Overview

Comprehensive guide to designing GraphQL schemas with Absinthe in Elixir.

Key Concepts

Type Definitions

defmodule MyApp.Schema.Types do
  use Absinthe.Schema.Notation

  object :user do
    field :id, non_null(:id)
    field :name, non_null(:string)
    field :email, :string
    field :posts, list_of(:post) do
      resolve &MyApp.Resolvers.User.posts/3
    end
    field :inserted_at, :datetime
  end

  object :post do
    field :id, non_null(:id)
    field :title, non_null(:string)
    field :body, :string
    field :author, :user do
      resolve &MyApp.Resolvers.Post.author/3
    end
  end
end

Interfaces

interface :node do
  field :id, non_null(:id)

  resolve_type fn
    %MyApp.User{}, _ -> :user
    %MyApp.Post{}, _ -> :post
    _, _ -> nil
  end
end

object :user do
  interface :node
  field :id, non_null(:id)
  field :name, non_null(:string)
end

Unions

union :search_result do
  types [:user, :post, :comment]

  resolve_type fn
    %MyApp.User{}, _ -> :user
    %MyApp.Post{}, _ -> :post
    %MyApp.Comment{}, _ -> :comment
    _, _ -> nil
  end
end

Enums

enum :post_status do
  value :draft, as: "draft"
  value :published, as: "published"
  value :archived, as: "archived"
end

Input Objects

input_object :create_post_input do
  field :title, non_null(:string)
  field :body, :string
  field :status, :post_status, default_value: :draft
end

Best Practices

1. Organize types by domain - Group related types in separate modules
2. Use non_null sparingly - Only for truly required fields
3. Leverage interfaces - For shared fields across types
4. Define input objects - For complex mutation arguments
5. Use custom scalars - For dates, UUIDs, JSON, etc.

Schema Organization

defmodule MyApp.Schema do
  use Absinthe.Schema

  import_types MyApp.Schema.Types
  import_types MyApp.Schema.Queries
  import_types MyApp.Schema.Mutations
  import_types MyApp.Schema.Subscriptions
  import_types Absinthe.Type.Custom  # DateTime, etc.

  query do
    import_fields :user_queries
    import_fields :post_queries
  end

  mutation do
    import_fields :user_mutations
    import_fields :post_mutations
  end

  subscription do
    import_fields :post_subscriptions
  end
end

Custom Scalars

scalar :uuid, name: "UUID" do
  serialize &to_string/1
  parse &parse_uuid/1
end

defp parse_uuid(%Absinthe.Blueprint.Input.String{value: value}) do
  case Ecto.UUID.cast(value) do
    {:ok, uuid} -> {:ok, uuid}
    :error -> :error
  end
end

defp parse_uuid(_), do: :error

Anti-Patterns

• Avoid deeply nested types without pagination
• Don't expose database IDs directly without consideration
• Avoid circular dependencies in type definitions
• Don't skip field descriptions for documentation