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annotate pylons_app/model/caching_query.py @ 489:460ad816820d celery

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fixed bug when new repo had no last commiter, fixed bug when my_account updating information failed, by not uniq email address.
author Marcin Kuzminski <marcin@python-works.com>
date Mon, 20 Sep 2010 22:47:20 +0200
parents 7afbc45aab28
children
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1 """caching_query.py
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2
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3 Represent persistence structures which allow the usage of
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4 Beaker caching with SQLAlchemy.
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5
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6 The three new concepts introduced here are:
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7
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8 * CachingQuery - a Query subclass that caches and
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9 retrieves results in/from Beaker.
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10 * FromCache - a query option that establishes caching
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11 parameters on a Query
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12 * RelationshipCache - a variant of FromCache which is specific
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13 to a query invoked during a lazy load.
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14 * _params_from_query - extracts value parameters from
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15 a Query.
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16
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17 The rest of what's here are standard SQLAlchemy and
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18 Beaker constructs.
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19
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20 """
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21 from sqlalchemy.orm.interfaces import MapperOption
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22 from sqlalchemy.orm.query import Query
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23 from sqlalchemy.sql import visitors
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24
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25 class CachingQuery(Query):
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26 """A Query subclass which optionally loads full results from a Beaker
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27 cache region.
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28
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29 The CachingQuery stores additional state that allows it to consult
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30 a Beaker cache before accessing the database:
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31
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32 * A "region", which is a cache region argument passed to a
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33 Beaker CacheManager, specifies a particular cache configuration
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34 (including backend implementation, expiration times, etc.)
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35 * A "namespace", which is a qualifying name that identifies a
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36 group of keys within the cache. A query that filters on a name
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37 might use the name "by_name", a query that filters on a date range
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38 to a joined table might use the name "related_date_range".
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39
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40 When the above state is present, a Beaker cache is retrieved.
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41
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42 The "namespace" name is first concatenated with
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43 a string composed of the individual entities and columns the Query
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44 requests, i.e. such as ``Query(User.id, User.name)``.
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45
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46 The Beaker cache is then loaded from the cache manager based
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47 on the region and composed namespace. The key within the cache
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48 itself is then constructed against the bind parameters specified
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49 by this query, which are usually literals defined in the
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50 WHERE clause.
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51
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52 The FromCache and RelationshipCache mapper options below represent
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53 the "public" method of configuring this state upon the CachingQuery.
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54
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55 """
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56
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57 def __init__(self, manager, *args, **kw):
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58 self.cache_manager = manager
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59 Query.__init__(self, *args, **kw)
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60
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61 def __iter__(self):
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62 """override __iter__ to pull results from Beaker
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63 if particular attributes have been configured.
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64
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65 Note that this approach does *not* detach the loaded objects from
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66 the current session. If the cache backend is an in-process cache
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67 (like "memory") and lives beyond the scope of the current session's
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68 transaction, those objects may be expired. The method here can be
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69 modified to first expunge() each loaded item from the current
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70 session before returning the list of items, so that the items
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71 in the cache are not the same ones in the current Session.
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72
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73 """
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74 if hasattr(self, '_cache_parameters'):
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75 return self.get_value(createfunc=lambda: list(Query.__iter__(self)))
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76 else:
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77 return Query.__iter__(self)
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78
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79 def invalidate(self):
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80 """Invalidate the value represented by this Query."""
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81
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82 cache, cache_key = _get_cache_parameters(self)
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83 cache.remove(cache_key)
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84
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85 def get_value(self, merge=True, createfunc=None):
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86 """Return the value from the cache for this query.
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87
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88 Raise KeyError if no value present and no
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89 createfunc specified.
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90
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91 """
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92 cache, cache_key = _get_cache_parameters(self)
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93 ret = cache.get_value(cache_key, createfunc=createfunc)
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94 if merge:
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95 ret = self.merge_result(ret, load=False)
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96 return ret
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97
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98 def set_value(self, value):
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99 """Set the value in the cache for this query."""
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100
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101 cache, cache_key = _get_cache_parameters(self)
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102 cache.put(cache_key, value)
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103
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104 def query_callable(manager):
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105 def query(*arg, **kw):
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106 return CachingQuery(manager, *arg, **kw)
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107 return query
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108
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109 def _get_cache_parameters(query):
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110 """For a query with cache_region and cache_namespace configured,
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111 return the correspoinding Cache instance and cache key, based
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112 on this query's current criterion and parameter values.
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113
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114 """
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115 if not hasattr(query, '_cache_parameters'):
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116 raise ValueError("This Query does not have caching parameters configured.")
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117
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118 region, namespace, cache_key = query._cache_parameters
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119
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120 namespace = _namespace_from_query(namespace, query)
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121
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122 if cache_key is None:
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123 # cache key - the value arguments from this query's parameters.
