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
|
# orm/events.py
# Copyright (C) 2005-2011 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""ORM event interfaces.
"""
from sqlalchemy import event, exc
import inspect
class InstrumentationEvents(event.Events):
"""Events related to class instrumentation events.
The listeners here support being established against
any new style class, that is any object that is a subclass
of 'type'. Events will then be fired off for events
against that class as well as all subclasses.
'type' itself is also accepted as a target
in which case the events fire for all classes.
"""
@classmethod
def _accept_with(cls, target):
from sqlalchemy.orm.instrumentation import instrumentation_registry
if isinstance(target, type):
return instrumentation_registry
else:
return None
@classmethod
def _listen(cls, target, identifier, fn, propagate=False):
event.Events._listen(target, identifier, fn, propagate=propagate)
@classmethod
def _remove(cls, identifier, target, fn):
raise NotImplementedError("Removal of instrumentation events not yet implemented")
def class_instrument(self, cls):
"""Called after the given class is instrumented.
To get at the :class:`.ClassManager`, use
:func:`.manager_of_class`.
"""
def class_uninstrument(self, cls):
"""Called before the given class is uninstrumented.
To get at the :class:`.ClassManager`, use
:func:`.manager_of_class`.
"""
def attribute_instrument(self, cls, key, inst):
"""Called when an attribute is instrumented."""
class InstanceEvents(event.Events):
"""Define events specific to object lifecycle.
e.g.::
from sqlalchemy import event
def my_load_listener(target, context):
print "on load!"
event.listen(SomeMappedClass, 'load', my_load_listener)
Available targets include mapped classes, instances of
:class:`.Mapper` (i.e. returned by :func:`.mapper`,
:func:`.class_mapper` and similar), as well as the
:class:`.Mapper` class and :func:`.mapper` function itself
for global event reception::
from sqlalchemy.orm import mapper
def some_listener(target, context):
log.debug("Instance %s being loaded" % target)
# attach to all mappers
event.listen(mapper, 'load', some_listener)
Instance events are closely related to mapper events, but
are more specific to the instance and its instrumentation,
rather than its system of persistence.
When using :class:`.InstanceEvents`, several modifiers are
available to the :func:`.event.listen` function.
:param propagate=False: When True, the event listener should
be applied to all inheriting mappers as well as the
mapper which is the target of this listener.
:param raw=False: When True, the "target" argument passed
to applicable event listener functions will be the
instance's :class:`.InstanceState` management
object, rather than the mapped instance itself.
"""
@classmethod
def _accept_with(cls, target):
from sqlalchemy.orm.instrumentation import ClassManager, manager_of_class
from sqlalchemy.orm import Mapper, mapper
if isinstance(target, ClassManager):
return target
elif isinstance(target, Mapper):
return target.class_manager
elif target is mapper:
return ClassManager
elif isinstance(target, type):
if issubclass(target, Mapper):
return ClassManager
else:
manager = manager_of_class(target)
if manager:
return manager
return None
@classmethod
def _listen(cls, target, identifier, fn, raw=False, propagate=False):
if not raw:
orig_fn = fn
def wrap(state, *arg, **kw):
return orig_fn(state.obj(), *arg, **kw)
fn = wrap
event.Events._listen(target, identifier, fn, propagate=propagate)
if propagate:
for mgr in target.subclass_managers(True):
event.Events._listen(mgr, identifier, fn, True)
@classmethod
def _remove(cls, identifier, target, fn):
raise NotImplementedError("Removal of instance events not yet implemented")
def first_init(self, manager, cls):
"""Called when the first instance of a particular mapping is called.
"""
def init(self, target, args, kwargs):
"""Receive an instance when it's constructor is called.
This method is only called during a userland construction of
an object. It is not called when an object is loaded from the
database.
"""
def init_failure(self, target, args, kwargs):
"""Receive an instance when it's constructor has been called,
and raised an exception.
This method is only called during a userland construction of
an object. It is not called when an object is loaded from the
database.
