如何按特定prority对activerecord查询进行排序

Question

我正在使用rails 3和postrges.

我希望按特定优先顺序排序.

就像是:

Assignment.order(priority: ['best', 'good', 'bad'])

这将首先以"最佳",然后"好",然后"坏"返回所有活动记录

我似乎无法找到这样的东西.我不需要数组,它必须是activerecords.

Answer 1

订单可以是任何SQL代码.您可以使用CASE语句将值映射到自然按正确顺序排序的值.

Assignment.order("
    CASE
      WHEN priority = 'best' THEN '1'
      WHEN priority = 'good' THEN '2'
      WHEN priority = 'bad' THEN '3'
    END")

更好的是,您可以将此逻辑移动到模型中,以便从控制器调用更容易:

class Assignment < ActiveRecord::Base
  ...
  def self.priority_order
    order("
        CASE
          WHEN priority = 'best' THEN '1'
          WHEN priority = 'good' THEN '2'
          WHEN priority = 'bad' THEN '3'
        END")
  end
end

然后你可以打电话Assignment.priority_order来获取你的排序记录.

如果此列在视图中可排序,请向方向添加参数:

def self.priority_order(direction = "ASC")
  # Prevent injection by making sure the direction is either ASC or DESC
  direction = "ASC" unless direction.upcase.match(/\ADESC\Z/)
  order("
      CASE
        WHEN priority = 'best' THEN '1'
        WHEN priority = 'good' THEN '2'
        WHEN priority = 'bad' THEN '3'
      END #{direction}")
end

然后,您将调用Assignment.priority_order(params[:direction])从控制器传递排序.

Answer 2

在较新版本的 Rails 中，ActiveRecord::UnknownAttributeReference (Query method called with non-attribute argument(s)如果将原始 SQL 传递给.order().

您需要用 包装您的 SQL 查询Arel.sql()。您还可以使用 ruby​​ 的Here Doucment语法来编写多行 SQL 语句，并压缩以使其在控制台中更具可读性。

所以整个事情就变成了：

Assignment.order(
  Arel.sql(<<-SQL.squish
    CASE
      WHEN priority = 'best' THEN '1'
      WHEN priority = 'good' THEN '2'
      WHEN priority = 'bad' THEN '3'
    END
  SQL
  )
)