Hi Patrick,
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.
Regards,
Richard
From: Fabio Maulo
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
