没有看到您的控制器或表单，很难确定具体是什么导致了您的问题。除了上面@surya 的评论之外，我注意到belongs_to您班级中的两个语句UsersContact应该是单数，而不是复数（:user, :contact）。另外，不确定您是否需要嵌套users_contacts_attributes在contacts_attributes其中然后使它嵌套两个深度，以便user您可以accepts_nested_attributes_for :users_contacts在User类中单独使用。
除此之外，您必须将您的代码与我在下面提供的代码进行比较，看看您是否能找到问题所在。
注意：表格非常基本，我修改了一些名称，以便更清楚地表明何时使用单数和复数以及为了便于阅读。
楷模
class User < ActiveRecord::Base
has_many :user_contact_pairs, inverse_of: :user
has_many :contacts, through: :user_contact_pairs
accepts_nested_attributes_for :contacts, allow_destroy: true
accepts_nested_attributes_for :user_contact_pairs, allow_destroy: true
end
class Contact < ActiveRecord::Base
has_many :user_contact_pairs, inverse_of: :contact
has_many :users, through: :user_contact_pairs
accepts_nested_attributes_for :user_contact_pairs, allow_destroy: true
end
class UserContactPair < ActiveRecord::Base
belongs_to :contact
belongs_to :user
end
控制器
class UsersController < ApplicationController
before_action :set_user, only: [:show, :edit, :update, :destroy]
def index
@users = User.all
end
def show
end
def new
@user = User.new
end
def edit
@user.user_contact_pairs.build(user_id: @user.id)
end
def create
@user = User.new(user_params)
respond_to do |format|
if @user.save
format.html { redirect_to @user, notice: 'User was successfully created.' }
format.json { render :show, status: :created, location: @user }
else
format.html { render :new }
format.json { render json: @user.errors, status: :unprocessable_entity }
end
end
end
def update
respond_to do |format|
if @user.update(user_params)
format.html { redirect_to @user, notice: 'User was successfully updated.' }
format.json { render :show, status: :ok, location: @user }
else
format.html { render :edit }
format.json { render json: @user.errors, status: :unprocessable_entity }
end
end
end
def destroy
@user.destroy
respond_to do |format|
format.html { redirect_to users_url, notice: 'User was successfully destroyed.' }
format.json { head :no_content }
end
end
private
def set_user
@user = User.find(params[:id])
end
def user_params
params.require(:user).
permit(:email, :first_name, :last_name, :username,
contacts_attributes:
[:id, :first_name, :last_name],
user_contact_pairs_attributes:
[:id, :contact_id, :user_id, :order_number])
end
end
查看（用户/index.html.erb）
<p id="notice"><%= notice %></p>
<h1>Listing Users</h1>
<table>
<thead>
<tr>
<th colspan="3"></th>
</tr>
</thead>
<tbody>
<tr>
<td><%= 'Id' %></td>
<td><%= 'First Name' %></td>
<td><%= 'Last Name' %></td>
<td><%= 'Username' %></td>
<td></td>
<td></td>
<td></td>
</tr>
<% @users.each do |user| %>
<tr>
<td><%= user.id %></td>
<td><%= user.first_name %></td>
<td><%= user.last_name %></td>
<td><%= user.username %></td>
<td><%= link_to 'Show', user %></td>
<td><%= link_to 'Edit', edit_user_path(user) %></td>
<td><%= link_to 'Destroy', user, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
</tbody>
</table>
<br>
<%= link_to 'New User', new_user_path %>
查看（用户/edit.html.erb）
<h1>Editing User</h1>
<%= render 'form' %>
<%= link_to 'Show', @user %> |
<%= link_to 'Back', users_path %>
查看（用户/_form.html.erb）
<%= form_for(@user) do |user_form| %>
<% if @user.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@user.errors.count, "error") %> prohibited this user from being saved:</h2>
<ul>
<% @user.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= user_form.label :email %>
<%= user_form.email_field :email %><br>
