JSON:API Resource Schema Generation: Anchor

Easily generate TypeScript schemas, JSON Schemas, or any schema of your choice from cerebris/jsonapi-resources JSONAPI::Resource classes.

Ideally, API schemas have the types of each payload fully specified.

To conveniently reach that ideal in a Ruby codebase that doesn't have static type signatures, Anchor automates type inference for attributes and relationships via the underlying ActiveRecord model of the JSONAPI::Resource.

If a type for an attribute or relationship can't be inferred or you'd like to specify it statically, you can annotate the attribute or relationship via types defined in Anchor::Types, see Annotations.

This gem provides TypeScript and JSON Schema generators with Anchor::TypeScript::SchemaGenerator and Anchor::JSONSchema::SchemaGenerator.

See the example Rails app for a fully functional example using Anchor. See example_schema_snapshot_spec.rb for Schema generation examples.

Inference

Attributes

JSONAPI::Resource attributes are inferred via introspection of the resource's underlying ActiveRecord model (JSONAPI::Resources._model_class).

ActiveRecord::Base.columns_hash[attribute] is used to get the SQL type and is then mapped to an Anchor::Type in Anchor::Types::Inference::ActiveRecord::SQL.from.

• Anchor.config.ar_column_to_type allows custom mappings, see
  spec/example/config/initializers/anchor.rb
• Anchor.config.use_active_record_presence can be set to true to infer
  nullable attributes (i.e. fields that do not specify null: false in
  schema.rb) as non-null when an unconditional
  validates :attribute_name, presence: true is present on the model

Relationships

JSONAPI::Resource relationships refer to other JSONAPI::Resource classes, so the JSONAPI::Resource.anchor_schema_name of the related relationship is used as a reference in the TypeScript and JSON Schema adapters.

Anchor infers whether the associated resource is nullable or an array via JSONAPI::Resource._model_class.reflections[name] where name is the first element of the JSONAPI::Resource._relationships [name, relationship] tuples.

• set Anchor.config.infer_nullable_relationships_as_optional to true to
  infer that the property associated with a nullable relationship will not be
  present if it's null
  • e.g. in TypeScript, setting the config to true will infer
    { relation?: Relation } over { relation: Maybe<Relation> }

Annotations

The APIs of JSONAPI::Resource.attribute and JSONAPI::Resource.relationship have been modified to take in an optional type parameter.

If the type can be inferred from the underlying ActiveRecord model the type argument isn't required.

If there is no type argument and the type cannot be inferred, then the type of the property will default to unknown.

The type argument has precedence over the inferred type.

For .attribute:

• after the name argument, specify any type from the table in
  Anchor::Types

For .relationship:

• after the name argument, specify a Anchor::Types::Relationship

The APIs of JSONAPI::Resource.attribute and JSONAPI::Resource.relationship remain the same if a type argument is not given.

If a type argument is given, the options for each will be the third argument.

Descriptions

If the description key is present in the options to .attribute or .relationship, it will be used in the provided TypeScript Schema generator as a comment for the property. The comment should show up in the LSP hover info.

With Anchor.config.use_active_record_presence = true, a default description will be inferred from the ActiveRecord column comment if it exists. Examples of both in spec/example/app/resources/exhaustive_resource.rb and its resulting TypeScript schema.

Generators

This gem provides generators for JSON Schema and TypeScript schemas via Schema.generate(adapter: :type_script | :json_schema).

Custom Generator

You can create your own generator by providing it to Schema.generate(adapter: MyGenerator).

It should inherit from Anchor::SchemaGenerator, e.g.

class MyGenerator < Anchor::SchemaGenerator
  def call
    raise NotImplementedError
  end
end

See Anchor::TypeScript::Resource, Anchor::TypeScript::Serializer, and Anchor::TypeScript::SchemaGenerator and the equivalents under Anchor::JSONSchema for examples.

Configuration

Guides

Create a schema serializable resource

class ApplicationResource
  include Anchor::SchemaSerializable
end

class SomeScope::UserResource < ApplicaionResource
  # optional schema_name definition
  # defaults to part of the string after the last :: (or class name itself if not nested) and removes Resource, in this case User
  schema_name "SpecialUser"

  attribute :name
  attribute :role, Anchor::Types::String

  relationship :profile, to: :one
  relationship :group, Anchor::Types::Relationship.new(resource: GroupResource, null: true), to: :one
end

Anchor::Schema

class Schema < Anchor::Schema
  resource CommentResource # register resources
  resource UserResource
  resource PostResource

  enum UserRoleEnum # register enums
end

Schema.generate will return the schema in a String.

