ruby-on-rails - rails 2.3 : How to turn this SQL statement into a named_scope

Question

弄清楚如何从这个 SQL 查询创建一个 named_scope 有点困难:

select * from foo where id NOT IN (select foo_id from bar) AND foo.category = ?按 RAND() 限制 1 排序；

类别应该是可变的。

针对上述问题编写命名范围的最有效方式是什么？

Answer 1

  named_scope :scope_name, lambda { |category|
    { 
      :conditions => ["id NOT IN (select foo_id from bar) AND foo.category = ?", category],
      :order => 'RAND()',
      :limit => 1
    }
  }