Thomas Farvour Thomas Farvour - 1 month ago 17
Python Question

Using a different schema for the same declarative Base in sqlalchemy

I am new to both Pyramid and SQLAlchemy. I am working on a Python Pyramid project with SQLAlchemy. I have a simple model set up below. How would I go about being able to use this with different schemas at run-time? This will be a PostgreSQL database backend. Right now, "public" is hard-coded into the declarative base model. I would need the ability to use this same model with different schema. What is the best approach? Unless I missed it, the documentation at SQLAlchemy seemed unclear to me.

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, BigInteger

__all__ = [
"LoadTender"
]
__all__.sort()

Base = declarative_base()


class LoadTender(Base):
__tablename__ = "load_tenders"
__table_args__ = {"schema": "public"}

id = Column("pkey", BigInteger, primary_key=True)

def __repr__(self):
return "" % self.id


EDIT: I have appeared to solve my issue, I am updating the snippet to show what I did below.

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, BigInteger

__all__ = [
"LoadTender"
]
__all__.sort()

Base = declarative_base()

class ClientMixin(object):
__table_args__ = {"schema": "client_schema_name"}


class LoadTenderMixin(object):
__tablename__ = "load_tenders"

id = Column("pkey", BigInteger, primary_key=True)

def __repr__(self):
return "" % self.id


class ClientLoadTender(LoadTenderMixin, ClientMixin, Base):
pass

Answer

I think you need a different model for each schema. __abstract__ can make this less painful. This follows on to Paul Yin's answer...

  1. Define an __abstract__ LoadTender model, so you don't have to keep coding it.

    #base.py
    class LoadTender(Base):
        __abstract__ = True
        id = ...
        def __repr__ ...
    
  2. Put a schema-specific Base in the hierarchy for each schema.

    #schema1.py
    from base import LoadTender
    
    PublicBase = declarative_base(metadata=MetaData(schema='public'))
    
    class LoadTender(PublicBase, LoadTender):
        __tablename__ = 'load_tenders'
    
  3. Do the same for other schema.

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