4 replies

How to autoload a relationship?

Stefan Wintermeyer · 2023-09-20T12:16:40.203Z

The setup: **lib/app/shop/resources/product.ex** ```elixir defmodule App.Shop.Product do [...] relationships do belongs_to :category, App.Shop.Category do attribute_writable? true end end [...] end ``` I want to query for the product "Banana": ```elixir iex(12)> fruits = App.Shop.Category.create!(%{name: "Fruits"}) #App.Shop.Category , id: "3a3ed806-6df4-4602-aff6-4eed50e814b2", name: "Fruits", ... > iex(13)> banana = App.Shop.Product.create!(%{name: "Banana", price: 0.1, category_id: fruits.id}) #App.Shop.Product , category: #Ash.NotLoaded , __meta__: #Ecto.Schema.Metadata , id: "d655fa01-ece5-4ad9-b927-764a6a48b165", name: "Banana", price: Decimal.new("0.1"), category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2", ... > iex(14)> App.Shop.Product.by_name("Banana") {:ok, #App.Shop.Product , category: #Ash.NotLoaded , __meta__: #Ecto.Schema.Metadata , id: "d655fa01-ece5-4ad9-b927-764a6a48b165", name: "Banana", price: Decimal.new("0.1"), category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2", ... >} iex(15)> App.Shop.load(banana, :category) {:ok, #App.Shop.Product , category: #App.Shop.Category , id: "3a3ed806-6df4-4602-aff6-4eed50e814b2", name: "Fruits", ... >, __meta__: #Ecto.Schema.Metadata , id: "d655fa01-ece5-4ad9-b927-764a6a48b165", name: "Banana", price: Decimal.new("0.1"), category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2", ... >} ``` **Question:** How can I autoload the `category` when I query for a `product` so that I don't have to do two SQL requests? `App.Shop.Product.by_name("Banana")` should get me the `product` and the `category`.

The setup:

lib/app/shop/resources/product.ex

defmodule App.Shop.Product do
  [...]
  relationships do
    belongs_to :category, App.Shop.Category do
      attribute_writable? true
    end
  end
  [...]
end

defmodule App.Shop.Product do
  [...]
  relationships do
    belongs_to :category, App.Shop.Category do
      attribute_writable? true
    end
  end
  [...]
end

defmodule App.Shop.Product do
  [...]
  relationships do
    belongs_to :category, App.Shop.Category do
      attribute_writable? true
    end
  end
  [...]
end

defmodule App.Shop.Product do
  [...]
  relationships do
    belongs_to :category, App.Shop.Category do
      attribute_writable? true
    end
  end
  [...]
end

I want to query for the product "Banana":

iex(12)> fruits = App.Shop.Category.create!(%{name: "Fruits"})
#App.Shop.Category<
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  name: "Fruits",
  ...
>
iex(13)> banana = App.Shop.Product.create!(%{name: "Banana", price: 0.1, category_id: fruits.id})
#App.Shop.Product<
  promotion: #Ash.NotLoaded<:relationship>,
  category: #Ash.NotLoaded<:relationship>,
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
  name: "Banana",
  price: Decimal.new("0.1"),
  category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  ...
>
iex(14)> App.Shop.Product.by_name("Banana")
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #Ash.NotLoaded<:relationship>,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}
iex(15)> App.Shop.load(banana, :category)
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #App.Shop.Category<
     __meta__: #Ecto.Schema.Metadata<:loaded>,
     id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
     name: "Fruits",
     ...
   >,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}

iex(12)> fruits = App.Shop.Category.create!(%{name: "Fruits"})
#App.Shop.Category<
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  name: "Fruits",
  ...
>
iex(13)> banana = App.Shop.Product.create!(%{name: "Banana", price: 0.1, category_id: fruits.id})
#App.Shop.Product<
  promotion: #Ash.NotLoaded<:relationship>,
  category: #Ash.NotLoaded<:relationship>,
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
  name: "Banana",
  price: Decimal.new("0.1"),
  category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  ...
>
iex(14)> App.Shop.Product.by_name("Banana")
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #Ash.NotLoaded<:relationship>,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}
iex(15)> App.Shop.load(banana, :category)
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #App.Shop.Category<
     __meta__: #Ecto.Schema.Metadata<:loaded>,
     id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
     name: "Fruits",
     ...
   >,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}

iex(12)> fruits = App.Shop.Category.create!(%{name: "Fruits"})
#App.Shop.Category<
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  name: "Fruits",
  ...
>
iex(13)> banana = App.Shop.Product.create!(%{name: "Banana", price: 0.1, category_id: fruits.id})
#App.Shop.Product<
  promotion: #Ash.NotLoaded<:relationship>,
  category: #Ash.NotLoaded<:relationship>,
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
  name: "Banana",
  price: Decimal.new("0.1"),
  category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  ...
>
iex(14)> App.Shop.Product.by_name("Banana")
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #Ash.NotLoaded<:relationship>,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}
iex(15)> App.Shop.load(banana, :category)
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #App.Shop.Category<
     __meta__: #Ecto.Schema.Metadata<:loaded>,
     id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
     name: "Fruits",
     ...
   >,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}

iex(12)> fruits = App.Shop.Category.create!(%{name: "Fruits"})
#App.Shop.Category<
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  name: "Fruits",
  ...
>
iex(13)> banana = App.Shop.Product.create!(%{name: "Banana", price: 0.1, category_id: fruits.id})
#App.Shop.Product<
  promotion: #Ash.NotLoaded<:relationship>,
  category: #Ash.NotLoaded<:relationship>,
  __meta__: #Ecto.Schema.Metadata<:loaded>,
  id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
  name: "Banana",
  price: Decimal.new("0.1"),
  category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
  ...
>
iex(14)> App.Shop.Product.by_name("Banana")
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #Ash.NotLoaded<:relationship>,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}
iex(15)> App.Shop.load(banana, :category)
{:ok,
 #App.Shop.Product<
   promotion: #Ash.NotLoaded<:relationship>,
   category: #App.Shop.Category<
     __meta__: #Ecto.Schema.Metadata<:loaded>,
     id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
     name: "Fruits",
     ...
   >,
   __meta__: #Ecto.Schema.Metadata<:loaded>,
   id: "d655fa01-ece5-4ad9-b927-764a6a48b165",
   name: "Banana",
   price: Decimal.new("0.1"),
   category_id: "3a3ed806-6df4-4602-aff6-4eed50e814b2",
   ...
 >}

Question: How can I autoload the

category

category

category

category when I query for a

product

product

product

product so that I don't have to do two SQL requests?

App.Shop.Product.by_name("Banana")

App.Shop.Product.by_name("Banana")

App.Shop.Product.by_name("Banana")

App.Shop.Product.by_name("Banana") should get me the

product

product

product

product and the

category

category

category

category.

How to autoload a relationship?

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