20220319222511_create_groups.exs

# priv/repo/migrations/20220319222511_create_groups.exs

defmodule TestApp.Repo.Migrations.CreateGroups do
  use Ecto.Migration

  def change do
    create table(:groups) do
      add :name, :string, null: false
      add :region, :string, null: false
      add :score, :integer, null: false, default: 0
    end

    create index(:groups, :region)
  end
end

group.ex

# lib/test_app/groups/group.ex

defmodule TestApp.Groups.Group do
  use Ecto.Schema
  import Ecto.Changeset

  schema "groups" do
    field(:name, :string, null: false)
    field(:region, :string, null: false)
    field(:score, :integer, null: false)

    # Has to be virtual!
    field(:group_rank, :integer, virtual: true)
  end

  def changeset(group, attrs) do
    group
    |> cast(attrs, [:name, :region, :score])
    |> validate_required([:name, :region, :score])
  end
end