Rails的2.3：如何把这个SQL语句转换成一个named_scope [英] Rails 2.3: How to turn this SQL statement into a named_scope

问题描述

有一点困难，搞清楚如何从这个SQL查询创建named_scope：

SELECT *从foo其中ID NOT IN（选择foo_id从巴），foo.category =？ ORDER BY RAND（）LIMIT 1;

范畴应变量发生变化。

什么是named_scope可以为问题待写入的最有效的方式以上？

解决方案

  named_scope：SCOPE_NAME，拉姆达{|类别|
    {
      ：条件=＆GT; [ID NOT IN（选择foo_id从巴），foo.category =？，类别】，
      ：为了=＆GT; RAND（），
      ：上限=＆GT; 1
    }
  }
 

Having a bit of difficulty figuring out how to create a named_scope from this SQL query:

select * from foo where id NOT IN (select foo_id from bar) AND foo.category = ? ORDER BY RAND() LIMIT 1;

Category should be variable to change.

What's the most efficient way the named_scope can be written for the problem above?

解决方案

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

这篇关于Rails的2.3：如何把这个SQL语句转换成一个named_scope的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！