[Dbix-class] BUG? Unable to resolve relationship

Peter Rabbitson rabbit+dbic at rabbit.us
Sat Dec 12 10:01:46 GMT 2009

Ovid wrote:
> This is for DBIx::Class version 0.08115, but it happens with 08114.  This is the smallest test case I could get:
>     #!/usr/bin/env perl
>     use strict;
>     use warnings;
>     my $db = 'test.db';
>     my $sql = <<'END';
>     create table customer (
>         id    int primary key, 
>         name  varchar(10) not null, 
>         account_id int null,
>         foreign key(account_id) references account(id)
>     );
>     create table account  (
>         id int primary key,
>         type varchar(10)
>     );
>     insert into account values ( 1, 'Premium');
>     END
>     unlink $db if -f $db;
>     open my $fh, "| sqlite3 $db" or die "Cannot pipe to sqlite3: $!";
>     print $fh $sql or die $!;
>     close $fh or die $!;
>     {
>         package The::Schema;
>         use base qw/DBIx::Class::Schema::Loader/;
>     }
>     my $schema = The::Schema->connect("dbi:SQLite:dbname=$db");
>     The::Schema::Customer->might_have( "account", "The::Schema::Account",
>         { "foreign.id" => "self.account_id" } );
>     my $cust = $schema->resultset('Customer')->create( { name => 'john' } );
>     print $cust->account->type;
> In DBIx::Class::VERSION 0.08010 (our current version at work), if you run this code and print $cust->account->type, and it prints "Premium", even though we have deliberately excluded an account.

This was a bug.

> When I upgrade to 0.08115:
>   My::Schema::Customer::account(): Unable to resolve relationship from Customer to account: column account.account_id not loaded from storage (or not passed to new() prior to insert()). Maybe you forgot to call ->discard_changes to get defaults from the db. at loader.pl line 7

This is correct and expected. Read the error message more carefully. To break it down:

*) You create a row, without specifying a value for account_id.
*) The resulting object has only a name, and its autoinc id, dbic does not assume
that the value of account_id is NULL/undef, it simply isn't there (i.e. the db-side
default may be 0, or 42 or 'kinky sex')
*) Since there is no value for the FK, the relationship can not be resolved and
subsequently the exception you see is thrown.
*) If you do what has been suggeste d- call discard_changes to make a db-trip to
retrieve the missing values - everything will just work. Alternatively you can
create() the row explici5tly specifying account_id => undef - this will work as
expected too.

Alo the relationship naming is a bot unfortunate, the documentation indeed needs
some improvement. Should be available in the next release.

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