author | Pawel Solyga <Pawel.Solyga@gmail.com> |
Mon, 01 Jun 2009 20:31:38 +0200 | |
changeset 2373 | 05ab9393303d |
parent 2309 | be1b94099f2d |
child 2413 | d0b7dac5325c |
permissions | -rwxr-xr-x |
#!/usr/bin/env python # # Copyright 2007 Google Inc. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. # """The Python datastore API used by app developers. Defines Entity, Query, and Iterator classes, as well as methods for all of the datastore's calls. Also defines conversions between the Python classes and their PB counterparts. The datastore errors are defined in the datastore_errors module. That module is only required to avoid circular imports. datastore imports datastore_types, which needs BadValueError, so it can't be defined in datastore. """ import heapq import itertools import logging import re import string import sys import traceback from xml.sax import saxutils from google.appengine.api import api_base_pb from google.appengine.api import apiproxy_stub_map from google.appengine.api import datastore_errors from google.appengine.api import datastore_types from google.appengine.datastore import datastore_index from google.appengine.datastore import datastore_pb from google.appengine.runtime import apiproxy_errors from google.appengine.datastore import entity_pb MAX_ALLOWABLE_QUERIES = 30 DEFAULT_TRANSACTION_RETRIES = 3 _MAX_INDEXED_PROPERTIES = 5000 Key = datastore_types.Key typename = datastore_types.typename _txes = {} def NormalizeAndTypeCheck(arg, types): """Normalizes and type checks the given argument. Args: arg: an instance, tuple, list, iterator, or generator of the given type(s) types: allowed type or tuple of types Returns: A (list, bool) tuple. The list is a normalized, shallow copy of the argument. The boolean is True if the argument was a sequence, False if it was a single object. Raises: AssertionError: types includes list or tuple. BadArgumentError: arg is not an instance or sequence of one of the given types. """ if not isinstance(types, (list, tuple)): types = (types,) assert list not in types and tuple not in types if isinstance(arg, types): return ([arg], False) else: try: for val in arg: if not isinstance(val, types): raise datastore_errors.BadArgumentError( 'Expected one of %s; received %s (a %s).' % (types, val, typename(val))) except TypeError: raise datastore_errors.BadArgumentError( 'Expected an instance or sequence of %s; received %s (a %s).' % (types, arg, typename(arg))) return (list(arg), True) def NormalizeAndTypeCheckKeys(keys): """Normalizes and type checks that the given argument is a valid key or keys. A wrapper around NormalizeAndTypeCheck() that accepts strings, Keys, and Entities, and normalizes to Keys. Args: keys: a Key or sequence of Keys Returns: A (list of Keys, bool) tuple. See NormalizeAndTypeCheck. Raises: BadArgumentError: arg is not an instance or sequence of one of the given types. """ keys, multiple = NormalizeAndTypeCheck(keys, (basestring, Entity, Key)) keys = [_GetCompleteKeyOrError(key) for key in keys] return (keys, multiple) def Put(entities): """Store one or more entities in the datastore. The entities may be new or previously existing. For new entities, Put() will fill in the app id and key assigned by the datastore. If the argument is a single Entity, a single Key will be returned. If the argument is a list of Entity, a list of Keys will be returned. Args: entities: Entity or list of Entities Returns: Key or list of Keys Raises: TransactionFailedError, if the Put could not be committed. """ entities, multiple = NormalizeAndTypeCheck(entities, Entity) if multiple and not entities: return [] for entity in entities: if not entity.kind() or not entity.app(): raise datastore_errors.BadRequestError( 'App and kind must not be empty, in entity: %s' % entity) req = datastore_pb.PutRequest() req.entity_list().extend([e._ToPb() for e in entities]) keys = [e.key() for e in entities] tx = _MaybeSetupTransaction(req, keys) if tx: tx.RecordModifiedKeys([k for k in keys if k.has_id_or_name()]) resp = datastore_pb.PutResponse() try: apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Put', req, resp) except apiproxy_errors.ApplicationError, err: raise _ToDatastoreError(err) keys = resp.key_list() num_keys = len(keys) num_entities = len(entities) if num_keys != num_entities: raise datastore_errors.InternalError( 'Put accepted %d entities but returned %d keys.' % (num_entities, num_keys)) for entity, key in zip(entities, keys): entity._Entity__key._Key__reference.CopyFrom(key) if tx: tx.RecordModifiedKeys([e.key() for e in entities], error_on_repeat=False) if multiple: return [Key._FromPb(k) for k in keys] else: return Key._FromPb(resp.key(0)) def Get(keys): """Retrieves one or more entities from the datastore. Retrieves the entity or entities with the given key(s) from the datastore and returns them as fully populated Entity objects, as defined below. If there is an error, raises a subclass of datastore_errors.Error. If keys is a single key or string, an Entity will be returned, or EntityNotFoundError will be raised if no existing entity matches the key. However, if keys is a list or tuple, a list of entities will be returned that corresponds to the sequence of keys. It will include entities for keys that were found and None placeholders for keys that were not found. Args: # the primary key(s) of the entity(ies) to retrieve keys: Key or string or list of Keys or strings Returns: Entity or list of Entity objects """ keys, multiple = NormalizeAndTypeCheckKeys(keys) if multiple and not keys: return [] req = datastore_pb.GetRequest() req.key_list().extend([key._Key__reference for key in keys]) _MaybeSetupTransaction(req, keys) resp = datastore_pb.GetResponse() try: apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Get', req, resp) except apiproxy_errors.ApplicationError, err: raise _ToDatastoreError(err) entities = [] for group in resp.entity_list(): if group.has_entity(): entities.append(Entity._FromPb(group.entity())) else: entities.append(None) if multiple: return entities else: if entities[0] is None: raise datastore_errors.EntityNotFoundError() return entities[0] def Delete(keys): """Deletes one or more entities from the datastore. Use with care! Deletes the given entity(ies) from the datastore. You can only delete entities from your app. If there is an error, raises a subclass of datastore_errors.Error. Args: # the primary key(s) of the entity(ies) to delete keys: Key or string or list of Keys or strings Raises: TransactionFailedError, if the Delete could not be committed. """ keys, multiple = NormalizeAndTypeCheckKeys(keys) if multiple and not keys: return req = datastore_pb.DeleteRequest() req.key_list().extend([key._Key__reference for key in keys]) tx = _MaybeSetupTransaction(req, keys) if tx: tx.RecordModifiedKeys(keys) resp = datastore_pb.DeleteResponse() try: apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Delete', req, resp) except apiproxy_errors.ApplicationError, err: raise _ToDatastoreError(err) class Entity(dict): """A datastore entity. Includes read-only accessors for app id, kind, and primary key. Also