[Dbix-class] Re: DBIx::Class::ResultSet::RecursiveUpdate - announcement and RFC

[Matt S Trout]

On Wed, Oct 01, 2008 at 09:38:07AM +0200, Zbigniew Lukasiak wrote:
> On Wed, Oct 1, 2008 at 3:17 AM, Matt S Trout <dbix-class at trout.me.uk> wrote:
> > On Tue, Sep 30, 2008 at 02:39:00PM +0200, Zbigniew Lukasiak wrote:
> >> On Tue, Sep 30, 2008 at 2:20 PM, Matt S Trout <dbix-class at trout.me.uk> wrote:
> >> > On Tue, Sep 30, 2008 at 09:28:50AM +0200, Zbigniew Lukasiak wrote:
> >> >> The tricky part is when you load data from the form into the new row.
> >> >> You need to delete the pk from it - because otherwise at
> >> >> update_or_insert time it would issue an insert with pk = NULL - and
> >> >> this will fail in Pg (for example).  The point is that you cannot feed
> >> >> the same data to the find and to the insert calls - but
> >> >> update_or_create does that - and why it does not have much choice is
> >> >> another very long story.
> >> >
> >> > Well, yes. If you have an auto-increment PK and you don't have a value for
> >> > it, then
> >> >
> >> > (1) there's no form field in the first place, so that's not an issue
> >> >
> >> > (2) you know you can't possibly find anything, so you wouldn't call
> >> > update_or_create, you'd just call create
> >> >
> >> > I presume this is what Oliver's doing, which is why his code works.
> >> >
> >> > Nothing tricky at all.
> >>
> >> This method assumes that you don't get the PK in the ResultSet in the
> >> internal conditions.  I is ok if you have the full controll over the
> >> ResultSet - but if you do admit this possibility (for example when you
> >> traverse a belongs_to relation, or if you use RestrictedWithObject) -
> >> then you would have to inspect it o check what part of the PK is there
> >> to decide if you should  go directly to ->create.  Since currently
> >> there is no easy and sound way of doing this inspection (and for some,
> >> rather convoluted - I admit, cases it is impossible - that is it is
> >> undecidable - i.e. cannot be solved by an algorithm) - this makes this
> >> method unsuitable for my purposes.
> >
> > I don't see that this would ever happen with an auto-inc PK though.
> >
> > And if it's a unique key, the behaviour is rather different.
> >
> > Basically, I've not yet seen a real world example where this situation
> > actually comes up, and I can't think of a contrived one that doesn't come
> > into the category of "your design is broken".
> >
> > So it's so far a problem in theory but not in practice - can you provide
> > a real example of this situation?
> 
> The example that I am mostly concerned with is:
> 
> $cd_rs->recursive_update( { title => 'New Title', artist => { name =>
> 'New Name' } } )
> 
> Now when traversing the relation from cd to the artist I get the
> artist resultset with the PK constrained in the ->{cond}.  There is
> just one artist that the cd 'belongs_to' - and that artist should be
> updated.  But there is no PK passed in the parameters - so if we just
> look at the parameters we would  conclude that this would require a
> ->create call.

Ah, because the artist is about to be changed?

In that case you should create the artist separately and then assign it
I think, which again avoids the problem.

Better ideas welcome.

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