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124 args = _params_from_query(query)
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125 cache_key = " ".join([str(x) for x in args])
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126
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127 # get cache
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128 cache = query.cache_manager.get_cache_region(namespace, region)
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129
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130 # optional - hash the cache_key too for consistent length
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131 # import uuid
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132 # cache_key= str(uuid.uuid5(uuid.NAMESPACE_DNS, cache_key))
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133
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134 return cache, cache_key
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135
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136 def _namespace_from_query(namespace, query):
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137 # cache namespace - the token handed in by the
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138 # option + class we're querying against
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139 namespace = " ".join([namespace] + [str(x) for x in query._entities])
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140
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141 # memcached wants this
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142 namespace = namespace.replace(' ', '_')
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143
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144 return namespace
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145
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146 def _set_cache_parameters(query, region, namespace, cache_key):
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147
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148 if hasattr(query, '_cache_parameters'):
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149 region, namespace, cache_key = query._cache_parameters
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150 raise ValueError("This query is already configured "
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151 "for region %r namespace %r" %
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152 (region, namespace)
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153 )
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154 query._cache_parameters = region, namespace, cache_key
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155
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156 class FromCache(MapperOption):
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157 """Specifies that a Query should load results from a cache."""
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158
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159 propagate_to_loaders = False
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160
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161 def __init__(self, region, namespace, cache_key=None):
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162 """Construct a new FromCache.
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163
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164 :param region: the cache region. Should be a
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165 region configured in the Beaker CacheManager.
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166
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167 :param namespace: the cache namespace. Should
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168 be a name uniquely describing the target Query's
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169 lexical structure.
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170
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171 :param cache_key: optional. A string cache key
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172 that will serve as the key to the query. Use this
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173 if your query has a huge amount of parameters (such
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174 as when using in_()) which correspond more simply to
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175 some other identifier.
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176
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177 """
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178 self.region = region
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179 self.namespace = namespace
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180 self.cache_key = cache_key
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181
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182 def process_query(self, query):
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183 """Process a Query during normal loading operation."""
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184
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185 _set_cache_parameters(query, self.region, self.namespace, self.cache_key)
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186
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187 class RelationshipCache(MapperOption):
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188 """Specifies that a Query as called within a "lazy load"
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189 should load results from a cache."""
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190
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191 propagate_to_loaders = True
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192
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193 def __init__(self, region, namespace, attribute):
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194 """Construct a new RelationshipCache.
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195
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196 :param region: the cache region. Should be a
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197 region configured in the Beaker CacheManager.
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198
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199 :param namespace: the cache namespace. Should
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200 be a name uniquely describing the target Query's
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201 lexical structure.
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202
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203 :param attribute: A Class.attribute which
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204 indicates a particular class relationship() whose
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205 lazy loader should be pulled from the cache.
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206
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207 """
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208 self.region = region
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209 self.namespace = namespace
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210 self._relationship_options = {
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211 (attribute.property.parent.class_, attribute.property.key) : self
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212 }
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213
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214 def process_query_conditionally(self, query):
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215 """Process a Query that is used within a lazy loader.
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216
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217 (the process_query_conditionally() method is a SQLAlchemy
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218 hook invoked only within lazyload.)
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219
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220 """
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221 if query._current_path:
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222 mapper, key = query._current_path[-2:]
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223
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224 for cls in mapper.class_.__mro__:
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225 if (cls, key) in self._relationship_options:
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226 relationship_option = self._relationship_options[(cls, key)]
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227 _set_cache_parameters(
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228 query,
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229 relationship_option.region,
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230 relationship_option.namespace,
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231 None)
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232
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233 def and_(self, option):
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234 """Chain another RelationshipCache option to this one.
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235
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236 While many RelationshipCache objects can be specified on a single
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237 Query separately, chaining them together allows for a more efficient
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238 lookup during load.
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239
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240 """
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241 self._relationship_options.update(option._relationship_options)
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242 return self
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243
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244
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245 def _params_from_query(query):
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246 """Pull the bind parameter values from a query.
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247
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248 This takes into account any scalar attribute bindparam set up.
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249
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250 E.g. params_from_query(query.filter(Cls.foo==5).filter(Cls.bar==7)))
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251 would return [5, 7].
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252
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253 """
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254 v = []
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255 def visit_bindparam(bind):
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256 value = query._params.get(bind.key, bind.value)
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257
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258 # lazyloader may dig a callable in here, intended
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259 # to late-evaluate params after autoflush is called.
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260 # convert to a scalar value.
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261 if callable(value):
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262 value = value()
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263
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264 v.append(value)
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265 if query._criterion is not None:
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266 visitors.traverse(query._criterion, {}, {'bindparam':visit_bindparam})
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267 return v