As always, thank you for the complete, exhaustive answer. This
particular thing is definitely and edge case, and rather non-obvious,
so thank you for walking me through it.
Either of those are clean enough for me!
Is there are more proper / general way to describe the problem, so
google and make this answer easier to find?
Gregg
On Fri, May 29, 2009 at 12:10 PM, Michael Bayer
<mike...@zzzcomputing.com> wrote:
>
> 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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