*

*   Allow a `:precision` option for time type columns.

    *Ryuta Kamizono*

*   Add `ActiveRecord::Base.suppress` to prevent the receiver from being saved
    during the given block.

    For example, here's a pattern of creating notifications when new comments
    are posted. (The notification may in turn trigger an email, a push
    notification, or just appear in the UI somewhere):

        class Comment < ActiveRecord::Base
          belongs_to :commentable, polymorphic: true
          after_create -> { Notification.create! comment: self,
            recipients: commentable.recipients }
        end

    That's what you want the bulk of the time. A new comment creates a new
    Notification. There may be edge cases where you don't want that, like
    when copying a commentable and its comments, in which case write a
    concern with something like this:

        module Copyable
          def copy_to(destination)
            Notification.suppress do
              # Copy logic that creates new comments that we do not want triggering
              # notifications.
            end
          end
        end

    *Michael Ryan*

*   `:time` option added for `#touch`.

    Fixes #18905.

    *Hyonjee Joo*

*   Deprecate passing of `start` value to `find_in_batches` and `find_each`
    in favour of `begin_at` value.

    *Vipul A M*

*   Add `foreign_key_exists?` method.

    *Tõnis Simo*

*   Use SQL COUNT and LIMIT 1 queries for `none?` and `one?` methods
    if no block or limit is given, instead of loading the entire
    collection into memory. This applies to relations (e.g. `User.all`)
    as well as associations (e.g. `account.users`)

        # Before:

        users.none?
        # SELECT "users".* FROM "users"

        users.one?
        # SELECT "users".* FROM "users"

        # After:

        users.none?
        # SELECT 1 AS one FROM "users" LIMIT 1

        users.one?
        # SELECT COUNT(*) FROM "users"

    *Eugene Gilburg*

*   Have `enum` perform type casting consistently with the rest of Active
    Record, such as `where`.

    *Sean Griffin*

*   `scoping` no longer pollutes the current scope of sibling classes when using
    STI.

    Fixes #18806.

    Example:

        StiOne.none.scoping do
          StiTwo.all
        end


    *Sean Griffin*

*   `remove_reference` with `foreign_key: true` removes the foreign key before
    removing the column. This fixes a bug where it was not possible to remove
    the column on MySQL.

    Fixes #18664.

    *Yves Senn*

*   `find_in_batches` now accepts an `:finish` parameter that complements the `:start`
     parameter to specify where to stop batch processing.

    *Vipul A M*

*   Fix a rounding problem for PostgreSQL timestamp columns.

    If a timestamp column has a precision specified, it needs to
    format according to that.

    *Ryuta Kamizono*

*   Respect the database default charset for `schema_migrations` table.

    The charset of `version` column in `schema_migrations` table depends
    on the database default charset and collation rather than the encoding
    of the connection.

    *Ryuta Kamizono*

*   Raise `ArgumentError` when passing `nil` or `false` to `Relation#merge`.

    These are not valid values to merge in a relation, so it should warn users
    early.

    *Rafael Mendonça França*

*   Use `SCHEMA` instead of `DB_STRUCTURE` for specifying a structure file.

    This makes the `db:structure` tasks consistent with `test:load_structure`.

    *Dieter Komendera*

*   Respect custom primary keys for associations when calling `Relation#where`

    Fixes #18813.

    *Sean Griffin*

*   Fix several edge cases which could result in a counter cache updating
    twice or not updating at all for `has_many` and `has_many :through`.

    Fixes #10865.

    *Sean Griffin*

*   Foreign keys added by migrations were given random, generated names. This
    meant a different `structure.sql` would be generated every time a developer
    ran migrations on their machine.

    The generated part of foreign key names is now a hash of the table name and
    column name, which is consistent every time you run the migration.

    *Chris Sinjakli*

*   Validation errors would be raised for parent records when an association
    was saved when the parent had `validate: false`. It should not be the
    responsibility of the model to validate an associated object unless the
    object was created or modified by the parent.

    This fixes the issue by skipping validations if the parent record is
    persisted, not changed, and not marked for destruction.

