elk

This package aims to extend the awesome entgo.io code generator to generate a fully-functional HTTP API for your schema. elk strives to automate all the tedious work of setting up the basic CRUD endpoints for every entity you add to your graph, including logging, validation of the request body, eager loading relations and serializing, all while leaving reflection out of sight and maintaining type-safety.

⚠️ This is work in progress: The API may change without further notice!

This package depends on Ent, an ORM project for Go. To learn more about Ent, how to connect to different types of databases, run migrations or work with entities head over to their documentation.

Getting Started

The first step is to add the elk package to your project:

go get github.com/masseelch/elk

elk uses the Ent extension API to integrate with Ent’s code-generation. This requires that we use the entc (ent codegen) package as described here. Follow the next four steps to enable it and to configure Ent to work with the elk extension:

Create a new Go file named ent/entc.go and paste the following content:

// +build ignore

package main

import (
	"log"

	"entgo.io/ent/entc"
	"entgo.io/ent/entc/gen"
	"github.com/masseelch/elk"
)

func main() {
	ex, err := elk.NewExtension()
	if err != nil {
		log.Fatalf("creating elk extension: %v", err)
	}
	err = entc.Generate("./schema", &gen.Config{}, entc.Extensions(ex))
	if err != nil {
		log.Fatalf("running ent codegen: %v", err)
	}
}

Edit the ent/generate.go file to execute the ent/entc.go file:

package ent

//go:generate go run -mod=mod entc.go

elk uses some external packages in its generated code. Currently, you have to get those packages manually once when setting up elk:

go get github.com/mailru/easyjson github.com/masseelch/render github.com/go-chi/chi/v5 go.uber.org/zap

Run the code generator:

go generate ./...

In addition to the files Ent would normally generate, another directory names ent/http was created. There files contain the code for the elk-generated HTTP CRUD handlers. An example of the generated code can be found here.

Setting up a server

This section guides you to a very simple setup for an elk-powered Ent. The following two files define two schemas Pet and User with a Many-To-One relation: A Pet belongs to a User, and a User can have multiple Pets.

ent/schema/pet.go

package schema

import (
	"entgo.io/ent"
	"entgo.io/ent/schema/edge"
	"entgo.io/ent/schema/field"
)

// Pet holds the schema definition for the Pet entity.
type Pet struct {
	ent.Schema
}

// Fields of the Pet.
func (Pet) Fields() []ent.Field {
	return []ent.Field{
		field.String("name"),
	}
}

// Edges of the Pet.
func (Pet) Edges() []ent.Edge {
	return []ent.Edge{
		edge.From("owner", User.Type).
			Ref("pets").
			Unique(),
	}
}

ent/schema/user.go

package schema

import (
	"entgo.io/ent"
	"entgo.io/ent/schema/edge"
	"entgo.io/ent/schema/field"
)

// User holds the schema definition for the User entity.
type User struct {
	ent.Schema
}

// Fields of the User.
func (User) Fields() []ent.Field {
	return []ent.Field{
		field.String("name"),
	}
}

// Edges of the User.
func (User) Edges() []ent.Edge {
	return []ent.Edge{
		edge.To("pets", Pet.Type),
	}
}

To spin up a runnable server you can use the below main function:

package main

import (
	"context"
	"log"
	"net/http"

	"<your-project>/ent"
	elk "<your-project>/ent/http"

	"github.com/go-chi/chi/v5"
	_ "github.com/mattn/go-sqlite3"
	"go.uber.org/zap"
)

func main() {
	// Create the ent client. This opens up a sqlite file named elk.db.
	c, err := ent.Open("sqlite3", "./elk.db?_fk=1")
	if err != nil {
		log.Fatalf("failed opening connection to sqlite: %v", err)
	}
	defer c.Close()
	// Run the auto migration tool.
	if err := c.Schema.Create(context.Background()); err != nil {
		log.Fatalf("failed creating schema resources: %v", err)
	}
	// Router and Logger.
	r, l := chi.NewRouter(), zap.NewExample()
	// Mount the generates handlers.
	r.Route("/pets", func(r chi.Router) {
		elk.NewPetHandler(c, l).Mount(r, elk.PetRoutes)
	})
	r.Route("/users", func(r chi.Router) {
		// Only register the create and read endpoints.
		elk.NewUserHandler(c, l).Mount(r, elk.UserCreate|elk.UserRead)
	})
	// Start listen to incoming requests.
	if err := http.ListenAndServe(":8080", r); err != nil {
		log.Fatal(err)
	}
}

Start the server:

go run -mod=mod main.go

Congratulations! You now have a running server serving the Pets API. The database is still empty though. the following two curl requests create a new user and adds a pet, that belongs to that user.

curl -X 'POST' -H 'Content-Type: application/json' -d '{"name":"Elk"}' 'localhost:8080/users'

{
  "id": 1,
  "name": "Elk"
}

curl -X 'POST' -H 'Content-Type: application/json' -d '{"name":"Kuro","owner":1}' 'localhost:8080/pets'

{
  "id": 1,
  "name": "Kuro"
}

The response data on the create action does not include the User the new Pet belongs to. elk does not include edges in its output by default. You can configure elk to render edges using a feature called serialization groups.

Serialization Groups

elk by default includes every field of a schema in an endpoints output and excludes fields. This behaviour can be changed by using serialization groups. You can configure elk what serialization groups to request on what endpoint using a elk.SchemaAnnotation. With a elk.Annotation you configure what fields and edges to include. elk follows the following rules to determine if a field or edge is inlcuded or not:

If no groups are requested all fields are included and all edges are excluded
If a group x is requested all fields with no groups and fields with group x are included. Edges with x are eager loaded and rendered.

