root / snf-cyclades-app / synnefo / db / managers.py @ bb8fb9af
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1 | dbecf586 | Christos Stavrakakis | # Copyright 2012, 2013 GRNET S.A. All rights reserved.
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2 | 864bed43 | Christos Stavrakakis | #
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3 | 864bed43 | Christos Stavrakakis | # Redistribution and use in source and binary forms, with or without
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4 | 864bed43 | Christos Stavrakakis | # modification, are permitted provided that the following conditions
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5 | 864bed43 | Christos Stavrakakis | # are met:
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6 | 864bed43 | Christos Stavrakakis | #
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7 | 864bed43 | Christos Stavrakakis | # 1. Redistributions of source code must retain the above copyright
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8 | 864bed43 | Christos Stavrakakis | # notice, this list of conditions and the following disclaimer.
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9 | 864bed43 | Christos Stavrakakis | #
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10 | 864bed43 | Christos Stavrakakis | # 2. Redistributions in binary form must reproduce the above copyright
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11 | 864bed43 | Christos Stavrakakis | # notice, this list of conditions and the following disclaimer in the
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12 | 864bed43 | Christos Stavrakakis | # documentation and/or other materials provided with the distribution.
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13 | 864bed43 | Christos Stavrakakis | #
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14 | 864bed43 | Christos Stavrakakis | # THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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15 | 864bed43 | Christos Stavrakakis | # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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16 | 864bed43 | Christos Stavrakakis | # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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17 | 864bed43 | Christos Stavrakakis | # ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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18 | 864bed43 | Christos Stavrakakis | # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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19 | 864bed43 | Christos Stavrakakis | # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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20 | 864bed43 | Christos Stavrakakis | # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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21 | 864bed43 | Christos Stavrakakis | # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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22 | 864bed43 | Christos Stavrakakis | # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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23 | 864bed43 | Christos Stavrakakis | # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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24 | 864bed43 | Christos Stavrakakis | # SUCH DAMAGE.
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25 | 864bed43 | Christos Stavrakakis | #
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26 | 864bed43 | Christos Stavrakakis | # The views and conclusions contained in the software and documentation are
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27 | 864bed43 | Christos Stavrakakis | # those of the authors and should not be interpreted as representing official
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28 | 864bed43 | Christos Stavrakakis | # policies, either expressed or implied, of GRNET S.A.
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29 | 864bed43 | Christos Stavrakakis | |
30 | 864bed43 | Christos Stavrakakis | from django.db import connections |
31 | 864bed43 | Christos Stavrakakis | from django.db.models import Manager |
32 | 864bed43 | Christos Stavrakakis | from django.db.models.query import QuerySet |
33 | 864bed43 | Christos Stavrakakis | |
34 | 864bed43 | Christos Stavrakakis | |
35 | 864bed43 | Christos Stavrakakis | class ForUpdateManager(Manager): |
36 | dbecf586 | Christos Stavrakakis | """Model manager implementing SELECT .. FOR UPDATE statement
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37 | 864bed43 | Christos Stavrakakis |
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38 | dbecf586 | Christos Stavrakakis | This manager implements select_for_update() method in order to use
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39 | dbecf586 | Christos Stavrakakis | row-level locking in the database and guarantee exclusive access, since
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40 | dbecf586 | Christos Stavrakakis | this method is only implemented in Django>=1.4.
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41 | 864bed43 | Christos Stavrakakis |
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42 | dbecf586 | Christos Stavrakakis | Non-blocking reads are not implemented, and each query including a row
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43 | dbecf586 | Christos Stavrakakis | that is locked by another transaction will block until the lock is
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44 | dbecf586 | Christos Stavrakakis | released. Also care must be taken in order to avoid deadlocks or retry
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45 | dbecf586 | Christos Stavrakakis | transactions that abort due to deadlocks.
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46 | 864bed43 | Christos Stavrakakis |
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47 | dbecf586 | Christos Stavrakakis | Example:
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48 | dbecf586 | Christos Stavrakakis | networks = Network.objects.select_for_update().filter(public=True)
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49 | 864bed43 | Christos Stavrakakis |
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50 | 864bed43 | Christos Stavrakakis | """
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51 | 864bed43 | Christos Stavrakakis | |
52 | 1c11bace | Christos Stavrakakis | def select_for_update(self, *args, **kwargs): |
53 | 1c11bace | Christos Stavrakakis | return ForUpdateQuerySet(self.model, using=self.db) |
54 | 1c11bace | Christos Stavrakakis | |
55 | 1c11bace | Christos Stavrakakis | |
56 | 1c11bace | Christos Stavrakakis | class ForUpdateQuerySet(QuerySet): |
57 | dbecf586 | Christos Stavrakakis | """QuerySet implmenting SELECT .. FOR UPDATE statement
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58 | 1c11bace | Christos Stavrakakis |
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59 | 1c11bace | Christos Stavrakakis | This QuerySet overrides filter and get methods in order to implement
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60 | 1c11bace | Christos Stavrakakis | select_for_update() statement, by appending 'FOR UPDATE' to the end
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61 | 1c11bace | Christos Stavrakakis | for the SQL query.
