Mapeando relacionamentos

Mapeando relacionamentos

Nós conseguimos mapear nossas tabelas do banco de dados no Ecto através da macro Ecto.Schema

Mapeando relacionamentos nos schemas

1:1

defmodule EctoExample.Hospital.Schemas.Patient do
  use Ecto.Schema

  alias EctoExample.Hospital.Schemas.Room

  schema "patients" do
    field(:first_name, :string)
    field(:last_name, :string)

    has_one(:room, Room)

    timestamps()
  end
end

defmodule EctoExample.Hospital.Schemas.Room do
  use Ecto.Schema

  alias EctoExample.Hospital.Schemas.Patient

  schema "rooms" do
    field(:floor, :string)
    field(:number, :string)

    belongs_to(:patient, Patient)

    timestamps()
  end
end

mix ecto.gen.migration create_patients -r EctoExample.Hospital.Repo

defmodule EctoExample.Hospital.Repo.Migrations.CreatePatients do
  use Ecto.Migration

  def change do
    create table("patients") do
      add(:first_name, :string)
      add(:last_name, :string)
      timestamps()
    end
  end
end

mix ecto.gen.migration create_rooms -r EctoExample.Hospital.Repo

defmodule EctoExample.Hospital.Repo.Migrations.CreateRooms do
  use Ecto.Migration

  def change do
    create table("rooms") do
      add(:floor, :string)
      add(:number, :string)
      timestamps()
    end
  end
end

1:n

defmodule EctoExample.Hospital.Schemas.Driver do
  use Ecto.Schema

  alias EctoExample.DriverLicenses.Schemas.License

  schema "drivers" do
    field(:first_name, :string)
    field(:last_name, :string)

    has_many(:licenses, License)

    timestamps()
  end
end

defmodule EctoExample.Hospital.Schemas.License do
  use Ecto.Schema

  alias EctoExample.DriverLicenses.Schemas.Driver

  schema "licenses" do
    field(:type, :string)
    field(:digits, :string)

    belongs_to(:driver, Driver)

    timestamps()
  end
end

mix ecto.gen.migration create_drivers -r EctoExample.DriverLicenses.Repo

defmodule EctoExample.DriverLicenses.Repo.Migrations.CreateDrivers do
  use Ecto.Migration

  def change do
    create table("drivers") do
      add(:first_name, :string)
      add(:last_name, :string)
      timestamps()
    end
  end
end

mix ecto.gen.migration create_licenses -r EctoExample.DriverLicenses.Repo

defmodule EctoExample.DriverLicenses.Repo.Migrations.CreateLicenses do
  use Ecto.Migration

  def change do
    create table("licenses") do
      add(:type, :string)
      add(:digits, :string)
      timestamps()
    end
  end
end

n:n

defmodule EctoExample.MovieReviews.Schemas.Movie do
  use Ecto.Schema

  alias EctoExample.MovieReviews.Schemas.Rating

  schema "movies" do
    field(:title, :string)
    field(:director, :string)
    field(:year, :integer)

    has_many(:ratings, Rating)

    timestamps()
  end
end

defmodule EctoExample.MovieReviews.Schemas.Reviewer do
  use Ecto.Schema

  alias EctoExample.MovieReviews.Schemas.Rating

  schema "reviewers" do
    field(:name, :string)

    has_many(:ratings, Rating)

    timestamps()
  end
end

defmodule EctoExample.MovieReviews.Schemas.Rating do
  use Ecto.Schema

  alias EctoExample.MovieReviews.Schemas.Movie
  alias EctoExample.MovieReviews.Schemas.Reviewer

  schema "ratings" do
    field(:stars, :integer)

    belongs_to(:movie, Movie)
    belongs_to(:reviewer, Reviewer)

    timestamps()
  end
end

mix ecto.gen.migration create_movies -r EctoExample.MovieReviews.Repo

defmodule EctoExample.MovieReviews.Repo.Migrations.CreateMovies do
  use Ecto.Migration

  def change do
    create table("movies") do
      add(:title, :string)
      add(:director, :string)
      add(:year, :integer)
      timestamps()
    end
  end
end

mix ecto.gen.migration create_reviewers -r EctoExample.MovieReviews.Repo

defmodule EctoExample.MovieReviews.Repo.Migrations.CreateReviewers do
  use Ecto.Migration

  def change do
    create table("reviewers") do
      add(:name, :string)
      timestamps()
    end
  end
end

mix ecto.gen.migration create_ratings -r EctoExample.MovieReviews.Repo

defmodule EctoExample.MovieReviews.Repo.Migrations.CreateRatings do
  use Ecto.Migration

  def change do
    create table("ratings") do
      add(:stars, :integer)
      timestamps()
    end
  end
end

Mapeando relacionamentos nas tabelas

1:1

mix ecto.gen.migration add_patient_id_to_rooms -r EctoExample.Hospital.Repo

defmodule EctoExample.Hospital.Repo.Migrations.AddPatientIdToRooms do
  use Ecto.Migration

  def change do
    alter table("rooms") do
      add(:patient_id, references("patients"))
    end
  end
end

1:n

mix ecto.gen.migration add_driver_id_to_licenses -r EctoExample.DriverLicenses.Repo

defmodule EctoExample.DriverLicenses.Repo.Migrations.AddDriverIdToLicenses do
  use Ecto.Migration

  def change do
    alter table("licenses") do
      add(:driver_id, references("drivers"))
    end
  end
end

n:n

mix ecto.gen.migration add_relationships_to_rating -r EctoExample.MovieReviews.Repo

defmodule EctoExample.MovieReviews.Repo.Migrations.AddRelationshipsToRatings do
  use Ecto.Migration

  def change do
    alter table("ratings") do
      add(:movie_id, references("movies"))
      add(:reviewer_id, references("reviewers"))
    end
  end
end

Executar migrations para criar relacionamento entre tabelas

mix ecto.migrate -r EctoExample.MovieReviews.Repo

EctoExample.MovieReviews.Repo.query!("select * from schema_migrations")

mix ecto.migrations -r EctoExample.MovieReviews.Repo

Revertendo versões do banco de dados

mix ecto.rollback -r EctoExample.MovieReviews.Repo

EctoExample.MovieReviews.Repo.query!("select * from schema_migrations")

mix ecto.migrations -r EctoExample.MovieReviews.Repo

Referências

• Database migration: Concepts and principles (Part 1) - https://cloud.google.com/architecture/database-migration-concepts-principles-part-1
• Ecto.Migration - https://hexdocs.pm/ecto_sql/Ecto.Migration.html
• Change - https://hexdocs.pm/ecto_sql/Ecto.Migration.html#module-change
• Associations - https://hexdocs.pm/ecto/Ecto.html#module-associations
• belongs_to/3 - https://hexdocs.pm/ecto/Ecto.Schema.html#belongs_to/3
• has_many/3 - https://hexdocs.pm/ecto/Ecto.Schema.html#has_many/3
• has_one/3 - https://hexdocs.pm/ecto/Ecto.Schema.html#has_one/3