provides dictionary-style access to properties. """ def __init__(self, kind, parent=None, _app=None, name=None, unindexed_properties=[]): """Constructor. Takes the kind and transaction root, which cannot be changed after the entity is constructed, and an optional parent. Raises BadArgumentError or BadKeyError if kind is invalid or parent is not an existing Entity or Key in the datastore. Args: # this entity's kind kind: string # if provided, this entity's parent. Its key must be complete. parent: Entity or Key # if provided, this entity's name. name: string # if provided, a sequence of property names that should not be indexed # by the built-in single property indices. unindexed_properties: list or tuple of strings """ ref = entity_pb.Reference() _app = datastore_types.ResolveAppId(_app) ref.set_app(_app) datastore_types.ValidateString(kind, 'kind', datastore_errors.BadArgumentError) if parent is not None: parent = _GetCompleteKeyOrError(parent) if _app != parent.app(): raise datastore_errors.BadArgumentError( "_app %s doesn't match parent's app %s" % (_app, parent.app())) ref.CopyFrom(parent._Key__reference) last_path = ref.mutable_path().add_element() last_path.set_type(kind.encode('utf-8')) if name is not None: datastore_types.ValidateString(name, 'name') if name[0] in string.digits: raise datastore_errors.BadValueError('name cannot begin with a digit') last_path.set_name(name.encode('utf-8')) unindexed_properties, multiple = NormalizeAndTypeCheck(unindexed_properties, basestring) if not multiple: raise datastore_errors.BadArgumentError( 'unindexed_properties must be a sequence; received %s (a %s).' % (unindexed_properties, typename(unindexed_properties))) for prop in unindexed_properties: datastore_types.ValidateProperty(prop, None) self.__unindexed_properties = frozenset(unindexed_properties) self.__key = Key._FromPb(ref) def app(self): """Returns the name of the application that created this entity, a string. """ return self.__key.app() def kind(self): """Returns this entity's kind, a string. """ return self.__key.kind() def key(self): """Returns this entity's primary key, a Key instance. """ return self.__key def parent(self): """Returns this entity's parent, as a Key. If this entity has no parent, returns None. """ return self.key().parent() def entity_group(self): """Returns this entity's entity group as a Key. Note that the returned Key will be incomplete if this is a a root entity and its key is incomplete. """ return self.key().entity_group() def unindexed_properties(self): """Returns this entity's unindexed properties, as a frozenset of strings.""" return self.__unindexed_properties def __setitem__(self, name, value): """Implements the [] operator. Used to set property value(s). If the property name is the empty string or not a string, raises BadPropertyError. If the value is not a supported type, raises BadValueError. """ datastore_types.ValidateProperty(name, value) dict.__setitem__(self, name, value) def setdefault(self, name, value): """If the property exists, returns its value. Otherwise sets it to value. If the property name is the empty string or not a string, raises BadPropertyError. If the value is not a supported type, raises BadValueError. """ datastore_types.ValidateProperty(name, value) return dict.setdefault(self, name, value) def update(self, other): """Updates this entity's properties from the values in other. If any property name is the empty string or not a string, raises BadPropertyError. If any value is not a supported type, raises BadValueError. """ for name, value in other.items(): self.__setitem__(name, value) def copy(self): """The copy method is not supported. """ raise NotImplementedError('Entity does not support the copy() method.') def ToXml(self): """Returns an XML representation of this entity. Atom and gd:namespace properties are converted to XML according to their respective schemas. For more information, see: http://www.atomenabled.org/developers/syndication/ http://code.google.com/apis/gdata/common-elements.html This is *not* optimized. It shouldn't be used anywhere near code that's performance-critical. """ xml = u'<entity kind=%s' % saxutils.quoteattr(self.kind()) if self.__key.has_id_or_name(): xml += ' key=%s' % saxutils.quoteattr(str(self.__key)) xml += '>' if self.__key.has_id_or_name(): xml += '\n <key>%s</key>' % self.__key.ToTagUri() properties = self.keys() if properties: properties.sort() xml += '\n ' + '\n '.join(self._PropertiesToXml(properties)) xml += '\n</entity>\n' return xml def _PropertiesToXml(self, properties): """ Returns a list of the XML representations of each of the given properties. Ignores properties that don't exist in this entity. Arg: properties: string or list of strings Returns: list of strings """ xml_properties = [] for propname in properties: if not self.has_key(propname): continue propname_xml = saxutils.quoteattr(propname) values = self[propname] if not isinstance(values, list): values = [values] proptype = datastore_types.PropertyTypeName(values[0]) proptype_xml = saxutils.quoteattr(proptype) escaped_values = self._XmlEscapeValues(propname) open_tag = u'<property name=%s type=%s>' % (propname_xml, proptype_xml) close_tag = u'</property>' xml_properties += [open_tag + val + close_tag for val in escaped_values] return xml_properties def _XmlEscapeValues(self, property): """ Returns a list of the XML-escaped string values for the given property. Raises an AssertionError if the property doesn't exist. Arg: property: string Returns: list of strings """ assert self.has_key(property) xml = [] values = self[property] if not isinstance(values, list): values = [values] for val in values: if hasattr(val, 'ToXml'): xml.append(val.ToXml()) else: if val is None: xml.append('') else: xml.append(saxutils.escape(unicode(val))) return xml def _ToPb(self): """Converts this Entity to its protocol buffer representation. Not intended to be used by application developers. Returns: entity_pb.Entity """ pb = entity_pb.EntityProto() pb.mutable_key().CopyFrom(self.key()._ToPb()) group = pb.mutable_entity_group() if self.__key.has_id_or_name(): root = pb.key().path().element(0) group.add_element().CopyFrom(root) properties = self.items() properties.sort() for (name, values) in properties: properties = datastore_types.ToPropertyPb(name, values) if not isinstance(properties, list): properties = [properties] sample = values if isinstance(sample, list): sample = values[0] if (isinstance(sample, datastore_types._RAW_PROPERTY_TYPES) or name in self.__unindexed_properties): pb.raw_property_list().extend(properties) else: pb.property_list().extend(properties) if pb.property_size() > _MAX_INDEXED_PROPERTIES: raise datastore_errors.BadRequestError( 'Too many indexed properties for entity %r.' % self.key()) return pb @staticmethod def _FromPb(pb): """Static factory method. Returns the Entity representation of the given protocol buffer (datastore_pb.Entity). Not intended to be used by application developers. The Entity PB's key must be complete. If it isn't, an AssertionError is raised. Args: # a protocol buffer Entity pb: datastore_pb.Entity Returns: # the Entity representation of the argument Entity """ assert pb.key().path().element_size() > 0 last_path = pb.key().path().element_list()[-1] assert last_path.has_id() ^ last_path.has_name() if last_path.has_id(): assert last_path.id() != 0 else: assert last_path.has_name() assert last_path.name() unindexed_properties = [p.name() for p in pb.raw_property_list()] e = Entity(unicode(last_path.type().decode('utf-8')), unindexed_properties=unindexed_properties) ref = e.