Active Record 基础

class Book < ApplicationRecord
end

CREATE TABLE books (
  id int(11) NOT NULL auto_increment,
  title varchar(255),
  author varchar(255),
  PRIMARY KEY  (id)
);

$ bin/rails generate migration CreateBooks title:string author:string

# Note:
# The `id` column, as the primary key, is automatically created by convention.
# Columns `created_at` and `updated_at` are added by `t.timestamps`.

# db/migrate/20240220143807_create_books.rb
class CreateBooks < ActiveRecord::Migration[8.0]
  def change
    create_table :books do |t|
      t.string :title
      t.string :author

      t.timestamps
    end
  end
end

irb> book = Book.new
=> #<Book:0x00007fbdf5e9a038 id: nil, title: nil, author: nil, created_at: nil, updated_at: nil>

irb> book.title = "The Hobbit"
=> "The Hobbit"
irb> book.title
=> "The Hobbit"

$ bin/rails generate model Book::Order
      invoke  active_record
      create    db/migrate/20240306194227_create_book_orders.rb
      create    app/models/book/order.rb
      create    app/models/book.rb
      invoke    test_unit
      create      test/models/book/order_test.rb
      create      test/fixtures/book/orders.yml

$ bin/rails generate model Book::Order
      invoke  active_record
      create    db/migrate/20240305140356_create_book_orders.rb
      create    app/models/book/order.rb
    conflict    app/models/book.rb
  Overwrite /Users/bhumi/Code/rails_guides/app/models/book.rb? (enter "h" for help) [Ynaqdhm]

# app/models/book.rb
module Book
  def self.table_name_prefix
    "book_"
  end
end

# app/models/book/order.rb
class Book::Order < ApplicationRecord
end

# app/models/book.rb
class Book < ApplicationRecord
  # existing code
end

Book::Order.table_name
# => "book_orders"

class Book < ApplicationRecord
  self.table_name = "my_books"
end

# test/models/book_test.rb
class BookTest < ActiveSupport::TestCase
  set_fixture_class my_books: Book
  fixtures :my_books
  # ...
end

class Book < ApplicationRecord
  self.primary_key = "book_id"
end

book = Book.create(title: "The Lord of the Rings", author: "J.R.R. Tolkien")

# Note that the `id` is assigned as this record is committed to the database.
book.inspect
# => "#<Book id: 106, title: \"The Lord of the Rings\", author: \"J.R.R. Tolkien\", created_at: \"2024-03-04 19:15:58.033967000 +0000\", updated_at: \"2024-03-04 19:15:58.033967000 +0000\">"

book = Book.new
book.title = "The Hobbit"
book.author = "J.R.R. Tolkien"

# Note that the `id` is not set for this object.
book.inspect
# => "#<Book id: nil, title: \"The Hobbit\", author: \"J.R.R. Tolkien\", created_at: nil, updated_at: nil>"

# The above `book` is not yet saved to the database.

book.save
book.id # => 107

# Now the `book` record is committed to the database and has an `id`.

book = Book.new do |b|
  b.title = "Metaprogramming Ruby 2"
  b.author = "Paolo Perrotta"
end

book.save

/* Note that `created_at` and `updated_at` are automatically set. */

INSERT INTO "books" ("title", "author", "created_at", "updated_at") VALUES (?, ?, ?, ?) RETURNING "id"  [["title", "Metaprogramming Ruby 2"], ["author", "Paolo Perrotta"], ["created_at", "2024-02-22 20:01:18.469952"], ["updated_at", "2024-02-22 20:01:18.469952"]]

# Return a collection with all books.
books = Book.all

# Return a single book.
first_book = Book.first
last_book = Book.last
book = Book.take

-- Book.all
SELECT "books".* FROM "books"

-- Book.first
SELECT "books".* FROM "books" ORDER BY "books"."id" ASC LIMIT ?  [["LIMIT", 1]]

-- Book.last
SELECT "books".* FROM "books" ORDER BY "books"."id" DESC LIMIT ?  [["LIMIT", 1]]

-- Book.take
SELECT "books".* FROM "books" LIMIT ?  [["LIMIT", 1]]

# Returns the first book with a given title or `nil` if no book is found.
book = Book.find_by(title: "Metaprogramming Ruby 2")

# Alternative to Book.find_by(id: 42). Will throw an exception if no matching book is found.
book = Book.find(42)

-- Book.find_by(title: "Metaprogramming Ruby 2")
SELECT "books".* FROM "books" WHERE "books"."title" = ? LIMIT ?  [["title", "Metaprogramming Ruby 2"], ["LIMIT", 1]]

-- Book.find(42)
SELECT "books".* FROM "books" WHERE "books"."id" = ? LIMIT ?  [["id", 42], ["LIMIT", 1]]

# Find all books by a given author, sort by created_at in reverse chronological order.
Book.where(author: "Douglas Adams").order(created_at: :desc)

SELECT "books".* FROM "books" WHERE "books"."author" = ? ORDER BY "books"."created_at" DESC [["author", "Douglas Adams"]]

book = Book.find_by(title: "The Lord of the Rings")
book.title = "The Lord of the Rings: The Fellowship of the Ring"
book.save

book = Book.find_by(title: "The Lord of the Rings")
book.update(title: "The Lord of the Rings: The Fellowship of the Ring")

/* Note that `updated_at` is automatically set. */

 UPDATE "books" SET "title" = ?, "updated_at" = ? WHERE "books"."id" = ?  [["title", "The Lord of the Rings: The Fellowship of the Ring"], ["updated_at", "2024-02-22 20:51:13.487064"], ["id", 104]]

Book.update_all(status: "already own")

book = Book.find_by(title: "The Lord of the Rings")
book.destroy

DELETE FROM "books" WHERE "books"."id" = ?  [["id", 104]]

# Find and delete all books by Douglas Adams.
Book.destroy_by(author: "Douglas Adams")

# Delete all books.
Book.destroy_all

class User < ApplicationRecord
  validates :name, presence: true
end

irb> user = User.new
irb> user.save
=> false
irb> user.save!
ActiveRecord::RecordInvalid: Validation failed: Name can't be blank

irb> user = User.create
=> #<User:0x000000013e8b5008 id: nil, name: nil>
irb> user.errors.full_messages
=> ["Name can't be blank"]

class User < ApplicationRecord
  after_create :log_new_user

  private
    def log_new_user
      puts "A new user was registered"
    end
end

irb> @user = User.create
A new user was registered

class CreatePublications < ActiveRecord::Migration[8.0]
  def change
    create_table :publications do |t|
      t.string :title
      t.text :description
      t.references :publication_type
      t.references :publisher, polymorphic: true
      t.boolean :single_issue

      t.timestamps
    end
  end
end

class Author < ApplicationRecord
  has_many :books
end