Skip to main content

Generate a fully-working Go gRPC server in two minutes with Ent

· 11 min read
Rotem Tamir

ent + gRPC

Introduction​

Having entity schemas defined in a central, language-neutral format has many benefits as the scale of software engineering organizations increase. To do this, many organizations use Protocol Buffers as their interface definition language (IDL). In addition, gRPC, a Protobuf-based RPC framework modeled after Google's internal Stubby is becoming increasingly popular due to its efficiency and code-generation capabilities.

Being an IDL, gRPC does not prescribe any specific guidelines on implementing the data access layer so implementations vary greatly. Ent is a natural candidate for building the data access layer in any Go application and so there is great potential in integrating the two technologies together.

Today we announce an experimental version of entproto, a Go package, and a command-line tool to add Protobuf and gRPC support for ent users. With entproto, developers can set up a fully working CRUD gRPC server in a few minutes. In this post, we will show exactly how to do just that.

Setting Up​

The final version of this tutorial is available on GitHub, you can clone it if you prefer following along that way.

Let's start by initializing a new Go module for our project:

mkdir ent-grpc-example
cd ent-grpc-example
go mod init ent-grpc-example

Next we use go run to invoke the ent code generator to initialize a schema:

go run -mod=mod entgo.io/ent/cmd/ent new User

Our directory should now look like:

.
├── ent
│   ├── generate.go
│   └── schema
│       └── user.go
├── go.mod
└── go.sum

Next, let's add the entproto package to our project:

go get -u entgo.io/contrib/entproto

Next, we will define the schema for the User entity. Open ent/schema/user.go and edit:

package schema

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

// 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").
            Unique(),
        field.String("email_address").
            Unique(),
    }
}

In this step, we added two unique fields to our User entity: name and email_address. The ent.Schema is just the definition of the schema, to create usable production code from it we need to run Ent's code generation tool on it. Run:

go generate ./...

Notice the a bunch of new files were created from our schema definition now:

├── ent
│   ├── client.go
│   ├── config.go
// .... many more
│   ├── user
│   ├── user.go
│   ├── user_create.go
│   ├── user_delete.go
│   ├── user_query.go
│   └── user_update.go
├── go.mod
└── go.sum

At this point, we can open a connection to a database, run a migration to create the users table, and start reading and writing data to it. This is covered on the Setup Tutorial, so let's cut to the chase and learn about generating Protobuf definitions and gRPC servers from our schema.

Generating Go Protobufs with entproto​

As ent and Protobuf schemas are not identical, we must supply some annotations on our schema to help entproto figure out exactly how to generate Protobuf definitions (called "Messages" in protobuf lingo).

The first thing we need to do is to add an entproto.Message() annotation. This is our opt-in to Protobuf schema generation, we don't necessarily want to generate proto messages or gRPC service definitions from all of our schema entities, and this annotation gives us that control. To add it, append to ent/schema/user.go:

func (User) Annotations() []schema.Annotation {
    return []schema.Annotation{
        entproto.Message(),
    }
}

Next, we need to annotate each field and assign it a field number. Recall that when defining a protobuf message type, each field must be assigned a unique number. To do that, we add an entproto.Field annotation on each field. Update the Fields in ent/schema/user.go:

// Fields of the User.
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.String("name").
            Unique().
            Annotations(
                entproto.Field(2),
            ),
        field.String("email_address").
            Unique().
            Annotations(
                entproto.Field(3),
            ),
    }
}

Notice that we did not start our field numbers from 1, this is because ent implicitly creates the ID field for the entity, and that field is automatically assigned the number 1. We can now generate our protobuf message type definitions. To do that, we will add to ent/generate.go a go:generate directive that invokes the entproto command-line tool. It should now look like this:

package ent

//go:generate go run -mod=mod entgo.io/ent/cmd/ent generate ./schema
//go:generate go run -mod=mod entgo.io/contrib/entproto/cmd/entproto -path ./schema

Let's re-generate our code:

go generate ./...

Observe that a new directory was created which will contain all protobuf related generated code: ent/proto. It now contains:

ent/proto
└── entpb
    ├── entpb.proto
    └── generate.go

Two files were created. Let's look at their contents:

// Code generated by entproto. DO NOT EDIT.
syntax = "proto3";

package entpb;

option go_package = "ent-grpc-example/ent/proto/entpb";

message User {
  int32 id = 1;

  string user_name = 2;

  string email_address = 3;
}

Nice! A new .proto file containing a message type definition that maps to our User schema was created!

package entpb
//go:generate protoc -I=.. --go_out=.. --go-grpc_out=.. --go_opt=paths=source_relative --go-grpc_opt=paths=source_relative --entgrpc_out=.. --entgrpc_opt=paths=source_relative,schema_path=../../schema entpb/entpb.proto

A new generate.go file was created with an invocation to protoc, the protobuf code generator instructing it how to generate Go code from our .proto file. For this command to work, we must first install protoc as well as 3 protobuf plugins: protoc-gen-go (which generates Go Protobuf structs), protoc-gen-go-grpc (which generates Go gRPC service interfaces and clients), and protoc-gen-entgrpc (which generates an implementation of the service interface). If you do not have these installed, please follow these directions:

After installing these dependencies, we can re-run code-generation:

go generate ./...

