API Documentation¶

class sqlalchemy.ext.horizontal_shard.ShardedSession(shard_chooser, id_chooser, query_chooser, shards=None, query_cls=<class 'sqlalchemy.ext.horizontal_shard.ShardedQuery'>, **kwargs)¶

__init__(shard_chooser, id_chooser, query_chooser, shards=None, query_cls=<class 'sqlalchemy.ext.horizontal_shard.ShardedQuery'>, **kwargs)¶

Construct a ShardedSession.

Parameters:

shard_chooser – A callable which, passed a Mapper, a mapped instance, and possibly a SQL clause, returns a shard ID. This id may be based off of the attributes present within the object, or on some round-robin scheme. If the scheme is based on a selection, it should set whatever state on the instance to mark it in the future as participating in that shard. id_chooser – A callable, passed a query and a tuple of identity values, which should return a list of shard ids where the ID might reside. The databases will be queried in the order of this listing. query_chooser – For a given Query, returns the list of shard_ids where the query should be issued. Results from all shards returned will be combined together into a single listing. shards – A dictionary of string shard names to Engine objects.

class sqlalchemy.ext.horizontal_shard.ShardedQuery(*args, **kwargs)¶

set_shard(shard_id)¶

return a new query, limited to a single shard ID.

all subsequent operations with the returned query will be against the single shard regardless of other state.