> I think the original intention for ISQLFunction was to call (dialect-
> specific) user-defined functions (hence the name), not to create arbitrary
> snippets of SQL. Since the implementation has used positional parameters
I
> don't think you can generate the SQL you're wanting.
>
> I think the two options you suggested are viable: Create a new
> interface/implementation that allows arbitrary hand-cut SQL from a
parameter
> list, or change the current implementation to use named parameters (which
> would only be needed in this specific case, and we'd need to be careful to
> generate a unique parameter name for each instance of the function call
> within a single query). Either one could be added to JIRA as a potential
> improvement.
>
> I'm guessing (but I haven't tried it) that a simpler option might be to
just
> render the actual parameter values into the SQL string (i.e., not
> parameterised). Notwithstanding that the simplest option, if it's open to
> you, is to create a user-defined function in the database that you can
call.
One solution could be similar to what console.writeline does and
what I do in my framework as well: use {} placeholders. So if someone wants
to call a function Foo(@a, @b), they specify the function as Foo({0}, {1}),
and the function definition object has besides this string also a list of
objects, which are transformed into parameters or pieces of this string
(e.g. values, another function, etc.).
This way, the dialect or at least the part where db specific
parameters are created, can deal with the parameter creation by transforming
the list of objects in the function definition object to parameters or
snippets, place them back in the list of objects and a generic piece of code
can then transform the function definition object to a SQL snippet. So if
you have to re-use a parameter: "FooBar({0}, {1}) <> {0}", you can.
This system is also usable for creating case statements and for
example function mappings in linq.
FB
>
> Regards,
> Richard
>
>
> From: Fabio Maulo <mailto:[email protected]>
> Sent: Sunday, August 29, 2010 5:05 AM
> To: [email protected]
> Subject: Re: [nhibernate-development] Re: ISQLFunction with Repeated
> Arguments
>
> Which is the problem you have found implementing
> NullSafeEquals(p1,p2) ?
>
>
> On Sat, Aug 28, 2010 at 6:13 PM, Patrick Earl <[email protected]>
> wrote:
>
>
> Thanks for your feedback Fabio. The function would be
similar
> to
> EqOrNullExpression but would offer the following additional
> functionality:
>
> 1. It would work for database columns and subselects as
well,
> not
> just parameters passed from .NET.
> 3. The HQL function would make the code easy to read and
> eliminate
> the possibility of error in this area where errors are
common.
> 2. The function could easily be mapped from a LINQ method
> call.
>
> For example, NullSafeEquals(x.Prop1, x.Prop2). I see that a
> method
> similar to EqOrNullExpression could be implemented to
provide
> support
> for comparing projections in the criteria API. However, my
> immediate
> problem was HQL based, and I would like this to be solvable
> with LINQ
> as well. Alternatives include implementing something like
"IS
> DISTINCT FROM" as a built-in HQL operation and then having a
> LINQ
> method map to that type of node. The dialect would then
> specifically
> handle the SQL implementation using the SQL-99 IS [NOT]
> DISTINCT FROM,
> MySQL <=>, or the complicated clause as needed.
>
> Patrick Earl
>
>
> On Aug 28, 1:13 pm, Fabio Maulo <[email protected]>
wrote:
> > Personally I didn't understand which is the function you
are
> needing.
> > Can you explain a usecase ?
> >
> > In criteria base queries with a property compared to a
> parameter that
> > function is unneeded... perhaps you are thinking something
> else than
> > EqOrNullExpression... I'll wait your explication.
> >
> >
> >
> >
> >
>
> > On Sat, Aug 28, 2010 at 4:02 PM, Patrick Earl
> <[email protected]> wrote:
> > > Solution #1 (duplicate positional parameters based on
> template
> > > contents) looks to be somewhat complicated to implement.
> > > Solution #2 (manipulate HQL AST and parameter list)
> doesn't work for
> > > ICriteria / QueryOver.
> > > Solution #3 (replace positional parameters with named)
> seems
> > > potentially viable.
> >
> > > I have two "big" questions:
> >
> > > 1. Are there cases where positional parameters are
> required, or is it
> > > reasonable to always pre-process positional parameters
> into named
> > > parameters? Along with this, what kind of parameters do
> the criteria
> > > API and Linq generate? Are they always named
parameters?
> > > 2. Why is it required that the type of a null parameter
> is known. In
> > > other words, why is it necessary to call SetParameter
with
> a type
> > > overload? Is there any way to say "put NULL in the DB
> query and
> > > disregard the type?"
> >
> > > I'll do some digging, but if anyone knows this stuff
off-
> hand, that'd
> > > be great to know.
> >
> > > Patrick Earl
> >
> > > On Aug 28, 2:55 am, Patrick Earl <[email protected]>
wrote:
> > > > I'm interested in implementing a function to duplicate
> the behavior of
> > > > "IS NOT DISTINCT FROM" on SQL Server. On PostgreSQL,
> I'd simply use ?
> > > > 1 IS NOT DISTINCT FROM ?2 as the function template.
On
> SQL Server
> > > > though, the template involves repeating the same
> argument: (?1 IS NULL
> > > > AND ?2 IS NULL) OR (?1 IS NOT NULL AND ?2 IS NOT NULL
> AND ?1 = ?2)
> >
> > > > Unfortunately, when used with positional parameters,
the
> function
> > > > template is not processed correctly. The system
> duplicates the ?
> > > > within the query, but it doesn't add another copy of
the
> parameter to
> > > > the parameter list. Here are some possible techniques
> for dealing
> > > > with this issue:
> >
> > > > 1. Create another interface like
> ISQLParameterizedFunction that
> > > > allows modification of the parameter list as well.
> > > > 2. Allow dialects to access the HQL AST and parameter
> list and modify
> > > > them directly.
> > > > 3. Replace the positional parameters with named
> parameters.
> >
> > > > Sadly, I'm too tired for my brain to work properly. I
> just wanted to
> > > > get these thoughts out there to see if anyone had any
> feedback or work-
> > > > arounds.
> >
> > > > Patrick Earl
> >
> > --
> > Fabio Maulo
>
>
>
>
> --
> Fabio Maulo
>
>
