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POPerl: DBIx::Class Beginner - Subsetting Relationships and Prefetching
 

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  1. POPerl: DBIx::Class Beginner - Subsetting Relationships and Prefetching
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    <p>Okay, I'm new to DBIx::Class. I have a one-to-many relationship set up, like so:</p> <pre><code>User -&gt; has_many -&gt; Addresses </code></pre> <p>Okay, good. I can do a query, and call it prefetching JOINed tables, like so:</p> <pre><code>Foo::DBIC-&gt;storage-&gt;debug(1); # output SQL to STDOUT my $user = Foo::DBIC-&gt;resultset('Users')-&gt;search({}, { prefetch =&gt; [ 'addresses' ], join =&gt; [ 'addresses' ], rows =&gt; 1 })-&gt;single; for my $address ($user-&gt;addresses-&gt;all) { say $address-&gt;zip_code; } </code></pre> <p>Two tables, one SQL query (verified via debug). All is well.</p> <p>Now, however, let's say I want to write an overload method or two in Foo::DBIC::Result::Users that returns a <em>subset</em> of addresses, based on certain criteria. Here's what I've added to the Users class:</p> <pre><code>sub home_addresses { my $self = shift; return $self-&gt;search_related('addresses', { address_type =&gt; 'home' }); } sub business_addresses { my $self = shift; return $self-&gt;search_related('addresses', { address_type =&gt; 'business' }); } </code></pre> <p>I can call these overloads like so, and they work:</p> <pre><code>for my $address ($user-&gt;home_addresses-&gt;all) { say $address-&gt;zip_code; } </code></pre> <p>However, this <em>ignores</em> the fact that I've prefetched my join, and it performs ADDITIONAL QUERIES (as if I've not prefetched and joined anything).</p> <p>So, my question is this: how do I define an overload method that returns a subset of a related table, but uses the already prefetched join? (just appending a WHERE clause to the prefetch)...</p> <p>My problem is that if I have a lot of the overloaded methods returning related table subsets, my query count can blow up; especially if I'm calling them from within a loop.</p> <p>I have reasons for doing this that are, of course, ugly. My real life schema is a lot, lot, lot messier than Users and Addresses, and I'm trying to abstract away ugly as best I can.</p> <p>Thanks!</p>
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    1. USJoshua Pruitt
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      1. VTUpMod
    1. COSince you don't want to re-query the database, why are you calling DBIC methods? You will gain no advantage query wise, just write methods that filter the returned data with perl functions (like grep).
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    2. COI wonder why you call them overloaded methods? Overloading in Perl is when you for example define what an object should return in numerical context.
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      1. USAlexander Hartmaier
    3. COBecause I suck at words. I was thinking in terms of "overloading a column accessor", but actually I'm just creating a new accessor method anyway. Whatever, you knew what I meant.
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      1. USJoshua Pruitt
 

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