Rails 3, how add a associated record after creating a primary record (Books, Auto Add BookCharacter)

Question

Rails newbie... trying to understand the right way to do things...

In my app users can create a Book ( I have that working)

What I want to happen is when a user

Answer 1

I prefer something like (if User has_many Book):

def create
 @book = current_user.books.new(params[:book])
 respond_to do |format|
  if @book.save
  …

Answer 2

The important thing to understand is the convention by which Rails implements relationships using ActiveRecord. A book has many characters, and each character belongs to a book, so:

class Book < ActiveRecordBase
  has_many :characters
end

class Character < ActiveRecordBase
  belongs_to :book
end

Rails now assumes that the characters table will have a foreign key called book_id, which relates to the books table. To create a character belonging to a book:

@book = Book.new(:name=>"Book name")
@character = @book.characters.build(:name=>"Character name")

Now when @book is saved (assuming both @book and @character are valid), a row will be created in both the books and the characters tables, with the character row linked through book_id.

To show that a character also belongs to a user, you could add that relationship to the Character model:

class Character < ActiveRecordBase
  belongs_to :book
  belongs_to :user
end

Thus Rails now expects characters to also have foreign key called user_id, which points to a users table (which also needs a User model). To specify the user when creating the character:

@book = Book.new(:name=>"Book name")
@character = @book.characters.build(:name=>"Character name",:user=>current_user)

You can also assign the foreign key by calling the corresponding method on the object:

@character.user = current_user

This all works because it follows the Rails conventions for naming models and tables. You can depart from these conventions, but you'll have a harder time learning Rails if you do.