從左加入主動記錄的字段總和

Question

如何獲得capacity.capacity的總和？

@capacitysum = User.joins("left join capacities c on users.id = c.user_id") 
.where('c.created_at = (SELECT MAX(c.created_at) FROM c WHERE c.user_id = users.id)') 
.where('users.role = ?', 'consultant') 

我嘗試添加一個的.sum（ 'c.capacity'）的.sum（：容量）和的.sum（ 'capacities.capacity'），但沒有成功...

Answer 1

嘗試用加select語句：

@capacitysum = User.joins("left join capacities c on users.id = c.user_id") 
.where('c.created_at = (SELECT MAX(c.created_at) FROM c WHERE c.user_id = users.id)') 
.where('users.role = ?', 'consultant').select("sum(c.capacity)")