在 Rails 中，如何使用 accepts_nested_attributes_for 创建嵌套对象? [英] In Rails, how do I create nested objects using accepts_nested_attributes_for?

问题描述

在我的 Rails 应用程序中，我试图为 TrainingClass 模型设置创建表单.我希望这个表单允许用户在同一个表单中创建多个 ClassMeeting 模型(它们与 TrainingClass 模型具有belongs_to 关系)，我正在使用 接受_nested_attributes_for 来做到这一点.不幸的是，每当我提交表单时，我都会收到错误消息:Meetings class can't be blank.

In my Rails application, I am attempting to set up creation form for a TrainingClass model. I want this form to allow the user to create multiple ClassMeeting models (which have a belongs_to relationship with the TrainingClass model) within the same form, and I am using accepts_nested_attributes_for to do this. Unfortunately, whenever I submit the form I get the error message: Meetings class can't be blank.

我意识到这是因为 ClassMeeting 有 validates :class_id,presence: true，并且因为 TrainingClass 直到保存后，但我不确定解决此问题的正确方法.(我可以想到几种可能的方法，但它们并不是完全优雅的解决方案.)有什么想法吗?如果您能给我任何帮助，我将不胜感激.

I realize that this is because ClassMeeting has validates :class_id, presence: true, and because TrainingClass can't have an id until after it is saved, but I'm not sure of the right way to get around this. (I can think of a few possible ways, but they aren't exactly elegant solutions.) Any ideas? I'd appreciate any help you can give me.

注意:我意识到过去有人问过很多类似的问题.然而，这些问题中的大多数都是陈旧的，而且答案已经过时，而且没有一个能解决我的问题.

这是我的代码.请记住，虽然为了简洁起见我已经简化了它的某些方面，但是 ClassMeeting 和 TrainingClass 模型之间的关系没有受到影响:

Here is my code. Keep in mind that although I have simplified some aspects of it for brevity, the relationship between the ClassMeeting and TrainingClass models was left untouched:

ClassMeeting 模型:

# == Schema Information
#
# Table name: class_meetings
#
#  id         :integer         not null, primary key
#  class_id   :integer
#  start      :datetime
#  end        :datetime
#  location   :string(255)
#  created_at :datetime        not null
#  updated_at :datetime        not null
#

class ClassMeeting < ActiveRecord::Base
  attr_accessible :start, :end, :location

  validates :class_id, presence: true
  validates :start, presence: true
  validates :end, presence: true
  validates :location, presence: true, length: {maximum: 255}

  belongs_to :training_class, foreign_key: :class_id, inverse_of: :meetings
end

培训班模型:

# == Schema Information
#
# Table name: training_classes
#
#  id            :integer         not null, primary key
#  description   :string(255)
#  created_at    :datetime        not null
#  updated_at    :datetime        not null
#

class TrainingClass < ActiveRecord::Base
  attr_accessible :description, :meetings_attributes

  validates :description, length: {maximum: 255}

  has_many :meetings, class_name: :ClassMeeting, foreign_key: :class_id, inverse_of: :training_class

  accepts_nested_attributes_for :meetings, allow_destroy: true
end

TrainingClasses 控制器:

class TrainingClassesController < ApplicationController
  def new
    @training_class = TrainingClass.new()
    @training_class.meetings.build
  end

  def create
    @training_class = TrainingClass.new()

    if @training_class.update_attributes(params[:training_class])
        redirect_to @training_class, notice: 'Class was successfully created.'
    else
        render "new"
    end
  end
end

培训班表格(查看):

<%= form_for @training_class do |f| %>
    <%= render 'shared/error_messages', object: f.object %>

    <%= f.text_area :description %>

    <h2>Schedule</h2>
    <%= f.fields_for :meetings do |meeting| %>
        <%= meeting.label :start, "Start of Meeting:" %>
        <%= meeting.text_field :start %>

        <%= meeting.label :end, "End of Meeting:" %>
        <%= meeting.text_field :end %>

        <%= meeting.label :location, "Location:" %>
        <%= meeting.text_field :location %>
    <% end %>

    <%= f.submit class:"btn btn-large btn-primary" %>
<% end %>

推荐答案

好的，我找到了问题的解决方案.我需要做的就是验证 ClassMeeting 模型中是否存在 training_class 而不是 class_id.这样，训练类的存在仍然被验证，但验证器不会干扰 accepts_nested_attributes_for 保存模型的方法:

All right, I found the solution to my problem. All I need to do is validate the presence of training_class instead of class_id in the ClassMeeting model. That way the existence of a training class is still validated, but the validator doesn't interfere with accepts_nested_attributes_for's method of saving the model:

class ClassMeeting < ActiveRecord::Base
  attr_accessible :start, :end, :location

  validates :training_class, presence: true # :training_class instead of :class_id
  validates :start, presence: true
  validates :end, presence: true
  validates :location, presence: true, length: {maximum: 255}

  belongs_to :training_class, foreign_key: :class_id, inverse_of: :meetings
end

这篇关于在 Rails 中，如何使用 accepts_nested_attributes_for 创建嵌套对象?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！