"""
def load(self, target, context):
"""Receive an object instance after it has been created via
``__new__``, and after initial attribute population has
occurred.
This typically occurs when the instance is created based on
incoming result rows, and is only called once for that
instance's lifetime.
Note that during a result-row load, this method is called upon
the first row received for this instance. Note that some
attributes and collections may or may not be loaded or even
initialized, depending on what's present in the result rows.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:param context: the :class:`.QueryContext` corresponding to the
current :class:`.Query` in progress. This argument may be
``None`` if the load does not correspond to a :class:`.Query`,
such as during :meth:`.Session.merge`.
"""
def refresh(self, target, context, attrs):
"""Receive an object instance after one or more attributes have
been refreshed from a query.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:param context: the :class:`.QueryContext` corresponding to the
current :class:`.Query` in progress.
:param attrs: iterable collection of attribute names which
were populated, or None if all column-mapped, non-deferred
attributes were populated.
"""
def expire(self, target, attrs):
"""Receive an object instance after its attributes or some subset
have been expired.
'keys' is a list of attribute names. If None, the entire
state was expired.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:param attrs: iterable collection of attribute
names which were expired, or None if all attributes were
expired.
"""
def resurrect(self, target):
"""Receive an object instance as it is 'resurrected' from
garbage collection, which occurs when a "dirty" state falls
out of scope.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
"""
def pickle(self, target, state_dict):
"""Receive an object instance when its associated state is
being pickled.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:param state_dict: the dictionary returned by
:class:`.InstanceState.__getstate__`, containing the state
to be pickled.
"""
def unpickle(self, target, state_dict):
"""Receive an object instance after it's associated state has
been unpickled.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:param state_dict: the dictionary sent to
:class:`.InstanceState.__setstate__`, containing the state
dictionary which was pickled.
"""
class MapperEvents(event.Events):
"""Define events specific to mappings.
e.g.::
from sqlalchemy import event
def my_before_insert_listener(mapper, connection, target):
# execute a stored procedure upon INSERT,
# apply the value to the row to be inserted
target.calculated_value = connection.scalar(
"select my_special_function(%d)"
% target.special_number)
# associate the listener function with SomeMappedClass,
# to execute during the "before_insert" hook
event.listen(SomeMappedClass, 'before_insert', my_before_insert_listener)
Available targets include mapped classes, instances of
:class:`.Mapper` (i.e. returned by :func:`.mapper`,
:func:`.class_mapper` and similar), as well as the
:class:`.Mapper` class and :func:`.mapper` function itself
for global event reception::
from sqlalchemy.orm import mapper
def some_listener(mapper, connection, target):
log.debug("Instance %s being inserted" % target)
# attach to all mappers
event.listen(mapper, 'before_insert', some_listener)
Mapper events provide hooks into critical sections of the
mapper, including those related to object instrumentation,
object loading, and object persistence. In particular, the
persistence methods :meth:`~.MapperEvents.before_insert`,
and :meth:`~.MapperEvents.before_update` are popular
places to augment the state being persisted - however, these
methods operate with several significant restrictions. The
user is encouraged to evaluate the
:meth:`.SessionEvents.before_flush` and
:meth:`.SessionEvents.after_flush` methods as more
flexible and user-friendly hooks in which to apply
additional database state during a flush.
When using :class:`.MapperEvents`, several modifiers are
available to the :func:`.event.listen` function.
:param propagate=False: When True, the event listener should
be applied to all inheriting mappers as well as the
mapper which is the target of this listener.
:param raw=False: When True, the "target" argument passed
to applicable event listener functions will be the
instance's :class:`.InstanceState` management
object, rather than the mapped instance itself.
:param retval=False: when True, the user-defined event function
must have a return value, the purpose of which is either to
control subsequent event propagation, or to otherwise alter
the operation in progress by the mapper. Possible return
values are:
* ``sqlalchemy.orm.interfaces.EXT_CONTINUE`` - continue event
processing normally.
