[Dbix-class] A more accurate redux of zby's comments

[Matt S Trout]

On Fri, Jan 25, 2008 at 10:10:45AM +0100, Zbigniew Lukasiak wrote:
> On Jan 25, 2008 8:07 AM, Matt S Trout <dbix-class at trout.me.uk> wrote:
> > >  what would that
> > > 'proceed as normal' mean? Would it mean that the uniqueness is not
> > > checked at all, the query is reduced by all columns that don't belong
> > > to any of the unique constraints (or that don't belong to the chosen
> > > unique constraint), then it is run and the first row is returned?
> >
> > It would mean that DBIC would accept the user saying "I know you can't tell
> > but this is unique". Possibly we should also check to see if the sth is
> > exhausted after getting the single row and produce a warning or exception
> > if not.
> 
> Great!  That is what I believe is needed.

I believe a warning in Storage::DBI's single() method would do the trick.

> > >
> > > When you do know the PK then you would call find, when you do know
> > > that you have no PK then you would directly call create or new.  It is
> > > only when you don't know that you need any of these listed methods.
> >
> > I think you're (a) assuming PK rather than one of N unique keys, (b)
> > assuming an auto-increment or other surrogate PK rather than a natural one.
> >
> > Much of the utility of the *_or_* methods is when one or both of these is
> > not the case.
> 
> It's hard to analyse that without use cases.  Here is the one that I
> was mostly thinking about:
> 
> Code to edit/create a record from web form parameters.  You receive a
> bunch of columns and you need to update the record identified by the
> columns that form the PK or create a new one if there is no such
> column (including the case when the PK parameters are set to 'undef'
> so that they would receive the default value from the DB).   It would
> be very useful to have a method on the resultset that would
> automatically analyse the parameters and do the right thing.
> update_or_create is unfortunately unsuitable for that - because you
> cannot delete the PK from the list of parameters even if it is undef
> (otherwise find will not always work as expected) and you cannot leave
> it there if it is undef - beause then create will fail.

Ok, but as I've already noted the fact that deleting it buggers up find()
is a bug (personally I think not knowing whether the operation is a create
or an update is also almost always a bug, but that's a matter of taste)

$rs->update_or_create(\%params, { key => 'primary' })

-should- be safe in this case, provided you don't pass undef for the PK
which means "try and INSERT NULL" not "receive the default value" - as Carl
noted that's a bug in FormFu and DBIC behaves correctly in the { id => undef }
case.

Note, by 'should' I do mean should, not 'is'. But I already started a
thread to discuss the behaviour of find etc. and how to fix it so please
post about that there, not here - the ones you started had got hopelessly
confused because your writing style tends to be wordy and vague (several
people have commented they were lost which is why I started the fresh thread)
and bullet points and concision work rather better to summarise technical
issues ;)
 
> And just to explain myself - I really try to contribute to the project
> - and I hope that this documenting of the gotchas that an
> unexperienced DBIC programmer can encounter when using it is a
> contribution and not an evil attack.

Certainly, if you document clearly and accurately. The post of yours that
started this thread was neither and as an added bonus quoted me to support
a point that wasn't actually what the quote was referring to.

What that post left to itself would have achieved instead is to scare the
shit out of potential new users with things that (a) aren't entirely
accurate (b) are easily interpreted four different ways (c) will hopefully
be fixed or at least much improved in a month or two.

That wasn't constructive at all. Next time please try going for "this is
my understanding of the situation, could people please confirm or correct"
- just like I do when I'm asking about stuff.

-- 
      Matt S Trout       Need help with your Catalyst or DBIx::Class project?
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