the issue is, the "deferrable" flag on FK generates the keyword on SQLite
during DDL and is not accepted by SQLite ? seems like we'd just get the SQLite
dialect to not render that keyword (i.e. should be core behavior). Also as a
workaround you could possibly use a @compiles("sqlite") on CreateConstraint...
(I seem to have missed this thread early on sorry for that !)
On Sep 27, 2011, at 6:04 PM, Wichert Akkerman wrote:
> I hate to do this kind of thing, but I haven't gotten any feedback on this
> and I would love to hear some feedback/opinions. How do other people handle
> deferrable constraints?
>
>
> On 2011-9-14 13:59, Wichert Akkerman wrote:
>> On 09/14/2011 12:25 PM, Wichert Akkerman wrote:
>>> Constraints marked as deferrable result in a syntax error when using
>>> SQLite. Is this deliberate, or a bug in the sqlite dialect?
>>
>> As a workaround I figured I could use events to only add deferrable
>> constraint variants on PostgreSQL and use the non-deferrable version on
>> other database. That resulted in this code:
>>
>> _generic_constraints = [UniqueConstraint('article_id', 'colour, 'size')]
>> _ deferrable_variant_constraints = [
>> UniqueConstraint('article_id', 'uuid', deferrable=True,
>> initially='DEFERRED'),
>> ]
>>
>> class Article(BaseObject):
>> __table_args = (_generic_constraints[0], _deferrable_constraints[0], {})
>>
>> def deferrable_supported(ddl, target, bind, **kw):
>> """Check if deferrable constraints are supported.
>>
>> This function can be used as a callable for
>> :ref:`execute_if<sqlalchemy:sqlalchemy.schema.DDLElement.execute_if>` to
>> only run DDL statements on databases that support deferrable constraints.
>> """
>> return bind.dialect == 'postgresql'
>>
>>
>> def deferrable_not_supported(ddl, target, bind, **kw):
>> """Check if deferrable constraints are not supported.
>>
>> This function can be used as a callable for
>> :ref:`execute_if<sqlalchemy:sqlalchemy.schema.DDLElement.execute_if>` to
>> only run DDL statements on databases that do not support deferrable
>> constraints.
>> """
>> return not deferrable_supported(ddl, target, bind, **kw)
>>
>> for constraint in _generic_variant_constraints:
>> listen(Article.__table__, 'after_create',
>> AddConstraint(constraint)
>> .execute_if(callable_=deferrable_not_supported))
>>
>> for constraint in _deferrable_variant_constraints:
>> listen(Article.__table__, 'after_create',
>> AddConstraint(constraint)
>> .execute_if(callable_=deferrable_supported))
>>
>>
>>
>> But this fails as well since SQLite does not support ALTER TABLE .. ADD
>> CONSTRAINT. Is there another way to create deferrable constraints only
>> on databases that support it?
>>
>> Wichert.
>>
>>
>>
>
>
> --
> Wichert Akkerman <[email protected]> It is simple to make things.
> http://www.wiggy.net/ It is hard to make things simple.
>
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