* ``sqlalchemy.orm.interfaces.EXT_STOP`` - cancel all subsequent
event handlers in the chain.
* other values - the return value specified by specific listeners,
such as :meth:`~.MapperEvents.translate_row` or
:meth:`~.MapperEvents.create_instance`.
"""
@classmethod
def _accept_with(cls, target):
from sqlalchemy.orm import mapper, class_mapper, Mapper
if target is mapper:
return Mapper
elif isinstance(target, type):
if issubclass(target, Mapper):
return target
else:
return class_mapper(target)
else:
return target
@classmethod
def _listen(cls, target, identifier, fn,
raw=False, retval=False, propagate=False):
from sqlalchemy.orm.interfaces import EXT_CONTINUE
if not raw or not retval:
if not raw:
meth = getattr(cls, identifier)
try:
target_index = inspect.getargspec(meth)[0].index('target') - 1
except ValueError:
target_index = None
wrapped_fn = fn
def wrap(*arg, **kw):
if not raw and target_index is not None:
arg = list(arg)
arg[target_index] = arg[target_index].obj()
if not retval:
wrapped_fn(*arg, **kw)
return EXT_CONTINUE
else:
return wrapped_fn(*arg, **kw)
fn = wrap
if propagate:
for mapper in target.self_and_descendants:
event.Events._listen(mapper, identifier, fn, propagate=True)
else:
event.Events._listen(target, identifier, fn)
def instrument_class(self, mapper, class_):
"""Receive a class when the mapper is first constructed,
before instrumentation is applied to the mapped class.
This event is the earliest phase of mapper construction.
Most attributes of the mapper are not yet initialized.
This listener can generally only be applied to the :class:`.Mapper`
class overall.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param class\_: the mapped class.
"""
def mapper_configured(self, mapper, class_):
"""Called when the mapper for the class is fully configured.
This event is the latest phase of mapper construction.
The mapper should be in its final state.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param class\_: the mapped class.
"""
# TODO: need coverage for this event
def translate_row(self, mapper, context, row):
"""Perform pre-processing on the given result row and return a
new row instance.
This listener is typically registered with ``retval=True``.
It is called when the mapper first receives a row, before
the object identity or the instance itself has been derived
from that row. The given row may or may not be a
:class:`.RowProxy` object - it will always be a dictionary-like
object which contains mapped columns as keys. The
returned object should also be a dictionary-like object
which recognizes mapped columns as keys.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param context: the :class:`.QueryContext`, which includes
a handle to the current :class:`.Query` in progress as well
as additional state information.
:param row: the result row being handled. This may be
an actual :class:`.RowProxy` or may be a dictionary containing
:class:`.Column` objects as keys.
:return: When configured with ``retval=True``, the function
should return a dictionary-like row object, or ``EXT_CONTINUE``,
indicating the original row should be used.
"""
def create_instance(self, mapper, context, row, class_):
"""Receive a row when a new object instance is about to be
created from that row.
The method can choose to create the instance itself, or it can return
EXT_CONTINUE to indicate normal object creation should take place.
This listener is typically registered with ``retval=True``.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param context: the :class:`.QueryContext`, which includes
a handle to the current :class:`.Query` in progress as well
as additional state information.
:param row: the result row being handled. This may be
an actual :class:`.RowProxy` or may be a dictionary containing
:class:`.Column` objects as keys.
:param class\_: the mapped class.
:return: When configured with ``retval=True``, the return value
should be a newly created instance of the mapped class,
or ``EXT_CONTINUE`` indicating that default object construction
should take place.
"""
def append_result(self, mapper, context, row, target,
result, **flags):
"""Receive an object instance before that instance is appended
to a result list.
This is a rarely used hook which can be used to alter
the construction of a result list returned by :class:`.Query`.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param context: the :class:`.QueryContext`, which includes
a handle to the current :class:`.Query` in progress as well
as additional state information.
:param row: the result row being handled. This may be
an actual :class:`.RowProxy` or may be a dictionary containing
:class:`.Column` objects as keys.