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62 | 1c11bace | Christos Stavrakakis |
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63 | 1c11bace | Christos Stavrakakis | """
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64 | 864bed43 | Christos Stavrakakis | |
65 | 864bed43 | Christos Stavrakakis | def filter(self, *args, **kwargs): |
66 | 1c11bace | Christos Stavrakakis | query = super(ForUpdateQuerySet, self).filter(*args, **kwargs) |
67 | 1c11bace | Christos Stavrakakis | return for_update(query)
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68 | 864bed43 | Christos Stavrakakis | |
69 | 864bed43 | Christos Stavrakakis | def get(self, *args, **kwargs): |
70 | 864bed43 | Christos Stavrakakis | query = self.filter(*args, **kwargs)
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71 | 864bed43 | Christos Stavrakakis | query = list(query)
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72 | 864bed43 | Christos Stavrakakis | num = len(query)
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73 | 864bed43 | Christos Stavrakakis | if num == 1: |
74 | 864bed43 | Christos Stavrakakis | return query[0] |
75 | 864bed43 | Christos Stavrakakis | if not num: |
76 | 68b952f9 | Christos Stavrakakis | raise self.model.DoesNotExist("%s matching query does not exist. " |
77 | 68b952f9 | Christos Stavrakakis | "Lookup parameters were %s" %
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78 | 68b952f9 | Christos Stavrakakis | (self.model._meta.object_name,
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79 | 68b952f9 | Christos Stavrakakis | kwargs)) |
80 | 864bed43 | Christos Stavrakakis | raise self.model.MultipleObjectsReturned( |
81 | 864bed43 | Christos Stavrakakis | "get() returned more than one %s -- it returned %s! "
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82 | 864bed43 | Christos Stavrakakis | "Lookup parameters were %s" %
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83 | 864bed43 | Christos Stavrakakis | (self.model._meta.object_name, num, kwargs))
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84 | 864bed43 | Christos Stavrakakis | |
85 | 864bed43 | Christos Stavrakakis | |
86 | 864bed43 | Christos Stavrakakis | def for_update(query): |
87 | dbecf586 | Christos Stavrakakis | """Rewrite query using SELECT .. FOR UPDATE."""
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88 | 864bed43 | Christos Stavrakakis | if 'sqlite' in connections[query.db].settings_dict['ENGINE'].lower(): |
89 | 864bed43 | Christos Stavrakakis | # SQLite does not support FOR UPDATE
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90 | 864bed43 | Christos Stavrakakis | return query
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91 | 864bed43 | Christos Stavrakakis | sql, params = query.query.get_compiler(query.db).as_sql() |
92 | 864bed43 | Christos Stavrakakis | return query.model._default_manager.raw(sql.rstrip() + ' FOR UPDATE', |
93 | 864bed43 | Christos Stavrakakis | params) |
94 | 864bed43 | Christos Stavrakakis | |
95 | 864bed43 | Christos Stavrakakis | |
96 | adc46059 | Christos Stavrakakis | class ProtectedDeleteManager(ForUpdateManager): |
97 | dbecf586 | Christos Stavrakakis | """Manager for protecting Backend deletion.
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98 | 864bed43 | Christos Stavrakakis |
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99 | dbecf586 | Christos Stavrakakis | Call Backend delete() method in order to prevent deletion
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100 | dbecf586 | Christos Stavrakakis | of Backends that host non-deleted VirtualMachines.
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101 | 864bed43 | Christos Stavrakakis |
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102 | 864bed43 | Christos Stavrakakis | """
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103 | 864bed43 | Christos Stavrakakis | |
104 | 864bed43 | Christos Stavrakakis | def get_query_set(self): |
105 | 864bed43 | Christos Stavrakakis | return BackendQuerySet(self.model, using=self._db) |
106 | 864bed43 | Christos Stavrakakis | |
107 | 864bed43 | Christos Stavrakakis | |
108 | 864bed43 | Christos Stavrakakis | class BackendQuerySet(QuerySet): |
109 | 864bed43 | Christos Stavrakakis | def delete(self): |
110 | 864bed43 | Christos Stavrakakis | for backend in self._clone(): |
111 | 864bed43 | Christos Stavrakakis | backend.delete() |