__key._Key__reference ref.CopyFrom(pb.key()) temporary_values = {} for prop_list in (pb.property_list(), pb.raw_property_list()): for prop in prop_list: try: value = datastore_types.FromPropertyPb(prop) except (AssertionError, AttributeError, TypeError, ValueError), e: raise datastore_errors.Error( 'Property %s is corrupt in the datastore. %s: %s' % (e.__class__, prop.name(), e)) multiple = prop.multiple() if multiple: value = [value] name = prop.name() cur_value = temporary_values.get(name) if cur_value is None: temporary_values[name] = value elif not multiple: raise datastore_errors.Error( 'Property %s is corrupt in the datastore; it has multiple ' 'values, but is not marked as multiply valued.' % name) else: cur_value.extend(value) for name, value in temporary_values.iteritems(): decoded_name = unicode(name.decode('utf-8')) datastore_types.ValidateReadProperty(decoded_name, value) dict.__setitem__(e, decoded_name, value) return e class Query(dict): """A datastore query. (Instead of this, consider using appengine.ext.gql.Query! It provides a query language interface on top of the same functionality.) Queries are used to retrieve entities that match certain criteria, including app id, kind, and property filters. Results may also be sorted by properties. App id and kind are required. Only entities from the given app, of the given type, are returned. If an ancestor is set, with Ancestor(), only entities with that ancestor are returned. Property filters are used to provide criteria based on individual property values. A filter compares a specific property in each entity to a given value or list of possible values. An entity is returned if its property values match *all* of the query's filters. In other words, filters are combined with AND, not OR. If an entity does not have a value for a property used in a filter, it is not returned. Property filters map filter strings of the form '<property name> <operator>' to filter values. Use dictionary accessors to set property filters, like so: > query = Query('Person') > query['name ='] = 'Ryan' > query['age >='] = 21 This query returns all Person entities where the name property is 'Ryan', 'Ken', or 'Bret', and the age property is at least 21. Another way to build this query is: > query = Query('Person') > query.update({'name =': 'Ryan', 'age >=': 21}) The supported operators are =, >, <, >=, and <=. Only one inequality filter may be used per query. Any number of equals filters may be used in a single Query. A filter value may be a list or tuple of values. This is interpreted as multiple filters with the same filter string and different values, all ANDed together. For example, this query returns everyone with the tags "google" and "app engine": > Query('Person', {'tag =': ('google', 'app engine')}) Result entities can be returned in different orders. Use the Order() method to specify properties that results will be sorted by, and in which direction. Note that filters and orderings may be provided at any time before the query is run. When the query is fully specified, Run() runs the query and returns an iterator. The query results can be accessed through the iterator. A query object may be reused after it's been run. Its filters and orderings can be changed to create a modified query. If you know how many result entities you need, use Get() to fetch them: > query = Query('Person', {'age >': 21}) > for person in query.Get(4): > print 'I have four pints left. Have one on me, %s!' % person['name'] If you don't know how many results you need, or if you need them all, you can get an iterator over the results by calling Run(): > for person in Query('Person', {'age >': 21}).Run(): > print 'Have a pint on me, %s!' % person['name'] Get() is more efficient than Run(), so use Get() whenever possible. Finally, the Count() method returns the number of result entities matched by the query. The returned count is cached; successive Count() calls will not re-scan the datastore unless the query is changed. """ ASCENDING = datastore_pb.Query_Order.ASCENDING DESCENDING = datastore_pb.Query_Order.DESCENDING ORDER_FIRST = datastore_pb.Query.ORDER_FIRST ANCESTOR_FIRST = datastore_pb.Query.ANCESTOR_FIRST FILTER_FIRST = datastore_pb.Query.FILTER_FIRST OPERATORS = {'<': datastore_pb.Query_Filter.LESS_THAN, '<=': datastore_pb.Query_Filter.LESS_THAN_OR_EQUAL, '>': datastore_pb.Query_Filter.GREATER_THAN, '>=': datastore_pb.Query_Filter.GREATER_THAN_OR_EQUAL, '=': datastore_pb.Query_Filter.EQUAL, '==': datastore_pb.Query_Filter.EQUAL, } INEQUALITY_OPERATORS = frozenset(['<', '<=', '>', '>=']) FILTER_REGEX = re.compile( '^\s*([^\s]+)(\s+(%s)\s*)?$' % '|'.join(OPERATORS.keys()), re.IGNORECASE | re.UNICODE) __kind = None __app = None __orderings = None __cached_count = None __hint = None __ancestor = None __filter_order = None __filter_counter = 0 __inequality_prop = None __inequality_count = 0 def __init__(self, kind, filters={}, _app=None, keys_only=False): """Constructor. Raises BadArgumentError if kind is not a string. Raises BadValueError or BadFilterError if filters is not a dictionary of valid filters. Args: # kind is required. filters is optional; if provided, it's used # as an initial set of property filters. keys_only defaults to False. kind: string filters: dict keys_only: boolean """ datastore_types.ValidateString(kind, 'kind', datastore_errors.BadArgumentError) self.__kind = kind self.__orderings = [] self.__filter_order = {} self.update(filters) self.__app = datastore_types.ResolveAppId(_app) self.__keys_only = keys_only def Order(self, *orderings): """Specify how the query results should be sorted. Result entities will be sorted by the first property argument, then by the second, and so on. For example, this: > query = Query('Person') > query.Order('bday', ('age', Query.DESCENDING)) sorts everyone in order of their birthday, starting with January 1. People with the same birthday are sorted by age, oldest to youngest. The direction for each sort property may be provided; if omitted, it defaults to ascending. Order() may be called multiple times. Each call resets the sort order from scratch. If an inequality filter exists in this Query it must be the first property passed to Order. Any number of sort orders may be used after the inequality filter property. Without inequality filters, any number of filters with different orders may be specified. Entities with multiple values for an order property are sorted by their lowest value. Note that a sort order implies an existence filter! In other words, Entities without the sort order property are filtered out, and *not* included in the query