<%= user_form.label :first_name %>
<%= user_form.text_field :first_name %><br>
<%= user_form.label :last_name %>
<%= user_form.text_field :last_name %><br>
<%= user_form.label :username %>
<%= user_form.text_field :username %><br>
</div>
<h2>User Contact Pair</h2>
<%= user_form.fields_for :user_contact_pairs do |ucp_fields| %>
<div class="user-contact-pair">
<div class="field">
<%= ucp_fields.label :contact_id %>
<%= ucp_fields.number_field :contact_id %><br>
<%= ucp_fields.label :order_number %>
<%= ucp_fields.number_field :order_number %><br>
</div>
</div>
<% end %>
<div class="actions">
<%= user_form.submit %>
</div>
<% end %>
迁移
class CreateUser < ActiveRecord::Migration
def change
create_table :users do |t|
t.string :email, index: { unique: true }
t.string :first_name
t.string :last_name
t.string :username, index: { unique: true }
t.timestamps null: false
end
end
end
class CreateContact < ActiveRecord::Migration
def change
create_table :contacts do |t|
t.string :first_name
t.string :last_name
t.timestamps null: false
end
end
end
class CreateUserContactPair < ActiveRecord::Migration
def change
create_table :user_contact_pairs do |t|
t.integer :contact_id
t.integer :user_id
t.integer :order_number
t.timestamps null: false
end
end
end
数据库种子文件
User.create(email: 'lhawkinsa@icio.us', first_name: 'Lisa', last_name: 'Hawkins', username: 'lhawkinsa')
User.create(email: 'htaylorb@imdb.com', first_name: 'Helen', last_name: 'Taylor', username: 'htaylorb')
User.create(email: 'gtaylorc@unblog.fr', first_name: 'Gregory', last_name: 'Taylor', username: 'gtaylorc')
User.create(email: 'hlaned@whitehouse.gov', first_name: 'Henry', last_name: 'Lane', username: 'hlaned')
User.create(email: 'hphillipse@howstuffworks.com', first_name: 'Harry', last_name: 'Phillips', username: 'hphillipse')
User.create(email: 'jgonzalesf@com.com', first_name: 'Jeffrey', last_name: 'Gonzales', username: 'jgonzalesf')
User.create(email: 'ljamesg@sfgate.com', first_name: 'Lori', last_name: 'James', username: 'ljamesg')
User.create(email: 'rhillh@gnu.org', first_name: 'Roger', last_name: 'Hill', username: 'rhillh')
User.create(email: 'rharveyi@tripadvisor.com', first_name: 'Raymond', last_name: 'Harvey', username: 'rharveyi')
User.create(email: 'sperryj@mit.edu', first_name: 'Stephen', last_name: 'Perry', username: 'sperryj')
Contact.create(first_name: 'Louis', last_name: 'Harris')
Contact.create(first_name: 'Fred', last_name: 'Adams')
Contact.create(first_name: 'David', last_name: 'Lane')
Contact.create(first_name: 'Kevin', last_name: 'Ryan')
Contact.create(first_name: 'Samuel', last_name: 'Jones')
Rails 控制台（通过表单进行两次用户更新后）
Running via Spring preloader in process 30656
Loading development environment (Rails 4.2.7.1)
2.3.3 :001 > UserContactPair.all
UserContactPair Load (0.7ms) SELECT "user_contact_pairs".* FROM "user_contact_pairs"
=> #<ActiveRecord::Relation [#<UserContactPair id: 1, contact_id: 1, user_id: 1, order_number: 1, created_at: "2017-02-14 09:05:31", updated_at: "2017-02-14 09:05:31">, #<UserContactPair id: 2, contact_id: 4, user_id: 1, order_number: 4, created_at: "2017-02-14 09:05:50", updated_at: "2017-02-14 09:05:50">]>
2.3.3 :002 >
更新（回应评论）：
这是更新的代码，应该可以满足您的要求。您应该考虑在上述代码和此附加代码中添加确认存在性和唯一性的验证。许多人还希望对Contact用于填充表单选择下拉列表的集合进行排序。
（注意：由于嵌套属性的使用导致在参数哈希中添加数字键（例如[“0”]），这取决于对象具有的那些嵌套属性类的关联记录的数量，我'已将hashie gem添加到 gem 文件中，它提供了在哈希中查找深层嵌套键的能力 via .deep_find，从而可以直接访问所需的键，绕过这些不同的数字键。）
