Rails: include nested through association

Question

I have a Store model, which has an id and other fields. I have a Product model which has an id and other field To join them I use Amount model. Here are the models:

class Product < ApplicationRecord
    has_many :amounts
    has_many :stores, through: :amounts
end

class Store < ApplicationRecord
    has_many :amounts
    has_many :products  , through: :amounts
end

class Amount < ApplicationRecord
    belongs_to :store
    belongs_to :product
end

Amount has in_stock property. I want my json to look like this:

{stores: [
    {"id": 1,
     "name": "New Store",
     "products": ["id": 1, "name": "Toothbrush", "in_stock": 4000]}
]}

I tried render json: {stores: stores}.to_json(include: :products), I also tried a nested include but it didn't work as well, it showed output for all amounts

SteveTurczyn · Accepted Answer · 2017-12-21 13:26:19Z

2

Based on your comments on my original answer (which shows in stock comes from the Amount model) you can include amounts in the includes relation which would be a cleaner solution and more performant...

output = Store.all.includes(amounts: :product).map do |store|

  { id: store.id, name: store.name,
    products: store.amounts.map do |amount|
     { id: amount.product.id, name: amount.product.name, in_stock: amount._in_stock }
    end
  }

end.to_json

answered Dec 21, 2017 at 13:26

SteveTurczyn

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SteveTurczyn · Accepted Answer · 2017-12-21 12:21:26Z

2

output = Store.all.includes(:products).map do |store|

  { id: store.id, name: store.name,
    products: store.products.map do |product|
     { id: product.id, name: product.name, in_stock: product.in_stock }
    end
  }

end.to_json

This builds an array of store hashes, each store hash has an array of products, and the hash is converted to json.

answered Dec 21, 2017 at 12:21

SteveTurczyn

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2 Comments

alt-ja Over a year ago

there's no method in_stock for product

alt-ja Over a year ago

This works, but { id: product.id, name: product.name, in_stock: store.amounts .where(:product_id => product.id) .first ._in_stock } end } `

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