:param target: the mapped instance being populated. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:param result: a list-like object where results are being
appended.
:param \**flags: Additional state information about the
current handling of the row.
:return: If this method is registered with ``retval=True``,
a return value of ``EXT_STOP`` will prevent the instance
from being appended to the given result list, whereas a
return value of ``EXT_CONTINUE`` will result in the default
behavior of appending the value to the result list.
"""
def populate_instance(self, mapper, context, row,
target, **flags):
"""Receive an instance before that instance has
its attributes populated.
This usually corresponds to a newly loaded instance but may
also correspond to an already-loaded instance which has
unloaded attributes to be populated. The method may be called
many times for a single instance, as multiple result rows are
used to populate eagerly loaded collections.
Most usages of this hook are obsolete. For a
generic "object has been newly created from a row" hook, use
:meth:`.InstanceEvents.load`.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param context: the :class:`.QueryContext`, which includes
a handle to the current :class:`.Query` in progress as well
as additional state information.
:param row: the result row being handled. This may be
an actual :class:`.RowProxy` or may be a dictionary containing
:class:`.Column` objects as keys.
:param target: the mapped instance. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: When configured with ``retval=True``, a return
value of ``EXT_STOP`` will bypass instance population by
the mapper. A value of ``EXT_CONTINUE`` indicates that
default instance population should take place.
"""
def before_insert(self, mapper, connection, target):
"""Receive an object instance before an INSERT statement
is emitted corresponding to that instance.
This event is used to modify local, non-object related
attributes on the instance before an INSERT occurs, as well
as to emit additional SQL statements on the given
connection.
The event is often called for a batch of objects of the
same class before their INSERT statements are emitted at
once in a later step. In the extremely rare case that
this is not desirable, the :func:`.mapper` can be
configured with ``batch=False``, which will cause
batches of instances to be broken up into individual
(and more poorly performing) event->persist->event
steps.
Handlers should **not** modify any attributes which are
mapped by :func:`.relationship`, nor should they attempt
to make any modifications to the :class:`.Session` in
this hook (including :meth:`.Session.add`,
:meth:`.Session.delete`, etc.) - such changes will not
take effect. For overall changes to the "flush plan",
use :meth:`.SessionEvents.before_flush`.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param connection: the :class:`.Connection` being used to
emit INSERT statements for this instance. This
provides a handle into the current transaction on the
target database specific to this instance.
:param target: the mapped instance being persisted. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: No return value is supported by this event.
"""
def after_insert(self, mapper, connection, target):
"""Receive an object instance after an INSERT statement
is emitted corresponding to that instance.
This event is used to modify in-Python-only
state on the instance after an INSERT occurs, as well
as to emit additional SQL statements on the given
connection.
The event is often called for a batch of objects of the
same class after their INSERT statements have been
emitted at once in a previous step. In the extremely
rare case that this is not desirable, the
:func:`.mapper` can be configured with ``batch=False``,
which will cause batches of instances to be broken up
into individual (and more poorly performing)
event->persist->event steps.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param connection: the :class:`.Connection` being used to
emit INSERT statements for this instance. This
provides a handle into the current transaction on the
target database specific to this instance.
:param target: the mapped instance being persisted. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: No return value is supported by this event.
"""
def before_update(self, mapper, connection, target):
"""Receive an object instance before an UPDATE statement
is emitted corresponding to that instance.
This event is used to modify local, non-object related
attributes on the instance before an UPDATE occurs, as well
as to emit additional SQL statements on the given
connection.
This method is called for all instances that are
marked as "dirty", *even those which have no net changes
to their column-based attributes*. An object is marked
as dirty when any of its column-based attributes have a
"set attribute" operation called or when any of its
collections are modified. If, at update time, no
column-based attributes have any net changes, no UPDATE
statement will be issued. This means that an instance
being sent to :meth:`~.MapperEvents.before_update` is
*not* a guarantee that an UPDATE statement will be
issued, although you can affect the outcome here by
modifying attributes so that a net change in value does
exist.
