root / snf-django-lib / snf_django / lib / db / managers.py @ 0f66865f
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1 | ea1e5d9f | Giorgos Korfiatis | # Copyright 2012, 2013 GRNET S.A. All rights reserved.
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2 | ee45eb81 | Giorgos Korfiatis | #
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3 | ee45eb81 | Giorgos Korfiatis | # Redistribution and use in source and binary forms, with or without
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4 | ee45eb81 | Giorgos Korfiatis | # modification, are permitted provided that the following conditions
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5 | ee45eb81 | Giorgos Korfiatis | # are met:
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6 | ee45eb81 | Giorgos Korfiatis | #
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7 | ee45eb81 | Giorgos Korfiatis | # 1. Redistributions of source code must retain the above copyright
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8 | ee45eb81 | Giorgos Korfiatis | # notice, this list of conditions and the following disclaimer.
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9 | ee45eb81 | Giorgos Korfiatis | #
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10 | ee45eb81 | Giorgos Korfiatis | # 2. Redistributions in binary form must reproduce the above copyright
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11 | ee45eb81 | Giorgos Korfiatis | # notice, this list of conditions and the following disclaimer in the
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12 | ee45eb81 | Giorgos Korfiatis | # documentation and/or other materials provided with the distribution.
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13 | ee45eb81 | Giorgos Korfiatis | #
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14 | ee45eb81 | Giorgos Korfiatis | # THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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15 | ee45eb81 | Giorgos Korfiatis | # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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16 | ee45eb81 | Giorgos Korfiatis | # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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17 | ee45eb81 | Giorgos Korfiatis | # ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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18 | ee45eb81 | Giorgos Korfiatis | # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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19 | ee45eb81 | Giorgos Korfiatis | # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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20 | ee45eb81 | Giorgos Korfiatis | # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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21 | ee45eb81 | Giorgos Korfiatis | # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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22 | ee45eb81 | Giorgos Korfiatis | # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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23 | ee45eb81 | Giorgos Korfiatis | # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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24 | ee45eb81 | Giorgos Korfiatis | # SUCH DAMAGE.
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25 | ee45eb81 | Giorgos Korfiatis | #
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26 | ee45eb81 | Giorgos Korfiatis | # The views and conclusions contained in the software and documentation are
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27 | ee45eb81 | Giorgos Korfiatis | # those of the authors and should not be interpreted as representing official
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28 | ee45eb81 | Giorgos Korfiatis | # policies, either expressed or implied, of GRNET S.A.
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29 | ee45eb81 | Giorgos Korfiatis | |
30 | ee45eb81 | Giorgos Korfiatis | from django.db import connections |
31 | ee45eb81 | Giorgos Korfiatis | from django.db.models import Manager |
32 | 1fd14d3d | Giorgos Korfiatis | from django.db.models.query import QuerySet, EmptyQuerySet |
33 | 1fd14d3d | Giorgos Korfiatis | from django.db.models.sql.datastructures import EmptyResultSet |
34 | ee45eb81 | Giorgos Korfiatis | |
35 | ee45eb81 | Giorgos Korfiatis | class ForUpdateManager(Manager): |
36 | ee45eb81 | Giorgos Korfiatis | """ Model manager implementing SELECT .. FOR UPDATE statement
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37 | ee45eb81 | Giorgos Korfiatis |
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38 | ee45eb81 | Giorgos Korfiatis | This manager implements select_for_update() method in order to use
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39 | ee45eb81 | Giorgos Korfiatis | row-level locking in the database and guarantee exclusive access, since
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40 | ee45eb81 | Giorgos Korfiatis | this method is only implemented in Django>=1.4.
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41 | ee45eb81 | Giorgos Korfiatis |
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42 | ee45eb81 | Giorgos Korfiatis | Non-blocking reads are not implemented, and each query including a row
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43 | ee45eb81 | Giorgos Korfiatis | that is locked by another transaction will block until the lock is
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44 | ee45eb81 | Giorgos Korfiatis | released. Also care must be taken in order to avoid deadlocks or retry
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45 | ee45eb81 | Giorgos Korfiatis | transactions that abort due to deadlocks.
