Inheritance in Draft (Docs Update)

Draft supports schema inheritance, making it easier to reuse common fields across forms and domain models.A typical pattern is extracting shared fields like id and user_id into a base schema, then extending it across your app.

Base schema

defmodule Entity do
  use Draft.Schema

  schema do
    field :id,         :uuid
    field :user_id,    :uuid
    field :name,       :string
    field :role,       :string
  end
end

Extending for different forms

defmodule User do
  use Draft.Schema

  schema extends: Entity do
    field :email, :string
  end
end

defmodule Agent do
  use Draft.Schema

  schema extends: Entity do    
    field :active, :boolean
  end
end

Both User and Agent now share all base fields while defining their own.

Required fields propagate

defmodule Entity do
  use Draft.Schema

  schema required: true do
    field :id,      :uuid
    field :user_id, :uuid
  end
end

defmodule User do
  use Draft.Schema

  schema extends: Entity do
    field :email, :string, required: true
  end
end

User.new(email: "test@example.com")
# raises — :id and :user_id are required

Multi-level inheritance

defmodule Timestamps do
  use Draft.Schema

  schema do
    field :created_at, :datetime
    field :updated_at, :datetime
  end
end

defmodule Entity do
  use Draft.Schema

  schema extends: Timestamps do
    field :id, :uuid
    field :user_id, :uuid
  end
end

defmodule Agent do
  use Draft.Schema

  schema extends: Entity do
    field :role, :string
  end
end

Multiple inheritance

defmodule SoftDelete do
  use Draft.Schema

  schema do
    field :deleted_at, :datetime
  end
end

defmodule Agent do
  use Draft.Schema

  schema extends: [Entity, SoftDelete] do
    field :role, :string
  end
end

Overwriting inherited fields

defmodule User do
  use Draft.Schema

  schema extends: Entity do
    field :email, :string
  end
end

defmodule Agent do
  use Draft.Schema

  schema extends: User do
    field :email, :string, overwrite: true, format: :email
  end
end

Inheritance lets you define common form fields once and reuse them everywhere. While still allowing specialization, stricter validation, or composition when needed. This keeps your schemas consistent and eliminates duplication across forms, APIs, and internal models.

You might want to take a look at estructura, e. g. for the inspiration. It supports deeply nested structs, custom types with coercion and validation, andalso data generation for property-based testing.