To detect if the column-based attributes on the object have net
changes, and will therefore generate an UPDATE statement, use
``object_session(instance).is_modified(instance,
include_collections=False)``.
The event is often called for a batch of objects of the
same class before their UPDATE statements are emitted at
once in a later step. In the extremely rare case that
this is not desirable, the :func:`.mapper` can be
configured with ``batch=False``, which will cause
batches of instances to be broken up into individual
(and more poorly performing) event->persist->event
steps.
Handlers should **not** modify any attributes which are
mapped by :func:`.relationship`, nor should they attempt
to make any modifications to the :class:`.Session` in
this hook (including :meth:`.Session.add`,
:meth:`.Session.delete`, etc.) - such changes will not
take effect. For overall changes to the "flush plan",
use :meth:`.SessionEvents.before_flush`.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param connection: the :class:`.Connection` being used to
emit UPDATE statements for this instance. This
provides a handle into the current transaction on the
target database specific to this instance.
:param target: the mapped instance being persisted. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: No return value is supported by this event.
"""
def after_update(self, mapper, connection, target):
"""Receive an object instance after an UPDATE statement
is emitted corresponding to that instance.
This event is used to modify in-Python-only
state on the instance after an UPDATE occurs, as well
as to emit additional SQL statements on the given
connection.
This method is called for all instances that are
marked as "dirty", *even those which have no net changes
to their column-based attributes*, and for which
no UPDATE statement has proceeded. An object is marked
as dirty when any of its column-based attributes have a
"set attribute" operation called or when any of its
collections are modified. If, at update time, no
column-based attributes have any net changes, no UPDATE
statement will be issued. This means that an instance
being sent to :meth:`~.MapperEvents.after_update` is
*not* a guarantee that an UPDATE statement has been
issued.
To detect if the column-based attributes on the object have net
changes, and therefore resulted in an UPDATE statement, use
``object_session(instance).is_modified(instance,
include_collections=False)``.
The event is often called for a batch of objects of the
same class after their UPDATE statements have been emitted at
once in a previous step. In the extremely rare case that
this is not desirable, the :func:`.mapper` can be
configured with ``batch=False``, which will cause
batches of instances to be broken up into individual
(and more poorly performing) event->persist->event
steps.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param connection: the :class:`.Connection` being used to
emit UPDATE statements for this instance. This
provides a handle into the current transaction on the
target database specific to this instance.
:param target: the mapped instance being persisted. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: No return value is supported by this event.
"""
def before_delete(self, mapper, connection, target):
"""Receive an object instance before a DELETE statement
is emitted corresponding to that instance.
This event is used to emit additional SQL statements on
the given connection as well as to perform application
specific bookkeeping related to a deletion event.
The event is often called for a batch of objects of the
same class before their DELETE statements are emitted at
once in a later step.
Handlers should **not** modify any attributes which are
mapped by :func:`.relationship`, nor should they attempt
to make any modifications to the :class:`.Session` in
this hook (including :meth:`.Session.add`,
:meth:`.Session.delete`, etc.) - such changes will not
take effect. For overall changes to the "flush plan",
use :meth:`.SessionEvents.before_flush`.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param connection: the :class:`.Connection` being used to
emit DELETE statements for this instance. This
provides a handle into the current transaction on the
target database specific to this instance.
:param target: the mapped instance being deleted. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: No return value is supported by this event.
"""
def after_delete(self, mapper, connection, target):
"""Receive an object instance after a DELETE statement
has been emitted corresponding to that instance.
This event is used to emit additional SQL statements on
the given connection as well as to perform application
specific bookkeeping related to a deletion event.
The event is often called for a batch of objects of the
same class after their DELETE statements have been emitted at
once in a previous step.
:param mapper: the :class:`.Mapper` which is the target
of this event.
:param connection: the :class:`.Connection` being used to
emit DELETE statements for this instance. This
provides a handle into the current transaction on the
target database specific to this instance.