results. If the sort order property has different types in different entities - ie, if bob['id'] is an int and fred['id'] is a string - the entities will be grouped first by the property type, then sorted within type. No attempt is made to compare property values across types. Raises BadArgumentError if any argument is of the wrong format. Args: # the properties to sort by, in sort order. each argument may be either a # string or (string, direction) 2-tuple. Returns: # this query Query """ orderings = list(orderings) for (order, i) in zip(orderings, range(len(orderings))): if not (isinstance(order, basestring) or (isinstance(order, tuple) and len(order) in [2, 3])): raise datastore_errors.BadArgumentError( 'Order() expects strings or 2- or 3-tuples; received %s (a %s). ' % (order, typename(order))) if isinstance(order, basestring): order = (order,) datastore_types.ValidateString(order[0], 'sort order property', datastore_errors.BadArgumentError) property = order[0] direction = order[-1] if direction not in (Query.ASCENDING, Query.DESCENDING): if len(order) == 3: raise datastore_errors.BadArgumentError( 'Order() expects Query.ASCENDING or DESCENDING; received %s' % str(direction)) direction = Query.ASCENDING orderings[i] = (property, direction) if (orderings and self.__inequality_prop and orderings[0][0] != self.__inequality_prop): raise datastore_errors.BadArgumentError( 'First ordering property must be the same as inequality filter ' 'property, if specified for this query; received %s, expected %s' % (orderings[0][0], self.__inequality_prop)) self.__orderings = orderings return self def Hint(self, hint): """Sets a hint for how this query should run. The query hint gives us information about how best to execute your query. Currently, we can only do one index scan, so the query hint should be used to indicates which index we should scan against. Use FILTER_FIRST if your first filter will only match a few results. In this case, it will be most efficient to scan against the index for this property, load the results into memory, and apply the remaining filters and sort orders there. Similarly, use ANCESTOR_FIRST if the query's ancestor only has a few descendants. In this case, it will be most efficient to scan all entities below the ancestor and load them into memory first. Use ORDER_FIRST if the query has a sort order and the result set is large or you only plan to fetch the first few results. In that case, we shouldn't try to load all of the results into memory; instead, we should scan the index for this property, which is in sorted order. Note that hints are currently ignored in the v3 datastore! Arg: one of datastore.Query.[ORDER_FIRST, ANCESTOR_FIRST, FILTER_FIRST] Returns: # this query Query """ if hint not in [self.ORDER_FIRST, self.ANCESTOR_FIRST, self.FILTER_FIRST]: raise datastore_errors.BadArgumentError( 'Query hint must be ORDER_FIRST, ANCESTOR_FIRST, or FILTER_FIRST.') self.__hint = hint return self def Ancestor(self, ancestor): """Sets an ancestor for this query. This restricts the query to only return result entities that are descended from a given entity. In other words, all of the results will have the ancestor as their parent, or parent's parent, or etc. Raises BadArgumentError or BadKeyError if parent is not an existing Entity or Key in the datastore. Args: # the key must be complete ancestor: Entity or Key Returns: # this query Query """ key = _GetCompleteKeyOrError(ancestor) self.__ancestor = datastore_pb.Reference() self.__ancestor.CopyFrom(key._Key__reference) return self def IsKeysOnly(self): """Returns True if this query is keys only, false otherwise.""" return self.__keys_only def Run(self): """Runs this query. If a filter string is invalid, raises BadFilterError. If a filter value is invalid, raises BadValueError. If an IN filter is provided, and a sort order on another property is provided, raises BadQueryError. If you know in advance how many results you want, use Get() instead. It's more efficient. Returns: # an iterator that provides access to the query results Iterator """ return self._Run() def _Run(self, limit=None, offset=None): """Runs this query, with an optional result limit and an optional offset. Identical to Run, with the extra optional limit and offset parameters. limit and offset must both be integers >= 0. This is not intended to be used by application developers. Use Get() instead! """ if _CurrentTransactionKey(): raise datastore_errors.BadRequestError( "Can't query inside a transaction.") pb = self._ToPb(limit, offset) result = datastore_pb.QueryResult() try: apiproxy_stub_map.MakeSyncCall('datastore_v3', 'RunQuery', pb, result) except apiproxy_errors.ApplicationError, err: try: _ToDatastoreError(err) except datastore_errors.NeedIndexError, exc: yaml = datastore_index.IndexYamlForQuery( *datastore_index.CompositeIndexForQuery(pb)[1:-1]) raise datastore_errors.NeedIndexError( str(exc) + '\nThis query needs this index:\n' + yaml) return Iterator._FromPb(result) def Get(self, limit, offset=0): """Fetches and returns a maximum number of results from the query. This method fetches and returns a list of resulting entities that matched the query. If the query specified a sort order, entities are returned in that order. Otherwise, the order is undefined. The limit argument specifies the maximum number of entities to return. If it's greater than the number of remaining entities, all of the remaining entities are returned. In that case, the length of the returned list will be smaller than limit. The offset argument specifies the number of entities that matched the query criteria to skip before starting to return results. The limit is applied after the offset, so if you provide a limit of 10 and an offset of 5 and your query matches 20 records, the records whose index is 0 through 4 will be skipped and the records whose index is 5 through 14 will be returned. The results are always returned as a list. If there are no results left, an empty list is returned. If you know in advance how many results you want, this method is more efficient than Run(), since it fetches all of the results at once. (The datastore backend sets the the limit on the underlying scan, which makes the scan significantly faster.) Args: # the maximum number of entities to return int or long # the number of entities to skip int or long Returns: # a list of entities [Entity, ...] """ if not isinstance(limit, (int, long)) or limit <= 0: raise datastore_errors.BadArgumentError( 'Argument to Get named \'limit\' must be an int greater than 0; ' 'received %s (a %s)' % (limit, typename(limit))) if not isinstance(offset, (int, long)) or offset < 0: raise datastore_errors.BadArgumentError( 'Argument to Get named \'offset\' must be an int greater than or ' 'equal to 0; received %s (a %s)' % (offset, typename(offset))) return self._Run(limit, offset)._Next(limit) def Count(self, limit=None): """Returns the number of entities that this query matches. The returned count is cached; successive Count() calls will not re-scan the datastore unless the query is changed. Args: limit, a number. If there are more results than this, stop short and just return this number. Providing this argument makes the count operation more efficient. Returns: The number of results. """ if self.