Ecto Embedded Schemas

We’ll take a look at how Ecto’s embedded schemas can help us persist and retrieve structured and meaningful data using database JSON columns.

This is a lightning talk I gave at the May 2018 Montreal Elixir Meetup hosted by Mirego.

Transcript

1. Ecto Embedded Schemas
   Rémi Prévost Montreal Elixir Meetup
   2018/05/09
   

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3. params = %{
   "author_name" => "Rémi Prévost",
   "published" => true,
   "title" => %{
   "en" => "My new article in english",

   "fr" => "Mon nouvel article en français"
   }
   }
   %App.Blog.Article{}
   |> App.Blog.Article.changeset(params)
   |> App.Repo.insert!()
   

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4. Schema-less data
   Map → JSON → Map
   

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5. defmodule App.Blog.Article do
   use Ecto.Schema
   import Ecto.Changeset
   schema "articles" do
   field(:author_name, :string)
   field(:published, :boolean)
   field(:title, :map)
   end
   def changeset(%__MODULE__{} = record, params) do
   record
   |> cast(~w(author_name published title)a, params)
   |> validate_required(~w(author_name title)a)
   |> validate_change(:title, &validate_nested_french_value/2)
   end

   defp validate_nested_french_value(field, %{"fr" => fr}) when fr != "", do: []
   defp validate_nested_french_value(field, _) do
   [{field, "must specify french value"}]
   end
   end
   

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6. App.Blog.Article
   |> App.Repo.get(1)
   %App.Blog.Article{
   id: 1,
   author_name: "Rémi Prévost",
   published: true,
   title: %{
   en: "My new article in english",

   fr: "Mon nouvel article in english"
   }
   }
   

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7. defmodule App.Payments.Transaction do
   use Ecto.Schema
   import Ecto.Changeset
   schema "payment_transations" do
   field(:gateway_response, :map)
   belongs_to(:order_id, App.Order)
   end
   def changeset(%__MODULE__{} = record, params) do
   record
   |> cast(~w(order_id gateway_response)a, params)
   |> validate_required(~w(order_id)a)
   end
   end
   

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8. Embedded schema
   Schema → JSON → Schema
   

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9. defmodule App.Blog.Article do
   use Ecto.Schema
   import Ecto.Changeset
   schema "articles" do
   field(:author_name, :string)

   field(:published, :boolean)
   embeds_one(:title, App.Translations.Translated)
   end
   def changeset(%__MODULE__{} = record, params) do
   record
   |> cast(~w(author_name published)a, params)
   |> validate_required(~w(author_name)a)
   |> cast_embed(:title, required: true)
   end
   end
   

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10. defmodule App.Translations.Translated do
    use Ecto.Schema
    import Ecto.Changeset
    embedded_schema do
    field(:en, :string)
    field(:fr, :string)
    end
    def changeset(%__MODULE__{} = record, params) do
    record
    |> cast(~w(en fr)a, params)
    |> validate_required(~w(fr)a)
    end
    end
    

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11. App.Blog.Article
    |> App.Repo.get(1)
    %App.Blog.Article{
    id: 1,
    author_name: "Rémi Prévost",

    published: true,
    title: %App.Translations.Translated{
    id: "602975a2-bfbd-4c48-9d60-0b955ccc4bc7",
    en: "My new article in english",
    fr: "Mon nouvel article en français"
    }
    }
    

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12. That’s it!
    Ecto.Schema and Ecto.Changeset are awesome.
    

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