Absinthe - Schema Design

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

• Organize types by domain - Group related types in separate modules

• Use non_null sparingly - Only for truly required fields

• Leverage interfaces - For shared fields across types

• Define input objects - For complex mutation arguments

• 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