__cached_count: return self.__cached_count resp = api_base_pb.Integer64Proto() try: apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Count', self._ToPb(limit=limit), resp) except apiproxy_errors.ApplicationError, err: raise _ToDatastoreError(err) else: self.__cached_count = resp.value() return self.__cached_count def __iter__(self): raise NotImplementedError( 'Query objects should not be used as iterators. Call Run() first.') def __setitem__(self, filter, value): """Implements the [] operator. Used to set filters. If the filter string is empty or not a string, raises BadFilterError. If the value is not a supported type, raises BadValueError. """ if isinstance(value, tuple): value = list(value) datastore_types.ValidateProperty(' ', value, read_only=True) match = self._CheckFilter(filter, value) property = match.group(1) operator = match.group(3) dict.__setitem__(self, filter, value) if operator in self.INEQUALITY_OPERATORS: if self.__inequality_prop is None: self.__inequality_prop = property else: assert self.__inequality_prop == property self.__inequality_count += 1 if filter not in self.__filter_order: self.__filter_order[filter] = self.__filter_counter self.__filter_counter += 1 self.__cached_count = None def setdefault(self, filter, value): """If the filter exists, returns its value. Otherwise sets it to value. If the property name is the empty string or not a string, raises BadPropertyError. If the value is not a supported type, raises BadValueError. """ datastore_types.ValidateProperty(' ', value) self._CheckFilter(filter, value) self.__cached_count = None return dict.setdefault(self, filter, value) def __delitem__(self, filter): """Implements the del [] operator. Used to remove filters. """ dict.__delitem__(self, filter) del self.__filter_order[filter] self.__cached_count = None match = Query.FILTER_REGEX.match(filter) property = match.group(1) operator = match.group(3) if operator in self.INEQUALITY_OPERATORS: assert self.__inequality_count >= 1 assert property == self.__inequality_prop self.__inequality_count -= 1 if self.__inequality_count == 0: self.__inequality_prop = None def update(self, other): """Updates this query's filters from the ones in other. If any filter string is invalid, raises BadFilterError. If any value is not a supported type, raises BadValueError. """ for filter, value in other.items(): self.__setitem__(filter, value) def copy(self): """The copy method is not supported. """ raise NotImplementedError('Query does not support the copy() method.') def _CheckFilter(self, filter, values): """Type check a filter string and list of values. Raises BadFilterError if the filter string is empty, not a string, or invalid. Raises BadValueError if the value type is not supported. Args: filter: String containing the filter text. values: List of associated filter values. Returns: re.MatchObject (never None) that matches the 'filter'. Group 1 is the property name, group 3 is the operator. (Group 2 is unused.) """ try: match = Query.FILTER_REGEX.match(filter) if not match: raise datastore_errors.BadFilterError( 'Could not parse filter string: %s' % str(filter)) except TypeError: raise datastore_errors.BadFilterError( 'Could not parse filter string: %s' % str(filter)) property = match.group(1) operator = match.group(3) if operator is None: operator = '=' if isinstance(values, tuple): values = list(values) elif not isinstance(values, list): values = [values] if isinstance(values[0], datastore_types._RAW_PROPERTY_TYPES): raise datastore_errors.BadValueError( 'Filtering on %s properties is not supported.' % typename(values[0])) if operator in self.INEQUALITY_OPERATORS: if self.__inequality_prop and property != self.__inequality_prop: raise datastore_errors.BadFilterError( 'Only one property per query may have inequality filters (%s).' % ', '.join(self.INEQUALITY_OPERATORS)) elif len(self.__orderings) >= 1 and self.__orderings[0][0] != property: raise datastore_errors.BadFilterError( 'Inequality operators (%s) must be on the same property as the ' 'first sort order, if any sort orders are supplied' % ', '.join(self.INEQUALITY_OPERATORS)) if property in datastore_types._SPECIAL_PROPERTIES: if property == datastore_types._KEY_SPECIAL_PROPERTY: for value in values: if not isinstance(value, Key): raise datastore_errors.BadFilterError( '%s filter value must be a Key; received %s (a %s)' % (datastore_types._KEY_SPECIAL_PROPERTY, value, typename(value))) return match def _ToPb(self, limit=None, offset=None): """Converts this Query to its protocol buffer representation. Not intended to be used by application developers. Enforced by hiding the datastore_pb classes. Args: # an upper bound on the number of results returned by the query. limit: int # number of results that match the query to skip. limit is applied # after the offset is fulfilled offset: int Returns: # the PB representation of this Query datastore_pb.Query """ pb = datastore_pb.Query() pb.set_kind(self.__kind.encode('utf-8')) pb.set_keys_only(bool(self.__keys_only)) if self.__app: pb.set_app(self.__app.encode('utf-8')) if limit is not None: pb.set_limit(limit) if offset is not None: pb.set_offset(offset) if self.__ancestor: pb.mutable_ancestor().CopyFrom(self.__ancestor) if ((self.__hint == self.ORDER_FIRST and self.__orderings) or (self.__hint == self.ANCESTOR_FIRST and self.__ancestor) or (self.__hint == self.FILTER_FIRST and len(self) > 0)): pb.set_hint(self.__hint) ordered_filters = [(i, f) for f, i in self.__filter_order.iteritems()] ordered_filters.sort() for i, filter_str in ordered_filters: if filter_str not in self: continue values = self[filter_str] match = self._CheckFilter(filter_str, values) name = match.group(1) props = datastore_types.ToPropertyPb(name, values) if not isinstance(props, list): props = [props] op = match.group(3) if op is None: op = '=' for prop in props: filter = pb.add_filter() filter.set_op(self.OPERATORS[op]) filter.add_property().CopyFrom(prop) for property, direction in self.__orderings: order = pb.add_order() order.set_property(property.encode('utf-8')) order.set_direction(direction) return pb class MultiQuery(Query): """Class representing a query which requires multiple datastore queries. This class is actually a subclass of datastore.Query as it is intended to act like a normal Query object (supporting the same interface). Does not support keys only queries, since it needs whole entities in order to merge sort them. (That's not true if there are no sort orders, or if the sort order is on __key__, but allowing keys only queries in those cases, but not in others, would be confusing.) """ def __init__(self, bound_queries, orderings): if len(bound_queries) > MAX_ALLOWABLE_QUERIES: raise datastore_errors.BadArgumentError( 'Cannot satisfy query -- too many subqueries (max: %d, got %d).' ' Probable cause: too many IN/!