Declarative style for ObsRawNativeFlags and ObsRawPCICFlags

[rod-glover]

We'd like declare ObsRawNativeFlags and ObsRawPCICFlags in declarative base (class) style, as below.

If we do so withprimary_key=True, some tests error out (specifically, but I suspect not only, tests/alembic_migrations/versions/v_7a3b247c577b_add_varsperhistory_native_matview/test_matview.py::test_vars_content).

If we omit primary_key, then SQLAlchemy objects that it cannot determine primary key columns for the table, which is hardly surprising.

Figure out what is going on here and fix it.

Question: Why is it OK to declare a table without primary keys using a functional X = Table(...) declaration, and not using class X?

class ObsRawNativeFlags(Base):
    """Association table for Obs *--* NativeFLag"""
    __tablename__ = "obs_raw_native_flags"

    obs_raw_id = Column(
        BigInteger,
        ForeignKey("obs_raw.obs_raw_id"),
        # primary_key=True,
    )
    native_flag_id = Column(
        Integer,
        ForeignKey("meta_native_flag.native_flag_id"),
        # primary_key=True,
    )

    # Constraints
    obs_raw_native_flag_unique = UniqueConstraint(
        'obs_raw_id', 'native_flag_id', name='obs_raw_native_flag_unique'
    )

Index("flag_index", "obs_raw_id")


class ObsRawPCICFlags(Base):
    """Association table for Obs *--* PCICFLag"""
    __tablename__ = 'obs_raw_pcic_flags'

    obs_raw_id = Column(
        BigInteger,
        ForeignKey('obs_raw.obs_raw_id'),
        # primary_key=True,
    )
    pcic_flag_id = Column(
        Integer,
        ForeignKey('meta_pcic_flag.pcic_flag_id'),
        # primary_key=True,
    )

    # Constraints
    obs_raw_pcic_flag_unique = UniqueConstraint(
        'obs_raw_id', 'pcic_flag_id', name='obs_raw_pcic_flag_unique'
    )


Index('pcic_flag_index', 'obs_raw_id')

[rod-glover]

A possible aid: An SO reply mentions that:

If the table already exist you can reference to the fields directly:

class Humans(Base):
    __table__ = people_table
    id = people_table.c.PeopleID
    name = people_table.c.PeopleName

In the absence of a better solution, this may give us a way to at least give the effect of a declarative style, whilst retaining the Table definitions. Benefit: Code completion will work better. Nada más.

[rod-glover]

It may also be possible to avoid the problem by creating the FK constraint outside of the table.