Rails Active 查询按特定顺序按多个值排序? [英] Rails Active query order by multiple values in specific order?

问题描述

我有一张桌子

Roles(id int,,name vachar(50),role enum(CAD,CA,CM,CV ))

我想选择按特定顺序按特定值排序的数据.我的活动模型查询:role.order('role asc') 然后结果:

I want select data that order by specific values in specific order . My active model query: role.order('role asc') then the result:

1 name1 CAD
2 name2 CA
3 name2 CM

但我想要这样的结果:

1 name1 CAD
2 name2 CM
3 name2 CA

谁能帮帮我?提前致谢

推荐答案

一个可移植的解决方案是将 CASE 语句用作 ORDER BY 中的内联映射:

A portable solution would be to use a CASE statement as an inlined map in your ORDER BY:

query.order(%q(
  case role
  when 'CAD' then 1
  when 'CM'  then 2
  when 'CA'  then 3
  end
))

请记住，您可以按您想要的任何表达式进行 ORDER BY，并且 CASE 当然是 SQL 中的一个表达式.

Keep in mind that you can ORDER BY any expression you want and a CASE certainly is an expression in SQL.

较新版本的 Rails 会希望您使用 Arel.sql 而不是原始字符串:

Newer versions of Rails will want you to use Arel.sql rather than a raw string:

query.order(
  Arel.sql(
    %q(
      case role
      when 'CAD' then 1
      when 'CM'  then 2
      when 'CA'  then 3
      end
    )
  )
)

如果列表是动态的，您可以构建一个 CASE 表达式:

And if the list is dynamic, you can build a CASE expression:

array = %w[CAD CM CA]
q     = connection.method(:quote) # Or ApplicationRecord.connection.method(:quote)
cases = array.each_with_index.map { |e, i| "when #{q[e]} then #{i}" }
query.order(Arel.sql("case role #{cases.join(' ')} end"))

所有的字符串操作都有点难看，但它是完全安全的，您通常会将其隐藏在作用域中.

All the string manipulation is a bit ugly but it is perfectly safe and you'd usually hide it in a scope.

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