= filters in query.' % (MAX_ALLOWABLE_QUERIES, len(bound_queries))) for query in bound_queries: if query.IsKeysOnly(): raise datastore_errors.BadQueryError( 'MultiQuery does not support keys_only.') self.__bound_queries = bound_queries self.__orderings = orderings def __str__(self): res = 'MultiQuery: ' for query in self.__bound_queries: res = '%s %s' % (res, str(query)) return res def Get(self, limit, offset=0): """Get results of the query with a limit on the number of results. Args: limit: maximum number of values to return. offset: offset requested -- if nonzero, this will override the offset in the original query Returns: A list of entities with at most "limit" entries (less if the query completes before reading limit values). """ count = 1 result = [] iterator = self.Run() try: for i in xrange(offset): val = iterator.next() except StopIteration: pass try: while count <= limit: val = iterator.next() result.append(val) count += 1 except StopIteration: pass return result class SortOrderEntity(object): """Allow entity comparisons using provided orderings. The iterator passed to the constructor is eventually consumed via calls to GetNext(), which generate new SortOrderEntity s with the same orderings. """ def __init__(self, entity_iterator, orderings): """Ctor. Args: entity_iterator: an iterator of entities which will be wrapped. orderings: an iterable of (identifier, order) pairs. order should be either Query.ASCENDING or Query.DESCENDING. """ self.__entity_iterator = entity_iterator self.__entity = None self.__min_max_value_cache = {} try: self.__entity = entity_iterator.next() except StopIteration: pass else: self.__orderings = orderings def __str__(self): return str(self.__entity) def GetEntity(self): """Gets the wrapped entity.""" return self.__entity def GetNext(self): """Wrap and return the next entity. The entity is retrieved from the iterator given at construction time. """ return MultiQuery.SortOrderEntity(self.__entity_iterator, self.__orderings) def CmpProperties(self, that): """Compare two entities and return their relative order. Compares self to that based on the current sort orderings and the key orders between them. Returns negative, 0, or positive depending on whether self is less, equal to, or greater than that. This comparison returns as if all values were to be placed in ascending order (highest value last). Only uses the sort orderings to compare (ignores keys). Args: that: SortOrderEntity Returns: Negative if self < that Zero if self == that Positive if self > that """ if not self.__entity: return cmp(self.__entity, that.__entity) for (identifier, order) in self.__orderings: value1 = self.__GetValueForId(self, identifier, order) value2 = self.__GetValueForId(that, identifier, order) result = cmp(value1, value2) if order == Query.DESCENDING: result = -result if result: return result return 0 def __GetValueForId(self, sort_order_entity, identifier, sort_order): value = _GetPropertyValue(sort_order_entity.__entity, identifier) entity_key = sort_order_entity.__entity.key() if (entity_key, identifier) in self.__min_max_value_cache: value = self.__min_max_value_cache[(entity_key, identifier)] elif isinstance(value, list): if sort_order == Query.DESCENDING: value = min(value) else: value = max(value) self.__min_max_value_cache[(entity_key, identifier)] = value return value def __cmp__(self, that): """Compare self to that w.r.t. values defined in the sort order. Compare an entity with another, using sort-order first, then the key order to break ties. This can be used in a heap to have faster min-value lookup. Args: that: other entity to compare to Returns: negative: if self is less than that in sort order zero: if self is equal to that in sort order positive: if self is greater than that in sort order """ property_compare = self.CmpProperties(that) if property_compare: return property_compare else: return cmp(self.__entity.key(), that.__entity.key()) def Run(self): """Return an iterable output with all results in order.""" results = [] count = 1 log_level = logging.DEBUG - 1 for bound_query in self.__bound_queries: logging.log(log_level, 'Running query #%i' % count) results.append(bound_query.Run()) count += 1 def IterateResults(results): """Iterator function to return all results in sorted order. Iterate over the array of results, yielding the next element, in sorted order. This function is destructive (results will be empty when the operation is complete). Args: results: list of result iterators to merge and iterate through Yields: The next result in sorted order. """ result_heap = [] for result in results: heap_value = MultiQuery.SortOrderEntity(result, self.__orderings) if heap_value.GetEntity(): heapq.heappush(result_heap, heap_value) used_keys = set() while result_heap: top_result = heapq.heappop(result_heap) results_to_push = [] if top_result.GetEntity().key() not in used_keys: yield top_result.GetEntity() else: pass used_keys.add(top_result.GetEntity().key()) results_to_push = [] while result_heap: next = heapq.heappop(result_heap) if cmp(top_result, next): results_to_push.append(next) break else: results_to_push.append(next.GetNext()) results_to_push.append(top_result.GetNext()) for popped_result in results_to_push: if popped_result.GetEntity(): heapq.heappush(result_heap, popped_result) return IterateResults(results) def Count(self, limit=None): """Return the number of matched entities for this query. Will return the de-duplicated count of results. Will call the more efficient Get() function if a limit is given. Args: limit: maximum number of entries to count (for any result > limit, return limit). Returns: count of the number of entries returned. """ if limit is None: count = 0 for i in self.Run(): count += 1 return count else: return len(self.Get(limit)) def __setitem__(self, query_filter, value): """Add a new filter by setting it on all subqueries. If any of the setting operations raise an exception, the ones that succeeded are undone and the exception is propagated upward. Args: query_filter: a string of the form "property operand". value: the value that the given property is compared against. """ saved_items = [] for index, query in enumerate(self.__bound_queries): saved_items.append(query.get(query_filter, None)) try: query[query_filter] = value except: for q, old_value in itertools.izip(self.__bound_queries[:index], saved_items): if old_value is not None: q[query_filter] = old_value else: del q[query_filter] raise def __delitem__(self, query_filter): """Delete a filter by deleting it from all subqueries. If a KeyError is raised during the attempt, it is ignored, unless every subquery raised a KeyError. If any other exception is raised, any deletes will be rolled back. Args: query_filter: the filter to delete. Raises: KeyError: No subquery had an entry containing query_filter. """ subquery_count = len(self.__bound_queries) keyerror_count = 0 saved_items = [] for index, query in enumerate(self.__bound_queries): try: saved_items.append(query.get(query_filter, None)) del query[query_filter] except KeyError: keyerror_count += 1 except: for q, old_value in itertools.izip(self.