ActiveRecord :: NotNullViolation（PG :: NotNullViolation：错误：“ content_id”列中的空值违反了非空约束

Question

I'm currently building a rails 5 application in which a shout can be a TextShout or a PhotoShout . When creating a shout, content_id is not being pass in the params therefore raising a Not Null Value error. In the migration for the shout I can not find where the error is coming from. I have the following files.

show.html.erb

<%= form_for @shout do |form| %>
<%= form.hidden_field :content_type, value: "TextShout" %>
  <%= form.fields_for :content do |content_form| %>
    <%= content_form.text_field :body, placeholder: "shout here!", required: true %>
    <%= content_form.submit "Shout!" %>
    <% end %>
<% end %>

<%= form_for @shout do |form| %>
<%= form.hidden_field :content_type, value: "PhotoShout" %>
  <%= form.fields_for :content do |content_form| %>
    <%= content_form.file_field :image, required: true %>
    <%= content_form.submit "Shout!" %>
    <% end %>
<% end %>

<%= render @shouts %>

migration/_make_shouts_polymorphic.rb

class MakeShoutsPolymorphic < ActiveRecord::Migration[5.1]
  class Shout < ApplicationRecord
    belongs_to :content, polymorphic: true
  end
  class TextShout < ApplicationRecord; end
  def change
    change_table(:shouts) do |t|
      t.string :content_type
      t.integer :content_id
      t.index [:content_type, :content_id]
    end

    reversible do |dir|
      Shout.reset_column_information
      Shout.find_each do |shout|
        dir.up do
          text_shout = TextShout.create(body: shout.body)
          shout.update(content_id: text_shout.id, content_type: "TextShout")
        end
        dir.down do
          shout.update(body: shout.content.body)
          shout.content.destroy 
        end
      end
    end

    remove_column :shouts, :body, :string
  end
end

shouts_controller.rb

class ShoutsController < ApplicationController

  def show
    @shout = Shout.find(params[:id])
  end

  def create
    shout = current_user.shouts.create(shout_params)
    redirect_to root_path, redirect_options_for(shout)
  end

  private

  def shout_params
    { content: content_from_params }
  end

  def content_from_params
    case params[:shout][:content_type]
    when "TextShout" then TextShout.new(text_shout_content_params)
    when "PhotoShout" then PhotoShout.new(photo_shout_content_params)
    end
  end

  def text_shout_content_params
    params.require(:shout).require(:content).permit(:body)
  end

  def photo_shout_content_params
    params.require(:shout).require(:content).permit(:image)
  end

  def redirect_options_for(shout)
    if shout.persisted?
      {notice: "Shouted Successfully"}
    else
      {alert: "Could not shout"}
    end
  end
end

Answer 1

neither text_shout_content_params and photo_shout_content_params are permitting a content_id , but it looks like you're trying to (or at least you should be intending to) create one in your content_from_params

def content_from_params
  case params[:shout][:content_type]
    when "TextShout" 
      shout = TextShout.new(text_shout_content_params)
    when "PhotoShout"
      shout = PhotoShout.new(photo_shout_content_params)
  end
  shout.save!
  params[:shout][:content_id] = shout.id 
  params[:shout]
end

Answer 2

If you want the content to have an id you will have to create the shout using create instead of new . create will attempt to add a record to the database and will assign an id.

It may also be beneficial to use create! which will raise an error if the shout has invalid data and cannot be saved.

def content_from_params
  case params[:shout][:content_type]
  when "TextShout" then TextShout.create(text_shout_content_params)
  when "PhotoShout" then PhotoShout.create(photo_shout_content_params)
  end
end