[ZODB-Dev] AdaptableStorage and OR mapping strategy (was: AdaptableStorage and ZClass instances)

[Shane Hathaway]

Roch=E9 Compaan wrote:
> I have started rewriting SQLGatewayBase to do more work. So far it's
> going well but I wanted to bounce some ideas off you wrt the state that
> the load method should return.
>=20
> Here's my thinking at the moment:
>=20
>     If the schema is of type FieldSchema then the state returned should
>     be a single value eg.:
>=20
>         items =3D self.execute(self.readsql(key))
>         if items:
>             state =3D items[0][0]
>         else:
>             state =3D ''
>         return state, state
>=20
>     If the schema is of type RowSchema then the state returned should b=
e
>     a sequence and we assert that a single row is returned:
>=20
>         items =3D self.execute(self.readsql(key))
>         if items:
>             assert len(items) =3D 1
>             state =3D items[0]
>         else:
>             state =3D ''
>         return state, state
>=20
>     If the schema is of type RowSequenceSchema then the state returned
>     should be a sequence:
>=20
>         items =3D self.execute(self.readsql(key))
>         if items:
>             state =3D items
>             # to ensure a hash of the state stays the same
>             state.sort()
>         else:
>             state =3D []
>         return state, tuple(state)

Right on.  In the last case, it returns a sequence of tuples.  The=20
store() method follows the same rules.

> If a subclass needs to do something special when computing state it can
> simply override the load method.

Right.

I originally decided that all gateways would load and store tuples of=20
tuples, but that quickly became cumbersome and error-prone.  So although=20
you now have to code for three cases instead of one, it's worth the=20
complexity. :-)

Shane