__bound_queries[:index], saved_items): if old_value is not None: q[query_filter] = old_value raise if keyerror_count == subquery_count: raise KeyError(query_filter) def __iter__(self): return iter(self.__bound_queries) class Iterator(object): """An iterator over the results of a datastore query. Iterators are used to access the results of a Query. An iterator is obtained by building a Query, then calling Run() on it. Iterator implements Python's iterator protocol, so results can be accessed with the for and in statements: > it = Query('Person').Run() > for person in it: > print 'Hi, %s!' % person['name'] """ def __init__(self, cursor, keys_only=False): self.__cursor = cursor self.__buffer = [] self.__more_results = True self.__keys_only = keys_only def _Next(self, count): """Returns the next result(s) of the query. Not intended to be used by application developers. Use the python iterator protocol instead. This method returns the next entities or keys from the list of matching results. If the query specified a sort order, results are returned in that order. Otherwise, the order is undefined. The argument specifies the number of results to return. If it's greater than the number of remaining results, all of the remaining results are returned. In that case, the length of the returned list will be smaller than count. There is an internal buffer for use with the next() method. If this buffer is not empty, up to 'count' values are removed from this buffer and returned. It's best not to mix _Next() and next(). The results are always returned as a list. If there are no results left, an empty list is returned. Args: # the number of results to return; must be >= 1 count: int or long Returns: # a list of entities or keys [Entity or Key, ...] """ if not isinstance(count, (int, long)) or count <= 0: raise datastore_errors.BadArgumentError( 'Argument to _Next must be an int greater than 0; received %s (a %s)' % (count, typename(count))) if self.__buffer: raise datastore_errors.BadRequestError( 'You can\'t mix next() and _Next()') if not self.__more_results: return [] req = datastore_pb.NextRequest() req.set_count(count) req.mutable_cursor().CopyFrom(self._ToPb()) result = datastore_pb.QueryResult() try: apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Next', req, result) except apiproxy_errors.ApplicationError, err: raise _ToDatastoreError(err) self.__more_results = result.more_results() if self.__keys_only: return [Key._FromPb(e.key()) for e in result.result_list()] else: return [Entity._FromPb(e) for e in result.result_list()] _BUFFER_SIZE = 20 def next(self): if not self.__buffer: self.__buffer = self._Next(self._BUFFER_SIZE) try: return self.__buffer.pop(0) except IndexError: raise StopIteration def __iter__(self): return self def _ToPb(self): """Converts this Iterator to its protocol buffer representation. Not intended to be used by application developers. Enforced by hiding the datastore_pb classes. Returns: # the PB representation of this Iterator datastore_pb.Cursor """ pb = datastore_pb.Cursor() pb.set_cursor(self.__cursor) return pb @staticmethod def _FromPb(pb): """Static factory method. Returns the Iterator representation of the given protocol buffer (datastore_pb.QueryResult). Not intended to be used by application developers. Enforced by hiding the datastore_pb classes. Args: pb: datastore_pb.QueryResult Returns: Iterator """ return Iterator(pb.cursor().cursor(), keys_only=pb.keys_only()) class _Transaction(object): """Encapsulates a transaction currently in progress. If we've sent a BeginTransaction call, then handle will be a datastore_pb.Transaction that holds the transaction handle. If we know the entity group for this transaction, it's stored in the entity_group attribute, which is set by RecordModifiedKeys(). modified_keys is a set containing the Keys of all entities modified (ie put or deleted) in this transaction. If an entity is modified more than once, a BadRequestError is raised. """ def __init__(self): """Initializes modified_keys to the empty set.""" self.handle = None self.entity_group = None self.modified_keys = None self.modified_keys = set() def RecordModifiedKeys(self, keys, error_on_repeat=True): """Updates the modified keys seen so far. Also sets entity_group if it hasn't yet been set. If error_on_repeat is True and any of the given keys have already been modified, raises BadRequestError. Args: keys: sequence of Keys """ keys, _ = NormalizeAndTypeCheckKeys(keys) if keys and not self.entity_group: self.entity_group = keys[0].entity_group() keys = set(keys) if error_on_repeat: already_modified = self.modified_keys.intersection(keys) if already_modified: raise datastore_errors.BadRequestError( "Can't update entity more than once in a transaction: %r" % already_modified.pop()) self.modified_keys.update(keys) def RunInTransaction(function, *args, **kwargs): """Runs a function inside a datastore transaction. Runs the user-provided function inside transaction, retries default number of times. Args: # a function to be run inside the transaction function: callable # positional arguments to pass to the function args: variable number of any type Returns: the function's return value, if any Raises: TransactionFailedError, if the transaction could not be committed. """ return RunInTransactionCustomRetries( DEFAULT_TRANSACTION_RETRIES, function, *args, **kwargs) def RunInTransactionCustomRetries(retries, function, *args, **kwargs): """Runs a function inside a datastore transaction. Runs the user-provided function inside a full-featured, ACID datastore transaction. Every Put, Get, and Delete call in the function is made within the transaction. All entities involved in these calls must belong to the same entity group. Queries are not supported. The trailing arguments are passed to the function as positional arguments. If the function returns a value, that value will be returned by RunInTransaction. Otherwise, it will return None. The function may raise any exception to roll back the transaction instead of committing it. If this happens, the transaction will be rolled back and the exception will be re-raised up to RunInTransaction's caller. If you want to roll back intentionally, but don't have an appropriate exception to raise, you can raise an instance of datastore_errors.Rollback. It will cause a rollback, but will *not* be re-raised up to the caller. The function may be run more than once, so it should be idempotent. It should avoid side effects, and it shouldn't have *any* side effects that aren't safe to occur multiple times. This includes modifying the arguments, since they persist across invocations of the function. However, this doesn't include Put, Get, and Delete calls, of course. Example usage: > def decrement(key, amount=1): > counter = datastore.Get(key) > counter['count'] -= amount > if counter['count'] < 0: # don't let the counter go negative > raise datastore_errors.Rollback() > datastore.Put(counter) > > counter = datastore.Query('Counter', {'name': 'foo'}) > datastore.RunInTransaction(decrement, counter.key(), amount=5) Transactions satisfy the traditional ACID properties. They are: - Atomic. All of a transaction's operations are