ruby-on-rails - 从数组中提取单个案例

Question

由

生成的记录数组

@signatures = Signature.where('action_id IN (?)', @actions).all

将有一个或多个签名的 Action 。

Signature id: 1, action_id: 1
Signature id: 2, action_id: 2
Signature id: 3, action_id: 1
Signature id: 4, action_id: 3
Signature id: 5, action_id: 2

什么 ruby​​ 指令可以根据 action_id 提取单个案例？上例中的Signature.id = 4

Answer 1

@signatures = Signature.where(action_id: @actions)
                       .group('action_id')
                       .select('id, count(action_id)')
                       .having('count(action_id) = 1')