Note: Currently, dependent resources and enums do not have their types generated. All resources and enums must be registered as part of the schema.

Anchor::Types

Note: The TypeScript type expression is derived from the Anchor::TypeScript::Serializer this gem provides for TypeScript schema generation. See Anchor::JSONSchema::Serializer for the given JSON Schema generator.

module Anchor::Types
  # @!attribute [r] resource
  #   @return [JSONAPI::Resource, NilClass] the associated resource
  # @!attribute [r] resources
  #   @return [Array<JSONAPI::Resource>, NilClass] union of associated resources
  # @!attribute [r] null
  #   @return [Boolean] whether the relationship can be `null`
  # @!attribute [r] null_elements
  #   @return [Boolean] whether the elements in a _many_ relationship can be `null`
  Relationship = Struct.new(:resource, :resources, :null, :null_elements, keyword_init: true)
end

Anchor::Types::Object

class CustomPayload < Anchor::Types::Object
  property :id, Anchor::Types::String, optional: true, description: "ID of payload."
end

Anchor::Types::Enum

class UserRoleEnum < Anchor::Types::Enum
  schema_name "UserRole" # optional, similar logic to Resource but removes Enum

  # First argument is the enum member identifier that gets camelized
  # Second argument is the value
  value :admin, "admin"
  value :content_creator, "content_creator"
  value :external, "external"
  value :guest, "guest"
  value :system, "system"
end

# alternatively
class User < ApplicationRecord
  enum :role, {
    admin: "admin",
    conent_creator: "content_creator",
    external: "external",
    guest: "guest",
    system: "system",
  }
end

class UserRoleEnum < Anchor::Types::Enum
  User.roles.each { |key, val| value key, val }
end

Very similar to rmosolgo/graphql-ruby enums.

Example

Given:

ActiveRecord Schema:

  create_table "comments", force: :cascade do |t|
    t.string "text", null: false
    t.string "commentable_type"
    t.bigint "commentable_id"
    t.bigint "user_id", null: false
    t.bigint "deleted_by_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["commentable_type", "commentable_id"], name: "index_comments_on_commentable"
    t.index ["deleted_by_id"], name: "index_comments_on_deleted_by_id"
    t.index ["user_id"], name: "index_comments_on_user_id"
  end

  create_table "posts", force: :cascade do |t|
    t.string "description", null: false
    t.bigint "user_id", null: false
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["user_id"], name: "index_posts_on_user_id"
  end

  create_table "users", force: :cascade do |t|
    t.string "name", null: false
    t.integer "integer"
    t.decimal "decimal"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "role"
  end

JSONAPI::Resource classes:

class ApplicaionResource
  include Anchor::SchemaSerializable
end

class CommentResource < ApplicationResource
  attribute :text
  attribute :created_at
  attribute :updated_at
  attribute :inferred_unknown
  attribute :type_given, Anchor::Types::String

  relationship :user, to: :one
  relationship :commentable, Anchor::Types::Relationship.new(resources: [UserResource, PostResource], null: true), polymorphic: true, to: :one
end

class UserResource < ApplicationResource
  attribute :name
  attribute :role, UserRoleEnum

  relationship :comments, to: :many
  relationship :posts, to: :many
end

class UserRoleEnum < Anchor::Types::Enum
  schema_name "UserRole"

  value :admin, "admin"
  value :content_creator, "content_creator"
  value :external, "external"
  value :guest, "guest"
  value :system, "system"
end

class PostResource < ApplicationResource
  attribute :description

  relationship :user, to: :one
  relationship :comment, to: :many
end

class Schema < Anchor::Schema
  resource CommentResource
  resource UserResource
  resource PostResource

  enum UserRoleEnum
end

Schema.generate(adapter: :type_script) will return the schema below in a String:

type Maybe<T> = T | null;

export type Comment = {
  id: number;
  type: "comments";
  text: string;
  created_at: string;
  updated_at: string;
  inferred_unknown: unknown;
  type_given: string;
  relationships: {
    user: User;
    commentable: Maybe<User | Post>;
  };
};

export type User = {
  id: number;
  type: "users";
  name: string;
  role: UserRole;
  relationships: {
    comments: Array<Comment>;
    posts: Array<Post>;
  };
};

export type Post = {
  id: number;
  type: "posts";
  description: string;
  relationships: {
    user: User;
    comment: Array<Comment>;
  };
};

export enum UserRole {
  Admin = "admin",
  ContentCreator = "content_creator",
  External = "external",
  Guest = "guest",
  System = "system",
}

References

• @nopelluhh
• ElMassimo/types_from_serializers
• rmosolgo/graphql-ruby

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