模型（为表单选择下拉列表添加了联系类的方法）
def last_name_first
self.last_name + ', ' + self.first_name
end
控制器（已更新编辑和更新操作）
def edit
@contacts = Contact.all
@user.contacts.build
@user.user_contact_pairs.build
end
def update
@user = User.find(params[:id])
user_only_params = { email: params[:user][:email], first_name: params[:user][:first_name], last_name: params[:user][:last_name], username: params[:user][:username] }
contact_params = params[:user][:contacts_attributes]
user_contact_pair_params = params[:user][:user_contact_pairs_attributes]
contact_params.extend(Hashie::Extensions::DeepFind)
contact_first_name = contact_params.deep_find(:first_name)
contact_last_name = contact_params.deep_find(:last_name)
user_contact_pair_params.extend(Hashie::Extensions::DeepFind)
user_contact_pair_contact_id = user_contact_pair_params.deep_find(:contact_id)
user_contact_pair_order_number = user_contact_pair_params.deep_find(:order_number)
@user.assign_attributes(user_only_params)
if user_contact_pair_order_number != ''
if contact_first_name != '' && contact_last_name != ''
@contact = Contact.create(first_name: contact_first_name, last_name: contact_last_name)
@user.user_contact_pairs.new(contact_id: @contact.id, order_number: user_contact_pair_order_number.to_i)
elsif user_contact_pair_contact_id != ''
@user.user_contact_pairs.new(contact_id: user_contact_pair_contact_id.to_i, order_number: user_contact_pair_order_number.to_i)
end
end
respond_to do |format|
if @user.save
format.html { redirect_to @user, notice: 'User was successfully updated.' }
format.json { render :show, status: :ok, location: @user }
else
@contact.destroy if @contact.exists?
format.html { render :edit }
format.json { render json: @user.errors, status: :unprocessable_entity }
end
end
end
查看（用户/_form.html.erb）
<%= form_for(@user) do |user_form| %>
<% if @user.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@user.errors.count, "error") %> prohibited this user from being saved:</h2>
<ul>
<% @user.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="user">
<h2 style="margin-bottom: 4px">User</h2>
<%= user_form.label :email %><br>
<%= user_form.email_field :email %><br><br>
<%= user_form.label :first_name %><br>
<%= user_form.text_field :first_name %><br><br>
<%= user_form.label :last_name %><br>
<%= user_form.text_field :last_name %><br><br>
<%= user_form.label :username %><br>
<%= user_form.text_field :username %><br><br>
</div>
<%= user_form.fields_for :user_contact_pairs do |ucp_fields| %>
<% if ucp_fields.object.new_record? %>
<h2 style="margin-bottom: 4px">Use Existing Contact</h2>
<%= ucp_fields.collection_select(:contact_id, @contacts, :id, :last_name_first, prompt: "Select...") %><br><br>
<% end %>
<% end %>
<%= user_form.fields_for :contacts do |contact_fields| %>
<% if contact_fields.object.new_record? %>
<h2 style="margin-bottom: 4px">Or Create New Contact</h2>
<%= contact_fields.label 'First Name' %><br>
<%= contact_fields.text_field :first_name %><br><br>
<%= contact_fields.label 'Last Name' %><br>
<%= contact_fields.text_field :last_name %><br><br>
<% end %>
<% end %>
<%= user_form.fields_for :user_contact_pairs do |ucp_fields| %>
<% if ucp_fields.object.new_record? %>
<h2 style="margin-bottom: 4px">Order</h2>
<%= ucp_fields.label 'Order Number' %><br>
<%= ucp_fields.number_field :order_number %><br><br>
<% end %>
<% end %>
<div class="actions">
<%= user_form.submit %>
</div>
<% end %>