Question

I have tables like this:

from sqlalchemy import Column, Integer, select
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class Blah(Base):
    __tablename__ = 'Blah'
    container_id = Column(Integer, primary_key=True)
    blah_id = Column(Integer, primary_key=True)
    gprop = Column(Integer, index=True, nullable=False)

class GProp(Base):
    __table__ = select([
        Blah.container_id, Blah.gprop
    ]).group_by(
        Blah.container_id, Blah.gprop
    ).alias()

As it is GProp.__table__.primary_key picks up the container_id column, but I can’t find a way to make the gprop column part of the primary key. This breaks my queries, SQLAlchemy will only load one GProp per container.

Unsuccessful fixes so far: Adding Column attributes is forbidden because it redefines existing columns, adding a PrimaryKeyConstraint to __table_args__ has no effect, and monkey-patching __table__.primary_key gets caught by just the wrong assertion.

Answer 1

OK, adding

__mapper_args__ = dict(primary_key=[__table__.c.container_id, __table__.c.gprop])

does the job, even though it isn’t reflected on __table__.primary_key.