Can't insert MySQL query in Rails 5 (Lynda Course)

问题

I'm taking a course on Lynda.com (Ruby on Rails 5 Essential Training) and I'm having an issue with adding a record on a table. Here's some details: The objective is to create a joint table, Many-to-Many association, so we're first trying to create a record on with of the tables we want to use on the new table. And everytime I write this line:

section = Sections.create(:name => "Section One", :position => 1)

It gives me this

    (0.2ms)  BEGIN
   (0.3ms)  ROLLBACK
 => #<Section id: nil, page_id: nil, name: "Section One", position: 1, visible: false, content_type: nil, content: nil, created_at: nil, updated_at: nil>

I checked my code and everything seems fine. By the way inserting records on other tables works. It's just this table.

one important point, This table is a previously created table. It's the new one we're trying to create.

What am I doing wrong?

Here is my code from migrate:

class CreateSections < ActiveRecord::Migration[5.2]

  def up
    create_table :sections do |t|

      t.integer   "page_id"
      t.string    "name"
      t.integer   "position"
      t.boolean   "visible", :default => false
      t.string    "content_type"
      t.text      "content"
      t.timestamps
    end
    add_index("sections", "page_id")
  end

  def down
    drop_table :sections
  end


end

Here is the Section model:

class Section < ApplicationRecord

belongs_to :page
has_many :section_edits


end

回答1:

The error is caused by: belongs_to :page as the page_id is nil and by default Rails belongs_to helper is adding a presence validation to make sure that the association is valid.

To disable this behaviour (presence validation) you can use:

belongs_to :page, optional: true

as mentioned here: https://guides.rubyonrails.org/association_basics.html#options-for-belongs-to

or you can add page_id to your Section.create call as mentioned by others:

page_id = 1 # or Page.first.id or any page id you need
section = Section.create(name: "Section One", position: 1, page_id: page_id)

回答2:

Your error comes from belongs_to :page
If you try with create!, you should see this error message:

ActiveRecord::RecordInvalid: Validation failed: Page must exist

Just add page_id in your section creation:

page_id = 1 # or Page.first.id or any page id you need
section = Section.create(name: "Section One", position: 1, page_id: page_id)

来源：https://stackoverflow.com/questions/52078024/cant-insert-mysql-query-in-rails-5-lynda-course

标签

ruby-on-rails-5