将嵌套属性添加到R​​ails中的关联模型

Question

I have three models using Active Record associations:

Book Model
has_many :checkouts

User Model
has_many :checkouts

Checkout Model
belongs_to :book
belongs_to :user

In my view, I need the book, checkout, and user names from the checkouts.

By using Book.first.checkouts I get:

#<ActiveRecord::AssociationRelation
  [#<Checkout id: 30,
    checkout_date: "2017-04-13",
    return_date: nil,
    book_id: 118,
    user_id: 1,
    created_at: "2017-04-13 17:43:07",
    updated_at: "2017-04-13 17:43:07"
  >,#<Checkout id: 50,
    checkout_date: "2017-04-13",
    return_date: nil,
    book_id: 118,
    user_id: 1,
    created_at: "2017-04-14 00:33:34",
    updated_at: "2017-04-14 00:33:34">
  ]>

But, I would like to the user name, not just the id. I've tried Book.first.checkouts.map { |c| c.user.name } Book.first.checkouts.map { |c| c.user.name } but that returns only the name, and I need the rest of the checkout information. Ideally, my data (converted to json) looks something like:

{
  name: "Book Name",
  checkouts:  [
    checkout_data: "Today",
    user_name: "Mary"
  ]
}

How can I add the user name to my checkout data?

Answer 1

您可以在控制器上尝试：

render json: @books, include: { checkout: { only: :checkout_date, include: { user: { only: :name } } }}

Answer 2

You should preload the data to prevent (N+1) query problem, For Display possible checkouts for particular book:

book_id = <given book id>
book = Book.find(book_id)
checkouts = book.checkouts.includes(:user)
return_hash = {name: book.name, checkouts: []}
checkouts.each do |checkout|
    return_hash[:checkouts] << { checkout_data: checkout.checkout_date,
                                 user_name: checkout.user.name
                               }
end

Answer 3

To include other solutions, I found this worked pretty well:

checkouts = book.checkouts.unreturned.map do |checkout|
  checkout.attributes.merge({ user_name: checkout.user.name })
end

{ checkouts: checkouts, available: book.available?, book_id: book.id }

attributes.merge did the trick.