perl – DBIx :: Class示例

my $rs = $schema->resultset('CD')->search(
{
  'artist.name' => 'Bob Marley'
  'liner_notes.notes' => { 'like','%some text%' },},{
  join     => [qw/ artist liner_notes /],order_by => [qw/ artist.name /],}
);

DBIx cookbook说这是将生成的sql：

# Equivalent SQL:
# SELECT cd.*,artist.*,liner_notes.* FROM cd
# JOIN artist ON cd.artist = artist.id
# JOIN liner_notes ON cd.id = liner_notes.cd
# WHERE artist.name = 'Bob Marley'
# ORDER BY artist.name

但是从菜谱的其余部分开始,我一直认为查询只会选择cd.*,除非当然使用prefetch是这样的：

my $rs = $schema->resultset('CD')->search(
{
  'artist.name' => 'Bob Marley'
  'liner_notes.notes' => { 'like',prefetch => [qw/ artist liner_notes/],}
);

以下是让我相信这一点的陈述：

[Prefetch] allows you to fetch results from related tables in advance

任何人都可以向我解释我在这里缺少的东西吗？或不？非常感谢！