Change the previously mentioned schemas and add serialization groups:

ent/schema/pet.go

package schema

import (
	"entgo.io/ent"
	"entgo.io/ent/schema"
	"entgo.io/ent/schema/edge"
	"entgo.io/ent/schema/field"
	"github.com/masseelch/elk"
)

// Pet holds the schema definition for the Pet entity.
type Pet struct {
	ent.Schema
}

// Fields of the Pet.
func (Pet) Fields() []ent.Field {
	return []ent.Field{
		field.String("name"),
	}
}

// Edges of the Pet.
func (Pet) Edges() []ent.Edge {
	return []ent.Edge{
		edge.From("owner", User.Type).
			Ref("pets").
			Unique().
			// render this edge if one of 'pet:read' or 'pet:list' is requested.
			Annotations(elk.Groups("pet:read", "pet:list")),
	}
}

// Annotations of the Pet.
func (Pet) Annotations() []schema.Annotation {
	return []schema.Annotation{
		// Request the 'pet:read' group when rendering the entity after creation.
		elk.CreateGroups("pet:read"),
		// You can request several groups per endpoint.
		elk.ReadGroups("pet:list", "pet:read"),
	}
}

ent/schema/user.go

package schema

import (
	"entgo.io/ent"
	"entgo.io/ent/schema/edge"
	"entgo.io/ent/schema/field"
	"github.com/masseelch/elk"
)

// User holds the schema definition for the User entity.
type User struct {
	ent.Schema
}

// Fields of the User.
func (User) Fields() []ent.Field {
	return []ent.Field{
		field.String("name").
			// render this field only if no groups or the 'owner:read' groups is requested.
			Annotations(elk.Groups("owner:read")),
	}
}

// Edges of the User.
func (User) Edges() []ent.Edge {
	return []ent.Edge{
		edge.To("pets", Pet.Type),
	}
}

After regenerating the code and restarting the server elk renders the owner if you create a new pet.

curl -X 'POST' -H 'Content-Type: application/json' -d '{"name":"Martha","owner":1}' 'localhost:8080/pets'

{
  "id": 2,
  "name": "Martha",
  "owner": {
    "id": 1,
    "name": "Elk"
  }
}

Validation

elk supports the validation feature of Ent. For demonstration extend the above Pet schema:

package schema

import (
	"errors"
	"strings"

	"entgo.io/ent"
	"entgo.io/ent/schema"
	"entgo.io/ent/schema/edge"
	"entgo.io/ent/schema/field"
	"github.com/masseelch/elk"
)

// Pet holds the schema definition for the Pet entity.
type Pet struct {
	ent.Schema
}

// Fields of the Pet.
func (Pet) Fields() []ent.Field {
	return []ent.Field{
		field.Int("age").
			// Validator will only be called if the request body has a 
			// non nil value for the field 'age'.
			Optional().
			// Works for built-in validators.
			Positive(),
		field.String("name").
			// Works for built-in validators.
			MinLen(3).
			// Works for custom validators.
			Validate(func(s string) error {
				if strings.ToLower(s) == s {
					return errors.New("name must begin with uppercase")
				}
				return nil
			}),
		// Enums are validated against the allowed values.
		field.Enum("color").
			Values("red", "blue", "green", "yellow"),
	}
}

// Edges of the Pet.
func (Pet) Edges() []ent.Edge {
	return []ent.Edge{
		edge.From("owner", User.Type).
			Ref("pets").
			Unique().
			// Works with edge validation.
			Required().
			// render this edge if one of 'pet:read' or 'pet:list' is requested.
			Annotations(elk.Groups("pet:read", "pet:list")),
	}
}

// Annotations of the Pet.
func (Pet) Annotations() []schema.Annotation {
	return []schema.Annotation{
		// Request the 'pet:read' group when rendering the entity after creation.
		elk.CreateGroups("pet:read"),
		// You can request several groups per endpoint.
		elk.ReadGroups("pet:list", "pet:read"),
	}
}

Sub Resources

elk provides first level sub resource handlers for all your entities. With previously set up server, run the following:

curl 'localhost:8080/pets/1/owner'

You'll get information about the Owner of the Pet with the id 1. elk uses elk.SchemaAnnotation.ReadGroups for a unique edge and elk.SchemaAnnotation.ListGroups for a non-unique edge.

Pagination

elk paginates list endpoints. This is valid for both resource and sub-resources routes.

curl 'localhost:8080/pets?page=2&itemsPerPage=1'

[
  {
    "id": 2,
    "name": "Martha"
  }
]

For more information about how to configure elk and what it can do have a look at the integration test setup.

Known Issues and Outlook

elk does currently only work with JSON. It is relatively easy to support XML as well and there are plans to provide conditional XML / JSON parsing and rendering based on the Content-Type and Accept headers.
elks generated bitmask to choose what handlers to mount is not typesafe yet. You can call elk.FooHandler(c, l).Mount(r, elk.BarRoutes) without any compile time errors.
Customization of the generated handlers is not great yet. I'd like to provide something similar to Ent' s External Templates in the future.
The generated code does not have very good automated tests yet.
Initial work to generate a fully working flutter frontend has been done.

Contribution

elk is in an early stage of development, we welcome any suggestion or feedback and if you are willing to help I'd be very glad. The issues tab is a wonderful place for you to reach out for help, feedback, suggestions and contribution.

quynguyenxuan / elk

elk