ruby-on-rails - has_and_belongs_to_many 给出 "no such table"错误

Question

我在文件和联系人之间有一个多对多的关系，因此他们有 has_and_belongs_to_many 关系:

class Dossier < ActiveRecord::Base
  has_and_belongs_to_many :contacts

和

class Contact < ActiveRecord::Base
  has_and_belongs_to_many :dossiers

在 Dossiers Controller 显示方法中，我有这个:

@dossier = current_user.company.dossiers.find(params[:id])    
@dossier_contacts = @dossier.contacts

但是当我请求显示 View 时，出现错误:

SQLite3::SQLException: no such table: contacts_dossiers: SELECT COUNT(*) FROM "contacts" INNER JOIN "contacts_dossiers" ON "contacts"."id" = "contacts_dossiers"."contact_id" WHERE "contacts_dossiers"."dossier_id" = 1

View 如下所示:

<li><%= I18n.t :dossier_nr_contacts %></li><li><%= @dossier_contacts.count.to_s %></li>

我想我已经设置了正确的关系，表格存在，但我现在不知道为什么它会给出错误。有什么线索吗？

编辑:我所做的迁移:

class CreateDossiersContactsJoinTable < ActiveRecord::Migration
  def up
    create_table :dossiers_contacts, :id => false do |t|
      t.integer :dossier_id
      t.integer :contact_id
    end
  end

  def self.down
    drop_table :dossiers_contacts
  end
end

Answer 1

您的连接表名称错误。

应该是 contacts_dossiers (默认按字母顺序)

If you create a has_and_belongs_to_many association, you need to explicitly create the joining table. Unless the name of the join table is explicitly specified by using the :join_table option, Active Record creates the name by using the lexical order of the class names. So a join between customer and order models will give the default join table name of “customers_orders” because “c” outranks “o” in lexical ordering.

来源: http://guides.rubyonrails.org/association_basics.html#creating-join-tables-for-has_and_belongs_to_many-associations