python - SQLAlchemy Classical Mapping Model to sharded Postgres databases -

the situation:

i have set of 12 tables (representing data month) sharded across 6 databases. need sample set of data across of these databases given month.

why used classical mappping model rather declarative model:

i require access 1 of 12 types of table gathering sample of data single given month each time code run. classical mapping model allows me dynamically define table name want map @ run time, rather create mappings 12 tables across 6 databases believe required declarative.

the problem:

i trying follow entity_name example given here mapping month data class each of tables given month on 6 different databases.

but getting unmappedclasserror stating base class, new classes derived from, 'is not mapped'.

so on trying initialise 1 of new mapped tables type: <class '__main__.db1month1'> reporting unmappedclasserror: class 'audit.db.orm.mappedclasses.monthdata' not mapped.

any ideas?

if needed can paste in code here i'm worried it's little long. using map_class_to_some_table method defined in entity_name example mappings , haven't altered it.

ended scrapping , following this shardedsession example instead.

my final class looks this:

class shardsessionmanager(object):      def __init__(self, month):         self.month = month          #step1: database engines         self.engines = {}         name, db in shard_dbs.iteritems():             self.engines[name] = create_engine('postgresql+psycopg2://', creator=db.get_connection, client_encoding='utf8')          #step2: create session function - bind shard ids databases within shardedsession         self.create_session = sessionmaker(class_=shardedsession)         self.create_session.configure(shards=self.engines,                                       shard_chooser=self.shard_chooser,                                        id_chooser=self.id_chooser,                                        query_chooser=self.query_chooser)         #step3: table setup         self._make_tables(self.month)          #step4: map classes         self._map_tables()      @staticmethod     def shard_chooser(mapper, instance, clause=none):         if isinstance(instance, datatable):             return id_chooser(instance.brand_id)      @staticmethod     def id_chooser(data_id):         ...      @staticmethod     def query_chooser(query):         ...      def _make_tables(self, month):         self.meta = metadata()         self.data_table = datatable(month, self.meta).table          ... other tables ...      def _map_tables(self):         try:             mapper(datatable, self.data_table,                     properties={ ... })             ...      def get_random_data(self, parent_id):         session = self.create_session()         return session.query(datatable).filter(...