:param target: the mapped instance being deleted. If
the event is configured with ``raw=True``, this will
instead be the :class:`.InstanceState` state-management
object associated with the instance.
:return: No return value is supported by this event.
"""
@classmethod
def _remove(cls, identifier, target, fn):
raise NotImplementedError("Removal of mapper events not yet implemented")
class SessionEvents(event.Events):
"""Define events specific to :class:`.Session` lifecycle.
e.g.::
from sqlalchemy import event
from sqlalchemy.orm import sessionmaker
def my_before_commit(session):
print "before commit!"
Session = sessionmaker()
event.listen(Session, "before_commit", my_before_commit)
The :func:`~.event.listen` function will accept
:class:`.Session` objects as well as the return result
of :func:`.sessionmaker` and :func:`.scoped_session`.
Additionally, it accepts the :class:`.Session` class which
will apply listeners to all :class:`.Session` instances
globally.
"""
@classmethod
def _accept_with(cls, target):
from sqlalchemy.orm import ScopedSession, Session
if isinstance(target, ScopedSession):
if not isinstance(target.session_factory, type) or \
not issubclass(target.session_factory, Session):
raise exc.ArgumentError(
"Session event listen on a ScopedSession "
"requires that its creation callable "
"is a Session subclass.")
return target.session_factory
elif isinstance(target, type):
if issubclass(target, ScopedSession):
return Session
elif issubclass(target, Session):
return target
elif isinstance(target, Session):
return target
else:
return None
@classmethod
def _remove(cls, identifier, target, fn):
raise NotImplementedError("Removal of session events not yet implemented")
def before_commit(self, session):
"""Execute before commit is called.
Note that this may not be per-flush if a longer running
transaction is ongoing."""
def after_commit(self, session):
"""Execute after a commit has occurred.
Note that this may not be per-flush if a longer running
transaction is ongoing."""
def after_rollback(self, session):
"""Execute after a rollback has occurred.
Note that this may not be per-flush if a longer running
transaction is ongoing."""
def before_flush( self, session, flush_context, instances):
"""Execute before flush process has started.
`instances` is an optional list of objects which were passed to
the ``flush()`` method. """
def after_flush(self, session, flush_context):
"""Execute after flush has completed, but before commit has been
called.
Note that the session's state is still in pre-flush, i.e. 'new',
'dirty', and 'deleted' lists still show pre-flush state as well
as the history settings on instance attributes."""
def after_flush_postexec(self, session, flush_context):
"""Execute after flush has completed, and after the post-exec
state occurs.
This will be when the 'new', 'dirty', and 'deleted' lists are in
their final state. An actual commit() may or may not have
occurred, depending on whether or not the flush started its own
transaction or participated in a larger transaction. """
def after_begin( self, session, transaction, connection):
"""Execute after a transaction is begun on a connection
`transaction` is the SessionTransaction. This method is called
after an engine level transaction is begun on a connection. """
def after_attach(self, session, instance):
"""Execute after an instance is attached to a session.
This is called after an add, delete or merge. """
def after_bulk_update( self, session, query, query_context, result):
"""Execute after a bulk update operation to the session.
This is called after a session.query(...).update()
`query` is the query object that this update operation was
called on. `query_context` was the query context object.
`result` is the result object returned from the bulk operation.
"""
def after_bulk_delete( self, session, query, query_context, result):
"""Execute after a bulk delete operation to the session.
This is called after a session.query(...).delete()
`query` is the query object that this delete operation was
called on. `query_context` was the query context object.
`result` is the result object returned from the bulk operation.
"""
class AttributeEvents(event.Events):
"""Define events for object attributes.
