On Sep 28, 2012, at 11:15 AM, Alex D. wrote:
> Is there a good way to have a dialect automatically add casting to 'THEN'
> expressions in 'CASE' statements?
>
> I'm working on a dialect for the H2 database, via Jython. H2 requires values
> in a 'THEN' expression to have explicit casts (see: Unknown data type thrown
> with a case statement where all values are parameters in preparedStatement )
>
> I would like to make it so that my H2 dialect will automatically add casting
> to 'CASE' expressions, so that users of the dialect don't have to use
> literal_columns each time they want to use a 'CASE' expression.
>
> One idea I had was to add a 'before_execute' event that checks elements to
> see if their case statements, but that seems a bit kludgy. is there a better
> way?
if you're writing a dialect, then you're in control of everything to do with
rendering SQL and there's no need to consider the usual event hooks. In this
case you'd look to override visit_case() in your compiler class. Below is a
pseudo-approach for how to rewrite the case() with the cast() expressions
inside of it:
class MyCompiler(Compiler):
def visit_case(self, clause, **kwargs):
adjusted = case(
whens=[(wh, cast(res, String)) for wh, res in
clause.whens,
else_ = ...
)
return super(MyCompiler, self).visit_case(adjusted, **kwargs)
>
>
> Levity:
> Q: What do a database developer and a hollywood producer have in common?
> A: They both can have problems with casting.
>
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