    Fixes #17621.

    *Eileen M. Uchitelle*, *Aaron Patterson*

*   Fix n+1 query problem when eager loading nil associations (fixes #18312)

    *Sammy Larbi*

*   Change the default error message from `can't be blank` to `must exist` for
    the presence validator of the `:required` option on `belongs_to`/`has_one`
    associations.

    *Henrik Nygren*

*   Fixed `ActiveRecord::Relation#group` method when an argument is an SQL
    reserved keyword:

    Example:

        SplitTest.group(:key).count
        Property.group(:value).count

    *Bogdan Gusiev*

*   Added the `#or` method on `ActiveRecord::Relation`, allowing use of the OR
    operator to combine WHERE or HAVING clauses.

    Example:

        Post.where('id = 1').or(Post.where('id = 2'))
        # => SELECT * FROM posts WHERE (id = 1) OR (id = 2)

    *Sean Griffin*, *Matthew Draper*, *Gael Muller*, *Olivier El Mekki*

*   Don't define autosave association callbacks twice from
    `accepts_nested_attributes_for`.

    Fixes #18704.

    *Sean Griffin*

*   Integer types will no longer raise a `RangeError` when assigning an
    attribute, but will instead raise when going to the database.

    Fixes several vague issues which were never reported directly. See the
    commit message from the commit which added this line for some examples.

    *Sean Griffin*

*   Values which would error while being sent to the database (such as an
    ASCII-8BIT string with invalid UTF-8 bytes on SQLite3), no longer error on
    assignment. They will still error when sent to the database, but you are
    given the ability to re-assign it to a valid value.

    Fixes #18580.

    *Sean Griffin*

*   Don't remove join dependencies in `Relation#exists?`

    Fixes #18632.

    *Sean Griffin*

*   Invalid values assigned to a JSON column are assumed to be `nil`.

    Fixes #18629.

    *Sean Griffin*

*   Add `ActiveRecord::Base#accessed_fields`, which can be used to quickly
    discover which fields were read from a model when you are looking to only
    select the data you need from the database.

    *Sean Griffin*

*   Introduce the `:if_exists` option for `drop_table`.

    Example:

        drop_table(:posts, if_exists: true)

    That would execute:

        DROP TABLE IF EXISTS posts

    If the table doesn't exist, `if_exists: false` (the default) raises an
    exception whereas `if_exists: true` does nothing.

    *Cody Cutrer*, *Stefan Kanev*, *Ryuta Kamizono*

*   Don't run SQL if attribute value is not changed for update_attribute method.

    *Prathamesh Sonpatki*

*   `time` columns can now get affected by `time_zone_aware_attributes`. If you have
    set `config.time_zone` to a value other than `'UTC'`, they will be treated
    as in that time zone by default in Rails 5.1. If this is not the desired
    behavior, you can set

        ActiveRecord::Base.time_zone_aware_types = [:datetime]

    A deprecation warning will be emitted if you have a `:time` column, and have
    not explicitly opted out.

    Fixes #3145.

    *Sean Griffin*

*   Tests now run after_commit callbacks. You no longer have to declare
    `uses_transaction ‘test name’` to test the results of an after_commit.

    after_commit callbacks run after committing a transaction whose parent
    is not `joinable?`: un-nested transactions, transactions within test cases,
    and transactions in `console --sandbox`.

    *arthurnn*, *Ravil Bayramgalin*, *Matthew Draper*

*   `nil` as a value for a binary column in a query no longer logs as
    "<NULL binary data>", and instead logs as just "nil".

    *Sean Griffin*

*   `attribute_will_change!` will no longer cause non-persistable attributes to
    be sent to the database.

    Fixes #18407.

    *Sean Griffin*

*   Remove support for the `protected_attributes` gem.

    *Carlos Antonio da Silva*, *Roberto Miranda*

*   Fix accessing of fixtures having non-string labels like Fixnum.

    *Prathamesh Sonpatki*

*   Remove deprecated support to preload instance-dependent associations.

