`@ post.userview.users << current_user`

Question

每个帖子都有一个用户视图，每个用户视图都有很多用户。我想要一个单一的多对多有一个简单的.add()和.remove()函数像django。如何将current_user置于视图的多对多关系中？

我找到了这个：

@post.userview.users << current_user

但它会带来一些SQL错误。它建议我添加一个post_id：

ERROR:  column userviews.post_id does not exist
LINE 1: SELECT  "userviews".* FROM "userviews" WHERE "userviews"."po...
                                                     ^
HINT:  Perhaps you meant to reference the column "userviews.posts_id".

答案之后，现在的错误是：

can't write unknown attribute `userview_id`

因为我稍微改变了迁移，所以userview引用了帖子和用户。发布has_one userview，has_many用户通过userview，userview has_many发布和has_many用户。

create_table "posts", force: :cascade do |t|
    t.integer "userview_id"
    t.bigint "userviews_id"
    t.index ["userviews_id"], name: "index_posts_on_userviews_id"
  end

create_table "userviews", force: :cascade do |t|
    t.bigint "users_id"
    t.bigint "posts_id"
    t.integer "post_id"
    t.integer "user_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["posts_id"], name: "index_userviews_on_posts_id"
    t.index ["users_id"], name: "index_userviews_on_users_id"
  end





class User < ActiveRecord::Base
  has_many :viewed_posts, through: :userview, class_name: 'Post'
...


class Userview < ApplicationRecord
    belongs_to :post
    belongs_to :user
end


class Post < ApplicationRecord
    belongs_to :user
    has_many :userviews
    has_many :viewers, through: :userview, class_name: 'User'
...


Could not find the source association(s) "viewer" or :viewers in model Userview. Try 'has_many :viewers, :through => :userviews, :source => <name>'. Is it one of post or user?

虽然，这是为unless @post.viewers.include?(current_user)

Answer 1

不确定我是否正确理解你想要实现的目标，但我会尝试修复你的联想。

要关联2个模型，您需要将外键存储在其中一个模型中。存储关键belongs_to其他模型的模型。例如在posts表中你有user_id列，它意味着post belongs_to: user和用户has_many :posts（如果你需要一对一的关联，则为has_one :post）。对于这种关联，您可以写：

user = User.first
post = Post.last
user.posts << post

如果您希望所有这些东西自动运行，您应该遵循有关命名的约定。外键应该是单数形式，如user_id，而不是users_id

如果需要多对多关联，则需要创建一个存储两个外键的中间表。它可以使用简单的直接has_and_belongs_to_many关联或更复杂的has_many through:来完成

我认为在你的情况下它应该是：

class User < ActiveRecord::Base
  has_many :userviews
  # it is posts viewed by the user
  # you need to specify class name because it differs from association name
  has_many :viewed_posts, through: :userviews, class_name: 'Post' 

  # posts written by the user
  has_many :posts 
end

class Userview < ApplicationRecord
  belongs_to :post
  belongs_to :user
end

class Post < ApplicationRecord
  belongs_to :user
  has_many :userviews
  has_many :viewers, through: :userviews, source: :user
end

这意味着你需要post_id表中的user_id和userviews列以及user_id表中的posts。请删除无用的列并在迁移中添加所需的列。当你正确地设置它时，你将能够做到

@post.viewers << current_user

将current_user添加到查看者列表。相应的用户视图实例自动创建

Answer 2

改变了has_many :viewers, through: :userviews, class_name: 'User'

到has_many :viewers, through: :userviews, source: :user