Rails 从连接表中删除记录：使用附加连接时，delete_all 失败

Question

我的模特：

class User < ApplicationRecord
  has_and_belongs_to_many :comments
end

class Comment < ApplicationRecord
  belongs_to :book

  has_and_belongs_to_many :users
end

class CommentsUser < ApplicationRecord
  belongs_to :comment
  belongs_to :user
end

我可以通过连接进行常规选择：

users_ids = [197]
book_id   = 659

CommentsUser.joins(:comment).where(comments: {book_id: book_id}, user_id: users_ids)
# CommentsUser Load (0.5ms)  SELECT "comments_users".* FROM "comments_users" INNER JOIN "comments" ON "comments"."id" = "comments_users"."comment_id" WHERE "comments"."book_id" = $1 AND "comments_users"."user_id" = $2  [["book_id", 659], ["user_id", 197]]

但是如果我使用delete_all，它会失败（注意

"comments_users".""

：

CommentsUser.joins(:comment).where(comments: {book_id: book_id}, user_id: users_ids).delete_all
# CommentsUser Destroy (0.8ms)  DELETE FROM "comments_users" WHERE ("comments_users"."") IN (SELECT "comments_users"."" FROM "comments_users" INNER JOIN "comments" ON "comments"."id" = "comments_users"."comment_id" WHERE "comments"."book_id" = $1 AND "comments_users"."user_id" = $2)  [["book_id", 659], ["user_id", 197]]

# ActiveRecord::StatementInvalid: PG::SyntaxError: ERROR:  zero-length delimited identifier at or near """"
# LINE 1: ...comments_users" WHERE ("comments_users"."") IN (SE...

我想使用第一个语句中使用的相同逻辑来删除记录 - 我可以找到记录，但无法删除它们 - 有什么想法吗？

Answer 1

在 HABTM（Has and Belongs to Many）关系中，Rails 默认情况下不会为连接表生成主键。使用联接时，Rails 会尝试引用表的主键，而缺少主键可能会在尝试删除记录时导致 SQL 语法错误。

您可以先选择记录的ID，然后进行删除操作：

CommentsUser.where(
  id: CommentsUser.joins(:comment)
                   .where(comments: { book_id: book_id }, user_id: users_ids)
                   .select(:id) ).delete_all

或者，您可以使用

has_many :through

关联代替

has_and_belongs_to_many

，它允许连接表具有主键。