Question

class Child < ApplicationRecord
  belongs_to :parent
end

class Parent < ApplicationRecord
  has_many :children
end

irb(main):073:0> child = Child.last
  Child Load (0.4ms)  SELECT  "children".* FROM "children" ORDER BY "children"."id" DESC LIMIT $1  [["LIMIT", 1]]
+----+----------------------+-----------+---------------------------+---------------------------+
| id | title                | parent_id | created_at                | updated_at                |
+----+----------------------+-----------+---------------------------+---------------------------+
| 1  | this is childs title | 1         | 2018-08-23 12:09:37 +0900 | 2018-08-23 12:09:37 +0900 |
+----+----------------------+-----------+---------------------------+---------------------------+
1 row in set
irb(main):074:0> child.save
   (0.4ms)  BEGIN
  Parent Load (0.5ms)  SELECT  "parents".* FROM "parents" WHERE "parents"."id" = $1 LIMIT $2  [["id", 1], ["LIMIT", 1]]
   (0.4ms)  COMMIT
=> true

代码是这样的。当我保存孩子时，将发生父选择查询。我不知道为什么会发生这种情况，有可能避免这种情况吗？

在我的情况下，父级有许多列且很大，因此自动加载它会占用大量内存。

Answer 1

通过这种方式，您可以避免在保存孩子之前先致电给父母

Child.new(title: 'this is childs title', parent_id: parent.id)

Ruby on Rails active_record：保存子级时，将发生父级选择查询。为什么以及如何避免这种情况？

1 个答案: