Add nested attribute to associated model in Rails

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 } 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?

Are you displaying the checkouts individually, i.e. an .each loop? You should be able to display checkout.user.name — Okomikeruko
– Okomikeruko, Commented Apr 25, 2017 at 17:44
@Okomikeruko yes, individually through an each loop. checkout.user.name works, but it only returns the user name. I need both the checkout and the user name. I'm wondering if I can add it to a virtual attribute, or something like that. — bholtbholt
– bholtbholt, Commented Apr 25, 2017 at 17:48
I guess I'm trying to combine the data of 2 objects: checkouts and user — bholtbholt
– bholtbholt, Commented Apr 25, 2017 at 17:54
Are you saying you want checkout.username to do the same thing as checkout.user.name? — Okomikeruko
– Okomikeruko, Commented Apr 25, 2017 at 18:11
If the goal is to optimize your JSON output, this thread had some answers regarding that: stackoverflow.com/questions/13678092/… — Okomikeruko
– Okomikeruko, Commented Apr 25, 2017 at 18:13

Ruby Junior Dev · Accepted Answer · 2017-04-25 19:48:26Z

1

You can try this at your controller:

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

edited Apr 25, 2017 at 19:48

answered Apr 25, 2017 at 18:26

Ruby Junior Dev

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1 Comment

bholtbholt Over a year ago

Didn't know about this! It's really nice

aqfaridi · Accepted Answer · 2017-04-25 19:00:07Z

0

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

answered Apr 25, 2017 at 19:00

aqfaridi

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2 Comments

bholtbholt Over a year ago

This is kind of what I was trying out, but I wondered if there was a simpler way. What's the N+1 query problem?

aqfaridi Over a year ago

checkout.user will fire 1 query to database for each checkout, if you use includes :user then all the corresponding users will be pre fetched in single IN query

bholtbholt · Accepted Answer · 2017-04-25 23:26:53Z

0

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.

answered Apr 25, 2017 at 23:26

bholtbholt

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1 Comment

aqfaridi Over a year ago

Dont use. attributes.merge in a loop, it will take hell lot of execution time as your application grows, i faced the same performance issue in my application, use ruby-prof to see the bottleneck in your code

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