These are typically defined on the class-bound descriptor for the
target class.
e.g.::
from sqlalchemy import event
def my_append_listener(target, value, initiator):
print "received append event for target: %s" % target
event.listen(MyClass.collection, 'append', my_append_listener)
Listeners have the option to return a possibly modified version
of the value, when the ``retval=True`` flag is passed
to :func:`~.event.listen`::
def validate_phone(target, value, oldvalue, initiator):
"Strip non-numeric characters from a phone number"
return re.sub(r'(?![0-9])', '', value)
# setup listener on UserContact.phone attribute, instructing
# it to use the return value
listen(UserContact.phone, 'set', validate_phone, retval=True)
A validation function like the above can also raise an exception
such as :class:`.ValueError` to halt the operation.
Several modifiers are available to the :func:`~.event.listen` function.
:param active_history=False: When True, indicates that the
"set" event would like to receive the "old" value being
replaced unconditionally, even if this requires firing off
database loads. Note that ``active_history`` can also be
set directly via :func:`.column_property` and
:func:`.relationship`.
:param propagate=False: When True, the listener function will
be established not just for the class attribute given, but
for attributes of the same name on all current subclasses
of that class, as well as all future subclasses of that
class, using an additional listener that listens for
instrumentation events.
:param raw=False: When True, the "target" argument to the
event will be the :class:`.InstanceState` management
object, rather than the mapped instance itself.
:param retval=False: when True, the user-defined event
listening must return the "value" argument from the
function. This gives the listening function the opportunity
to change the value that is ultimately used for a "set"
or "append" event.
"""
@classmethod
def _accept_with(cls, target):
from sqlalchemy.orm import interfaces
# TODO: coverage
if isinstance(target, interfaces.MapperProperty):
return getattr(target.parent.class_, target.key)
else:
return target
@classmethod
def _listen(cls, target, identifier, fn, active_history=False,
raw=False, retval=False,
propagate=False):
if active_history:
target.dispatch._active_history = True
# TODO: for removal, need to package the identity
# of the wrapper with the original function.
if not raw or not retval:
orig_fn = fn
def wrap(target, value, *arg):
if not raw:
target = target.obj()
if not retval:
orig_fn(target, value, *arg)
return value
else:
return orig_fn(target, value, *arg)
fn = wrap
event.Events._listen(target, identifier, fn, propagate)
if propagate:
from sqlalchemy.orm.instrumentation import manager_of_class
manager = manager_of_class(target.class_)
for mgr in manager.subclass_managers(True):
event.Events._listen(mgr[target.key], identifier, fn, True)
@classmethod
def _remove(cls, identifier, target, fn):
raise NotImplementedError("Removal of attribute events not yet implemented")
def append(self, target, value, initiator):
"""Receive a collection append event.
:param target: the object instance receiving the event.
If the listener is registered with ``raw=True``, this will
be the :class:`.InstanceState` object.
:param value: the value being appended. If this listener
is registered with ``retval=True``, the listener
function must return this value, or a new value which
replaces it.
:param initiator: the attribute implementation object
which initiated this event.
:return: if the event was registered with ``retval=True``,
the given value, or a new effective value, should be returned.
"""
def remove(self, target, value, initiator):
"""Receive a collection remove event.
:param target: the object instance receiving the event.
If the listener is registered with ``raw=True``, this will
be the :class:`.InstanceState` object.
:param value: the value being removed.
:param initiator: the attribute implementation object
which initiated this event.
:return: No return value is defined for this event.
"""
def set(self, target, value, oldvalue, initiator):
"""Receive a scalar set event.
:param target: the object instance receiving the event.
If the listener is registered with ``raw=True``, this will
be the :class:`.InstanceState` object.
:param value: the value being set. If this listener
is registered with ``retval=True``, the listener
function must return this value, or a new value which
replaces it.
:param oldvalue: the previous value being replaced. This
may also be the symbol ``NEVER_SET`` or ``NO_VALUE``.
If the listener is registered with ``active_history=True``,
the previous value of the attribute will be loaded from
the database if the existing value is currently unloaded
or expired.
:param initiator: the attribute implementation object
which initiated this event.
:return: if the event was registered with ``retval=True``,
the given value, or a new effective value, should be returned.
"""
|