    *Yves Senn*

*   Remove deprecated support for PostgreSQL ranges with exclusive lower bounds.

    *Yves Senn*

*   Remove deprecation when modifying a relation with cached Arel.
    This raises an `ImmutableRelation` error instead.

    *Yves Senn*

*   Added `ActiveRecord::SecureToken` in order to encapsulate generation of
    unique tokens for attributes in a model using `SecureRandom`.

    *Roberto Miranda*

*   Change the behavior of boolean columns to be closer to Ruby's semantics.

    Before this change we had a small set of "truthy", and all others are "falsy".

    Now, we have a small set of "falsy" values and all others are "truthy" matching
    Ruby's semantics.

    *Rafael Mendonça França*

*   Deprecate `ActiveRecord::Base.errors_in_transactional_callbacks=`.

    *Rafael Mendonça França*

*   Change transaction callbacks to not swallow errors.

    Before this change any errors raised inside a transaction callback
    were getting rescued and printed in the logs.

    Now these errors are not rescued anymore and just bubble up, as the other callbacks.

    *Rafael Mendonça França*

*   Remove deprecated `sanitize_sql_hash_for_conditions`.

    *Rafael Mendonça França*

*   Remove deprecated `Reflection#source_macro`.

    *Rafael Mendonça França*

*   Remove deprecated `symbolized_base_class` and `symbolized_sti_name`.

    *Rafael Mendonça França*

*   Remove deprecated `ActiveRecord::Base.disable_implicit_join_references=`.

    *Rafael Mendonça França*

*   Remove deprecated access to connection specification using a string accessor.

    Now all strings will be handled as a URL.

    *Rafael Mendonça França*

*   Change the default `null` value for `timestamps` to `false`.

    *Rafael Mendonça França*

*   Return an array of pools from `connection_pools`.

    *Rafael Mendonça França*

*   Return a null column from `column_for_attribute` when no column exists.

    *Rafael Mendonça França*

*   Remove deprecated `serialized_attributes`.

    *Rafael Mendonça França*

*   Remove deprecated automatic counter caches on `has_many :through`.

    *Rafael Mendonça França*

*   Change the way in which callback chains can be halted.

    The preferred method to halt a callback chain from now on is to explicitly
    `throw(:abort)`.
    In the past, returning `false` in an Active Record `before_` callback had the
    side effect of halting the callback chain.
    This is not recommended anymore and, depending on the value of the
    `ActiveSupport.halt_callback_chains_on_return_false` option, will
    either not work at all or display a deprecation warning.

    *claudiob*

*   Clear query cache on rollback.

    *Florian Weingarten*

*   Fix setting of foreign_key for through associations when building a new record.

    Fixes #12698.

    *Ivan Antropov*

*   Improve dumping of the primary key. If it is not a default primary key,
    correctly dump the type and options.

    Fixes #14169, #16599.

    *Ryuta Kamizono*

*   Format the datetime string according to the precision of the datetime field.

    Incompatible to rounding behavior between MySQL 5.6 and earlier.

    In 5.5, when you insert `2014-08-17 12:30:00.999999` the fractional part
    is ignored. In 5.6, it's rounded to `2014-08-17 12:30:01`:

    http://bugs.mysql.com/bug.php?id=68760

    *Ryuta Kamizono*

*   Allow a precision option for MySQL datetimes.

    *Ryuta Kamizono*

*   Fixed automatic `inverse_of` for models nested in a module.

    *Andrew McCloud*

*   Change `ActiveRecord::Relation#update` behavior so that it can
    be called without passing ids of the records to be updated.

    This change allows updating multiple records returned by
    `ActiveRecord::Relation` with callbacks and validations.

        # Before
        # ArgumentError: wrong number of arguments (1 for 2)
        Comment.where(group: 'expert').update(body: "Group of Rails Experts")

        # After
        # Comments with group expert updated with body "Group of Rails Experts"
        Comment.where(group: 'expert').update(body: "Group of Rails Experts")

    *Prathamesh Sonpatki*

*   Fix `reaping_frequency` option when the value is a string.

    This usually happens when it is configured using `DATABASE_URL`.

