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

[Matt S Trout]

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?

-- 
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