class Entity1(Base):
  __tablename__ = 'entity1' ## I tried combination of <db>.<table> with no success
  entity1_id = Column(Integer, primary_key=True)
  entity2_id = Column(Integer, ForeignKey('db2.entity2.entity2_id'))
  entity2 = relationship('Entity2')

class Entity2(Base):
  __tablename__ = 'entity2' ## I tried combination of <db>.<table> with no success
  entity2_id = Column(Integer, primary_key=True)

class Entity2(Base):
    __tablename__ = 'entity2' ## I tried combination of <db>.<table> with no success
    __table_args__ = {'schema': 'db2'}
    entity2_id = Column(Integer, primary_key=True)

class Entity1(Base):
    __tablename__ = 'entity1' ## I tried combination of <db>.<table> with no success
    __table_args__ = {'schema': 'db1'}
    entity1_id = Column(Integer, primary_key=True)
    entity2_id = Column(Integer, ForeignKey(Entity2.entity2_id))
    entity2 = relationship('Entity2')