    *korbin*

*   Fix error message when trying to create an associated record and the foreign
    key is missing.

    Before this fix the following exception was being raised:

        NoMethodError: undefined method `val' for #<Arel::Nodes::BindParam:0x007fc64d19c218>

    Now the message is:

        ActiveRecord::UnknownAttributeError: unknown attribute 'foreign_key' for Model.

    *Rafael Mendonça França*

*   Fix change detection problem for PostgreSQL bytea type and
    `ArgumentError: string contains null byte` exception with pg-0.18.

    Fixes #17680.

    *Lars Kanis*

*   When a table has a composite primary key, the `primary_key` method for
    SQLite3 and PostgreSQL adapters was only returning the first field of the key.
    Ensures that it will return nil instead, as Active Record doesn't support
    composite primary keys.

    Fixes #18070.

    *arthurnn*

*   `validates_size_of` / `validates_length_of` do not count records
    which are `marked_for_destruction?`.

    Fixes #7247.

    *Yves Senn*

*   Ensure `first!` and friends work on loaded associations.

    Fixes #18237.

    *Sean Griffin*

*   `eager_load` preserves readonly flag for associations.

    Fixes #15853.

    *Takashi Kokubun*

*   Provide `:touch` option to `save()` to accommodate saving without updating
    timestamps.

    Fixes #18202.

    *Dan Olson*

*   Provide a more helpful error message when an unsupported class is passed to
    `serialize`.

    Fixes #18224.

    *Sean Griffin*

*   Add bigint primary key support for MySQL.

    Example:

        create_table :foos, id: :bigint do |t|
        end

    *Ryuta Kamizono*

*   Support for any type of primary key.

    Fixes #14194.

    *Ryuta Kamizono*

*   Dump the default `nil` for PostgreSQL UUID primary key.

    *Ryuta Kamizono*

*   Add a `:foreign_key` option to `references` and associated migration
    methods. The model and migration generators now use this option, rather than
    the `add_foreign_key` form.

    *Sean Griffin*

*   Don't raise when writing an attribute with an out-of-range datetime passed
    by the user.

    *Grey Baker*

*   Replace deprecated `ActiveRecord::Tasks::DatabaseTasks#load_schema` with
    `ActiveRecord::Tasks::DatabaseTasks#load_schema_for`.

    *Yves Senn*

*   Fix bug with `ActiveRecord::Type::Numeric` that caused negative values to
    be marked as having changed when set to the same negative value.

    Fixes #18161.

    *Daniel Fox*

*   Introduce `force: :cascade` option for `create_table`. Using this option
    will recreate tables even if they have dependent objects (like foreign keys).
    `db/schema.rb` now uses `force: :cascade`. This makes it possible to
    reload the schema when foreign keys are in place.

    *Matthew Draper*, *Yves Senn*

*   `db:schema:load` and `db:structure:load` no longer purge the database
    before loading the schema. This is left for the user to do.
    `db:test:prepare` will still purge the database.

    Fixes #17945.

    *Yves Senn*

*   Fix undesirable RangeError by `Type::Integer`. Add `Type::UnsignedInteger`.

    *Ryuta Kamizono*

*   Add `foreign_type` option to `has_one` and `has_many` association macros.

    This option enables to define the column name of associated object's type for polymorphic associations.

    *Ulisses Almeida*, *Kassio Borges*

*   Remove deprecated behavior allowing nested arrays to be passed as query
    values.

    *Melanie Gilman*

*   Deprecate passing a class as a value in a query. Users should pass strings
    instead.

    *Melanie Gilman*

*   `add_timestamps` and `remove_timestamps` now properly reversible with
    options.

    *Noam Gagliardi-Rabinovich*

*   `ActiveRecord::ConnectionAdapters::ColumnDumper#column_spec` and
    `ActiveRecord::ConnectionAdapters::ColumnDumper#prepare_column_options` no
    longer have a `types` argument. They should access
    `connection#native_database_types` directly.

    *Yves Senn*

Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/activerecord/CHANGELOG.md) for previous changes.