RoR: database level referential integrity - ruby-on-rails

Question

I have this model:
class Book < ApplicationRecord
has_many :pages, dependent: :destroy
end
And this one:
class Page < ApplicationRecord
belongs_to :book
end
The migration for the Book is:
class CreateBooks < ActiveRecord::Migration[5.0]
def change
create_table :books do |t|
end
end
end
And the migration for Page is:
class CreatePages < ActiveRecord::Migration[5.0]
def change
create_table :pages do |t|
t.references :book, index: true, null: false
end
end
add_foreign_key :pages, :books, on_delete: :cascade
end
Additionally I got some seeds:
Book.create!(
pages: [
Page.new,
Page.new,
Page.new
]
)
rake db:migrate, rake db:seed and all that jazz. I jump into rails c:
Book.first
Book Load (0.1ms) SELECT "books".* FROM "books" ORDER BY "books"."id" ASC LIMIT ? [["LIMIT", 1]]
=> #<Book id: 1>
Cool....now?
Page.count
(0.3ms) SELECT COUNT(*) FROM "pages"
=> 3
Makes total sense. Next:
Book.first.destroy
Book Load (0.2ms) SELECT "books".* FROM "books" ORDER BY "books"."id" ASC LIMIT ? [["LIMIT", 1]]
(0.1ms) begin transaction
Page Load (0.1ms) SELECT "pages".* FROM "pages" WHERE "pages"."book_id" = ? [["book_id", 1]]
SQL (0.1ms) DELETE FROM "pages" WHERE "pages"."id" = ? [["id", 1]]
SQL (0.0ms) DELETE FROM "pages" WHERE "pages"."id" = ? [["id", 2]]
SQL (0.0ms) DELETE FROM "pages" WHERE "pages"."id" = ? [["id", 3]]
SQL (0.1ms) DELETE FROM "books" WHERE "books"."id" = ? [["id", 1]]
Yay! Almost there...after seeding again I do this:
Book.first.delete
Book Load (0.1ms) SELECT "books".* FROM "books" ORDER BY "books"."id" ASC LIMIT ? [["LIMIT", 1]]
SQL (144.0ms) DELETE FROM "books" WHERE "books"."id" = ? [["id", 2]]
WTF?
Page.count
(0.1ms) SELECT COUNT(*) FROM "pages"
=> 3
I know delete does not trigger callbacks, so that dependent: :destroy won't help me here. But the foreign key? Hello? I want referential integrity in my database level!! What am I doing wrong? I've tried more things, like moving the on_delete: :cascade to the field definition:
def change
create_table :pages do |t|
t.references :book, index: true, null: false
end
end
But...nope, same result. I've searched and read the ActiveRecord documentation twice, and a few other questions in SO pointed me to my current setup (which is not the project I'm working on, but rather a newly generated one with the same basic configuration to replicate the error - yea, it fails there too), but I just can't put my finger on what's wrong. Perhaps it's just too late and I'm getting too tired. Help? Does Rails even support this? I'm using v5, far, far ahead of 4.2 where the constraints at db level were integrated. My db/schema.rb looks like this:
ActiveRecord::Schema.define(version: 20160218232358) do
create_table "books", force: :cascade do |t|
end
create_table "pages", force: :cascade do |t|
t.integer "book_id", null: false
t.index ["book_id"], name: "index_pages_on_book_id"
end
end
No trace of foreign keys?

Answer 1

For you're testing you are probably using SQLite, here only mysql, mysql2 and postgres are mentioned therefore I think rails does not support foreign keys on SQLite: http://edgeguides.rubyonrails.org/4_2_release_notes.html#foreign-key-support
It is also stated in another so post: https://stackoverflow.com/a/28801481/4560144