如何在保存Rails 4之前检查现有记录？

Question

I'm currently working on a simple Rails 4 app where I have these two related models:

book.rb

class Book < ActiveRecord::Base
  belongs_to :author

  accepts_nested_attributes_for :author
end

author.rb

class Author < ActiveRecord::Base
  has_many :books
end

What I need to do is to check if the author exists already and if it does, use it on the book.

My books_controller.rb

class BooksController < ApplicationController
  .
  .
  .
  def create
    @book = Book.new(BookParams.build(params)) # Uses class for strong params 

    if @book.save
      redirect_to @book, notice: t('alerts.success')
    else
      render action: 'new'
    end
  end
end

Is there a better way to deal with this scenario without having duplicate author records? Thank you.

Answer 1

You can do this using a before_save callback in the Book model:

class Book < ActiveRecord::Base
  # ...

  before_save :merge_author

  private

  def merge_author
    if (author = Author.find_by(name: self.author.name))
      self.author = author
    end
  end
end

Note here that I am assuming here that your Author model has a name field which identifies each author. Perhaps you want to have another mechanism to determine if the author already exists.

However, Active Record Validations can also help you ensure that you have no duplicated records in your Author model.

Answer 2

I might be misunderstanding but try to clearify the problem a little more please.

From my point of view you have to make sure yourself that you don't have duplicate records. In Rails you can use Validations in that case.

Rails Guides Validations

On the other hand what you are trying to solve looks like building/creating an ActiveRecord object through an ActiveRecord association. You have a Rails way for that, too.

Rails Guides Associations

Next there a callbacks, nested routes/controllers aso that fit to different requirements. You find Rails Guides for them, too. Of course it can be a combination of everything =) And you have nested attributes as well which might have to be considered. cheers

Answer 3

I've managed to make it work by using the code below:

models/book.rb

def author_attributes=(value)
  self.author = Author.find_or_create_by(value)
end