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How to use shard_id method in localstack

Best Python code snippet using localstack_python

horizontal_shard.py

Source:horizontal_shard.py

1# ext/horizontal_shard.py2# Copyright (C) 2005-2017 the SQLAlchemy authors and contributors3# <see AUTHORS file>4#5# This module is part of SQLAlchemy and is released under6# the MIT License: http://www.opensource.org/licenses/mit-license.php7"""Horizontal sharding support.8Defines a rudimental 'horizontal sharding' system which allows a Session to9distribute queries and persistence operations across multiple databases.10For a usage example, see the :ref:`examples_sharding` example included in11the source distribution.12"""13from .. import util14from ..orm.session import Session15from ..orm.query import Query16__all__ = ['ShardedSession', 'ShardedQuery']17class ShardedQuery(Query):18    def __init__(self, *args, **kwargs):19        super(ShardedQuery, self).__init__(*args, **kwargs)20        self.id_chooser = self.session.id_chooser21        self.query_chooser = self.session.query_chooser22        self._shard_id = None23    def set_shard(self, shard_id):24        """return a new query, limited to a single shard ID.25        all subsequent operations with the returned query will26        be against the single shard regardless of other state.27        """28        q = self._clone()29        q._shard_id = shard_id30        return q31    def _execute_and_instances(self, context):32        def iter_for_shard(shard_id):33            context.attributes['shard_id'] = shard_id34            result = self._connection_from_session(35                mapper=self._mapper_zero(),36                shard_id=shard_id).execute(37                context.statement,38                self._params)39            return self.instances(result, context)40        if self._shard_id is not None:41            return iter_for_shard(self._shard_id)42        else:43            partial = []44            for shard_id in self.query_chooser(self):45                partial.extend(iter_for_shard(shard_id))46            # if some kind of in memory 'sorting'47            # were done, this is where it would happen48            return iter(partial)49    def _get_impl(self, ident, fallback_fn):50        def _fallback(query, ident):51            if self._shard_id is not None:52                return fallback_fn(self, ident)53            else:54                ident = util.to_list(ident)55                for shard_id in self.id_chooser(self, ident):56                    q = self.set_shard(shard_id)57                    o = fallback_fn(q, ident)58                    if o is not None:59                        return o60                else:61                    return None62        return super(ShardedQuery, self)._get_impl(ident, _fallback)63class ShardedSession(Session):64    def __init__(self, shard_chooser, id_chooser, query_chooser, shards=None,65                 query_cls=ShardedQuery, **kwargs):66        """Construct a ShardedSession.67        :param shard_chooser: A callable which, passed a Mapper, a mapped68          instance, and possibly a SQL clause, returns a shard ID.  This id69          may be based off of the attributes present within the object, or on70          some round-robin scheme. If the scheme is based on a selection, it71          should set whatever state on the instance to mark it in the future as72          participating in that shard.73        :param id_chooser: A callable, passed a query and a tuple of identity74          values, which should return a list of shard ids where the ID might75          reside.  The databases will be queried in the order of this listing.76        :param query_chooser: For a given Query, returns the list of shard_ids77          where the query should be issued.  Results from all shards returned78          will be combined together into a single listing.79        :param shards: A dictionary of string shard names80          to :class:`~sqlalchemy.engine.Engine` objects.81        """82        super(ShardedSession, self).__init__(query_cls=query_cls, **kwargs)83        self.shard_chooser = shard_chooser84        self.id_chooser = id_chooser85        self.query_chooser = query_chooser86        self.__binds = {}87        self.connection_callable = self.connection88        if shards is not None:89            for k in shards:90                self.bind_shard(k, shards[k])91    def connection(self, mapper=None, instance=None, shard_id=None, **kwargs):92        if shard_id is None:93            shard_id = self.shard_chooser(mapper, instance)94        if self.transaction is not None:95            return self.transaction.connection(mapper, shard_id=shard_id)96        else:97            return self.get_bind(98                mapper,99                shard_id=shard_id,100                instance=instance101            ).contextual_connect(**kwargs)102    def get_bind(self, mapper, shard_id=None,103                 instance=None, clause=None, **kw):104        if shard_id is None:105            shard_id = self.shard_chooser(mapper, instance, clause=clause)106        return self.__binds[shard_id]107    def bind_shard(self, shard_id, bind):...

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