[odb-users] "Dynamic" joins in views

[Nicolas ALBEZA]

I managed to rewrite the query using C++-integrated queries, and it's
working like a charm.

Many thanks !

Le 1 mars 2012 10:05, Boris Kolpackov <boris at codesynthesis.com> a écrit :

> Hi Nicolas,
>
> Nicolas ALBEZA <n.albeza at gmail.com> writes:
>
> > I was wondering if it was possible to do "dynamic" joins in views, for
> > example, to be able to specify a join condition at runtime, without using
> > native queries.
>
> Hm, you could try providing a native predicate that includes a reference
> to a global (or class-static, or even a TLS, if your compiler supports
> this mechanism) variable:
>
> extern int param;
>
> #pragma db view \
>  object(t1)    \
>  object(t2: "t1.id = t2.t1_id AND t2.t3_id =" + odb::query<view>::_ref
> (param))
> struct view
> {
>  ...
> };
>
> > Result SQL query example:
> >
> > select field from t1 left join t2 on (t1.id = t2.t1_id && t2.t3_id =
> > <dynamic value, eg: 42>);
>
> Isn't this equivalent to:
>
> select field from t1 left join t2 on t1.id = t2.t1_id where t2.t3_id = ?
>
> If you can rewrite the query like this, then you don't need any of the
> above and can use C++-integrated queries.
>
> Boris
>



-- 
ALBEZA "Pause" Nicolas