[Catalyst] Chained actions usage and DBIC performance

[John Napiorkowski]

--- Nilson Santos Figueiredo Junior <acid06 at gmail.com>
wrote:

> Lately I've been using chained actions a lot, since
> it ends up making
> everything look cleaner and more organized.
> 
> I tend to structure things in a way that I've got
> some Catalyst
> actions that load some items from the database  
> which are the root of
> the chain and then I've got another set of Catalyst
> actions that
> actually do things with those loaded items (e.g.
> /item/12/view,
> /item/12/edit, and so on).
> 
> Sometimes, those items also have subitems and those
> might even have
> another set of subitems. In these cases, when using
> Catalyst and
> DBIx::Class it can be useful to prefetch stuff for
> performance
> reasons. But, using my setup it's not currently
> possible to do that,
> so I end up issuing lots of queries to the database
> since the initial
> root item didn't prefetch anything, because it
> couldn't know in
> advance what would be needed by the chained actions.
> 
> Most of the item loading code I've previously
> mentioned looks like
> this (simplified):
> 
>   sub load : Chained('/item') PathPart('')
> CaptureArgs(1) {
>     my ($self, $c, $id) = @_;
>     $c->stash->{item} = $c->model('DB')->find($id);
>   }
> 
> The only work around I could think of is to prefetch
> everything and
> hope that it would result in a performance gain, at
> least on average.
> But, honestly, I find it a kind of crappy solution
> so I didn't even
> implement it.
> 
> I'd like to know how people usually handle this
> because there must a
> better way than ignoring performance concerns at
> all.
> 
> The only better way I could think of would be if
> DBIC's ->find()
> worked in a similar way to ->search() and only
> actually fetched the
> values when they were needed. So I could add
> prefetch conditions
> arbitrarily using stacked find() calls. Maybe this
> should be suggested
> on DBIC mailing list? Or am I just complicating a
> trivial situation
> and there's a simple way around this problem?
> 
> -Nilson Santos F. Jr.
> 
I do something very similar to what you are talking
about but I don't issue a find until the endpoint. 
You can do search anywhere you do find to get
resultsets.  That why you can drill down and keep
adding conditions to the query down the chain.  I find
this works pretty well, I only ever see a single
dtabase call.

--john

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