Gregg Lind wrote:
>
> I use declarative base for defining classes.
>
> I have a constraint that only works in Postgres. How do I declare
> that constraint "lowername_check" only if the session is going
> postgres (and not to sqlite, for example).
>
> pg_only_constraint = CheckConstraint("lowername !~
> '[[:upper:]]'",name='lowername_check'),
> class Data(Base):
> __tablename__ = 'Data'
> lowername=Column(Unicode, nullable=False)
> __table_args__ = (
> pg_only_constraint, {}
> )
The cleanest way is to use the schema.DDL() construct which can filter
against various backends, but requires that you spell out the constraint
explicitly:
DDL("CREATE CONSTRAINT ....", on="postgres").execute_at('after-create',
Data.__table__)
Alternatively, if you want to stick with the CheckConstraint object you
can create a function "create_pg_constraints()" which is called at the
point your app calls "create_engine()", that contains all PG specific
constructs - the function would be called based on engine.dialect.name ==
"postgres".
We have a more flexible architecture in 0.6 for this sort of thing and I
think if we add an AddConstraint() construct there and also move most of
DDL()'s execute-at and "on" functionality into the base DDLElement class,
that would enable both constructs to be combined together as in
AddConstraint(CheckConstraint(...args...),
on="postgres")).execute_at('after-create', Data.__table__).
>
>
> Thanks!
>
> Gregg Lind
>
> >
>
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