executed or none of them are. - Consistent. The datastore's state is consistent before and after a transaction, whether it committed or rolled back. Invariants such as "every entity has a primary key" are preserved. - Isolated. Transactions operate on a snapshot of the datastore. Other datastore operations do not see intermediated effects of the transaction; they only see its effects after it has committed. - Durable. On commit, all writes are persisted to the datastore. Nested transactions are not supported. Args: # number of retries retries: integer # a function to be run inside the transaction function: callable # positional arguments to pass to the function args: variable number of any type Returns: the function's return value, if any Raises: TransactionFailedError, if the transaction could not be committed. """ if _CurrentTransactionKey(): raise datastore_errors.BadRequestError( 'Nested transactions are not supported.') if retries < 0: raise datastore_errors.BadRequestError( 'Number of retries should be non-negative number.') tx_key = None try: tx_key = _NewTransactionKey() tx = _Transaction() _txes[tx_key] = tx for i in range(0, retries + 1): tx.modified_keys.clear() try: result = function(*args, **kwargs) except: original_exception = sys.exc_info() if tx.handle: try: resp = api_base_pb.VoidProto() apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Rollback', tx.handle, resp) except: exc_info = sys.exc_info() logging.info('Exception sending Rollback:\n' + ''.join(traceback.format_exception(*exc_info))) type, value, trace = original_exception if type is datastore_errors.Rollback: return else: raise type, value, trace if tx.handle: try: resp = datastore_pb.CommitResponse() apiproxy_stub_map.MakeSyncCall('datastore_v3', 'Commit', tx.handle, resp) except apiproxy_errors.ApplicationError, err: if (err.application_error == datastore_pb.Error.CONCURRENT_TRANSACTION): logging.warning('Transaction collision for entity group with ' 'key %r. Retrying...', tx.entity_group) tx.handle = None tx.entity_group = None continue else: raise _ToDatastoreError(err) return result raise datastore_errors.TransactionFailedError( 'The transaction could not be committed. Please try again.') finally: if tx_key in _txes: del _txes[tx_key] del tx_key def _MaybeSetupTransaction(request, keys): """Begins a transaction, if necessary, and populates it in the request. If we're currently inside a transaction, this records the entity group, checks that the keys are all in that entity group, creates the transaction PB, and sends the BeginTransaction. It then populates the transaction handle in the request. Raises BadRequestError if the entity has a different entity group than the current transaction. Args: request: GetRequest, PutRequest, or DeleteRequest keys: sequence of Keys Returns: _Transaction if we're inside a transaction, otherwise None """ assert isinstance(request, (datastore_pb.GetRequest, datastore_pb.PutRequest, datastore_pb.DeleteRequest)) tx_key = None try: tx_key = _CurrentTransactionKey() if tx_key: tx = _txes[tx_key] groups = [k.entity_group() for k in keys] if tx.entity_group: expected_group = tx.entity_group else: expected_group = groups[0] for group in groups: if (group != expected_group or (not group.has_id_or_name() and group is not expected_group)): raise _DifferentEntityGroupError(expected_group, group) if not tx.handle: tx.handle = datastore_pb.Transaction() req = api_base_pb.VoidProto() apiproxy_stub_map.MakeSyncCall('datastore_v3', 'BeginTransaction', req, tx.handle) request.mutable_transaction().CopyFrom(tx.handle) return tx finally: del tx_key def _DifferentEntityGroupError(a, b): """Raises a BadRequestError that says the given entity groups are different. Includes the two entity groups in the message, formatted more clearly and concisely than repr(Key). Args: a, b are both Keys that represent entity groups. """ def id_or_name(key): if key.name(): return 'name=%r' % key.name() else: return 'id=%r' % key.id() raise datastore_errors.BadRequestError( 'Cannot operate on different entity groups in a transaction: ' '(kind=%r, %s) and (kind=%r, %s).' % (a.kind(), id_or_name(a), b.kind(), id_or_name(b))) def _FindTransactionFrameInStack(): """Walks the stack to find a RunInTransaction() call. Returns: # this is the RunInTransactionCustomRetries() frame record, if found frame record or None """ frame = sys._getframe() filename = frame.f_code.co_filename frame = frame.f_back.f_back while frame: if (frame.f_code.co_filename == filename and frame.f_code.co_name == 'RunInTransactionCustomRetries'): return frame frame = frame.f_back return None _CurrentTransactionKey = _FindTransactionFrameInStack _NewTransactionKey = sys._getframe def _GetCompleteKeyOrError(arg): """Expects an Entity or a Key, and returns the corresponding Key. Raises BadArgumentError or BadKeyError if arg is a different type or is incomplete. Args: arg: Entity or Key Returns: Key """ if isinstance(arg, Key): key = arg elif isinstance(arg, basestring): key = Key(arg) elif isinstance(arg, Entity): key = arg.key() elif not isinstance(arg, Key): raise datastore_errors.BadArgumentError( 'Expects argument to be an Entity or Key; received %s (a %s).' % (arg, typename(arg))) assert isinstance(key, Key) if not key.has_id_or_name(): raise datastore_errors.BadKeyError('Key %r is not complete.' % key) return key def _GetPropertyValue(entity, property): """Returns an entity's value for a given property name. Handles special properties like __key__ as well as normal properties. Args: entity: datastore.Entity property: str; the property name Returns: property value. For __key__, a datastore_types.Key. Raises: KeyError, if the entity does not have the given property. """ if property in datastore_types._SPECIAL_PROPERTIES: assert property == datastore_types._KEY_SPECIAL_PROPERTY return entity.key() else: return entity[property] def _AddOrAppend(dictionary, key, value): """Adds the value to the existing values in the dictionary, if any. If dictionary[key] doesn't exist, sets dictionary[key] to value. If dictionary[key] is not a list, sets dictionary[key] to [old_value, value]. If dictionary[key] is a list, appends value to that list. Args: dictionary: a dict key, value: anything """ if key in dictionary: existing_value = dictionary[key] if isinstance(existing_value, list): existing_value.append(value) else: dictionary[key] = [existing_value, value] else: dictionary[key] = value def _ToDatastoreError(err): """Converts an apiproxy.ApplicationError to an error in datastore_errors. Args: err: apiproxy.ApplicationError Returns: a subclass of datastore_errors.Error """ errors = { datastore_pb.Error.BAD_REQUEST: datastore_errors.BadRequestError, datastore_pb.Error.CONCURRENT_TRANSACTION: datastore_errors.TransactionFailedError, datastore_pb.Error.INTERNAL_ERROR: datastore_errors.InternalError, datastore_pb.Error.NEED_INDEX: datastore_errors.NeedIndexError, datastore_pb.Error.TIMEOUT: datastore_errors.Timeout, } if err.application_error in errors: raise errors[err.application_error](err.error_detail) else: raise datastore_errors.Error(err.error_detail)