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46 | ee45eb81 | Giorgos Korfiatis |
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47 | ee45eb81 | Giorgos Korfiatis | Example:
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48 | ea1e5d9f | Giorgos Korfiatis | networks = Network.objects.filter(public=True).select_for_update()
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49 | ee45eb81 | Giorgos Korfiatis |
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50 | ee45eb81 | Giorgos Korfiatis | """
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51 | ee45eb81 | Giorgos Korfiatis | |
52 | ea1e5d9f | Giorgos Korfiatis | def get_query_set(self): |
53 | ea1e5d9f | Giorgos Korfiatis | return ForUpdateQuerySet(self.model, using=self._db) |
54 | ee45eb81 | Giorgos Korfiatis | |
55 | ea1e5d9f | Giorgos Korfiatis | def get_for_update(self, *args, **kwargs): |
56 | ea1e5d9f | Giorgos Korfiatis | query = for_update(self.filter(*args, **kwargs))
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57 | ee45eb81 | Giorgos Korfiatis | query = list(query)
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58 | ee45eb81 | Giorgos Korfiatis | num = len(query)
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59 | ee45eb81 | Giorgos Korfiatis | if num == 1: |
60 | ee45eb81 | Giorgos Korfiatis | return query[0] |
61 | ee45eb81 | Giorgos Korfiatis | if not num: |
62 | ee45eb81 | Giorgos Korfiatis | raise self.model.DoesNotExist( |
63 | ee45eb81 | Giorgos Korfiatis | "%s matching query does not exist. "
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64 | ee45eb81 | Giorgos Korfiatis | "Lookup parameters were %s" %
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65 | ee45eb81 | Giorgos Korfiatis | (self.model._meta.object_name, kwargs))
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66 | ee45eb81 | Giorgos Korfiatis | raise self.model.MultipleObjectsReturned( |
67 | ee45eb81 | Giorgos Korfiatis | "get() returned more than one %s -- it returned %s! "
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68 | ee45eb81 | Giorgos Korfiatis | "Lookup parameters were %s" %
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69 | ee45eb81 | Giorgos Korfiatis | (self.model._meta.object_name, num, kwargs))
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70 | ee45eb81 | Giorgos Korfiatis | |
71 | ea1e5d9f | Giorgos Korfiatis | |
72 | ea1e5d9f | Giorgos Korfiatis | class ForUpdateQuerySet(QuerySet): |
73 | ea1e5d9f | Giorgos Korfiatis | |
74 | ea1e5d9f | Giorgos Korfiatis | def select_for_update(self): |
75 | ea1e5d9f | Giorgos Korfiatis | return for_update(self) |
76 | ee45eb81 | Giorgos Korfiatis | |
77 | ee45eb81 | Giorgos Korfiatis | |
78 | ee45eb81 | Giorgos Korfiatis | def for_update(query): |
79 | ee45eb81 | Giorgos Korfiatis | """ Rewrite query using SELECT .. FOR UPDATE.
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80 | ee45eb81 | Giorgos Korfiatis |
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81 | ee45eb81 | Giorgos Korfiatis | """
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82 | ee45eb81 | Giorgos Korfiatis | if 'sqlite' in connections[query.db].settings_dict['ENGINE'].lower(): |
83 | ee45eb81 | Giorgos Korfiatis | # SQLite does not support FOR UPDATE
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84 | ee45eb81 | Giorgos Korfiatis | return query
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85 | 1fd14d3d | Giorgos Korfiatis | try:
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86 | 1fd14d3d | Giorgos Korfiatis | sql, params = query.query.get_compiler(query.db).as_sql() |
87 | 1fd14d3d | Giorgos Korfiatis | except EmptyResultSet:
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88 | 1fd14d3d | Giorgos Korfiatis | return EmptyQuerySet()
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89 | ee45eb81 | Giorgos Korfiatis | return query.model._default_manager.raw(sql.rstrip() + ' FOR UPDATE', |
90 | ee45eb81 | Giorgos Korfiatis | params) |