由
生成的记录数组+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| id | name | head | apr | may | jun | jul | aug | sep | oct | nov | dec | jan | feb | mar | total |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 1 | A | basic | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 1000 | 12000 |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 1 | A | hra | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 6000 |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 2 | B | basic | 2000 | 2000 | 2000 | 2000 | 2000 | 2000 | 2000 | 2000 | 2000 | 0 | 0 | 2000 | 24000 |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 2 | B | hra | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 0 | 0 | 500 | 6000 |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 3 | C | basic | 5000 | 5000 | 5000 | 5000 | 5000 | 5000 | 0 | 0 | 0 | 5000 | 5000 | 5000 | 60000 |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 3 | C | hra | 500 | 500 | 500 | 500 | 500 | 500 | 0 | 0 | 0 | 500 | 500 | 500 | 6000 |
+----+------+-------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
将包含一个或多个签名的操作。
@signatures = Signature.where('action_id IN (?)', @actions).all
什么ruby指令可以根据action_id提取单个案例？上例中的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
答案 0 :(得分：2)
@signatures = Signature.where(action_id: @actions)
.group('action_id')
.select('id, count(action_id)')
.having('count(action_id) = 1')