Observe that a new file named ent/proto/entpb/entpb.pb.go was created which contains the generated Go structs for our entities.

Let's write a test that uses it to make sure everything is wired correctly. Create a new file named pb_test.go and write:

package main

import (
    "testing"

    "ent-grpc-example/ent/proto/entpb"
)

func TestUserProto(t *testing.T) {
    user := entpb.User{
        Name:     "rotemtam",
        EmailAddress: "rotemtam@example.com",
    }
    if user.GetName() != "rotemtam" {
        t.Fatal("expected user name to be rotemtam")
    }
    if user.GetEmailAddress() != "rotemtam@example.com" {
        t.Fatal("expected email address to be rotemtam@example.com")
    }
}

To run it:

go get -u./... # install deps of the generated package
go test ./...

Hooray! The test passes. We have successfully generated working Go Protobuf structs from our Ent schema. Next, let's see how to automatically generate a working CRUD gRPC server from our schema.

Generating a Fully Working gRPC Server from our Schema​

Having Protobuf structs generated from our ent.Schema can be useful, but what we're really interested in is getting an actual server that can create, read, update, and delete entities from an actual database. To do that, we need to update just one line of code! When we annotate a schema with entproto.Service, we tell the entproto code-gen that we are interested in generating a gRPC service definition, from the protoc-gen-entgrpc will read our definition and generate a service implementation. Edit ent/schema/user.go and modify the schema's Annotations:

func (User) Annotations() []schema.Annotation {
    return []schema.Annotation{
        entproto.Message(),
+       entproto.Service(), // <-- add this
    }
}

Now re-run code-generation:

go generate ./...

Observe some interesting changes in ent/proto/entpb:

ent/proto/entpb
├── entpb.pb.go
├── entpb.proto
├── entpb_grpc.pb.go
├── entpb_user_service.go
└── generate.go

First, entproto added a service definition to entpb.proto:

service UserService {
  rpc Create ( CreateUserRequest ) returns ( User );

  rpc Get ( GetUserRequest ) returns ( User );

  rpc Update ( UpdateUserRequest ) returns ( User );

  rpc Delete ( DeleteUserRequest ) returns ( google.protobuf.Empty );
}

In addition, two new files were created. The first, ent_grpc.pb.go, contains the gRPC client stub and the interface definition. If you open the file, you will find in it (among many other things):

// UserServiceClient is the client API for UserService service.
//
// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://pkg.go.dev/google.golang.org/grpc/?tab=doc#ClientConn.NewStream.
type UserServiceClient interface {
    Create(ctx context.Context, in *CreateUserRequest, opts ...grpc.CallOption) (*User, error)
    Get(ctx context.Context, in *GetUserRequest, opts ...grpc.CallOption) (*User, error)
    Update(ctx context.Context, in *UpdateUserRequest, opts ...grpc.CallOption) (*User, error)
    Delete(ctx context.Context, in *DeleteUserRequest, opts ...grpc.CallOption) (*emptypb.Empty, error)
}

The second file, entpub_user_service.go contains a generated implementation for this interface. For example, an implementation for the Get method:

// Get implements UserServiceServer.Get
func (svc *UserService) Get(ctx context.Context, req *GetUserRequest) (*User, error) {
    get, err := svc.client.User.Get(ctx, int(req.GetId()))
    switch {
    case err == nil:
        return toProtoUser(get), nil
    case ent.IsNotFound(err):
        return nil, status.Errorf(codes.NotFound, "not found: %s", err)
    default:
        return nil, status.Errorf(codes.Internal, "internal error: %s", err)
    }
}

Not bad! Next, let's create a gRPC server that can serve requests to our service.

Creating the Server​

Create a new file cmd/server/main.go and write:

package main

import (
    "context"
    "log"
    "net"

    _ "github.com/mattn/go-sqlite3"
    "ent-grpc-example/ent"
    "ent-grpc-example/ent/proto/entpb"
    "google.golang.org/grpc"
)

func main() {
    // Initialize an ent client.
    client, err := ent.Open("sqlite3", "file:ent?mode=memory&cache=shared&_fk=1")
    if err != nil {
        log.Fatalf("failed opening connection to sqlite: %v", err)
    }
    defer client.Close()

    // Run the migration tool (creating tables, etc).
    if err := client.Schema.Create(context.Background()); err != nil {
        log.Fatalf("failed creating schema resources: %v", err)
    }

    // Initialize the generated User service.
    svc := entpb.NewUserService(client)

    // Create a new gRPC server (you can wire multiple services to a single server).
    server := grpc.NewServer()

    // Register the User service with the server.
    entpb.RegisterUserServiceServer(server, svc)

    // Open port 5000 for listening to traffic.
    lis, err := net.Listen("tcp", ":5000")
    if err != nil {
        log.Fatalf("failed listening: %s", err)
    }

    // Listen for traffic indefinitely.
    if err := server.Serve(lis); err != nil {
        log.Fatalf("server ended: %s", err)
    }
}

Notice that we added an import of github.com/mattn/go-sqlite3, so we need to add it to our module:

go get -u github.com/mattn/go-sqlite3

Next, let's run the server, while we write a client that will communicate with it:

go run -mod=mod ./cmd/server

Creating the Client​

Let's create a simple client that will make some calls to our server. Create a new file named cmd/client/main.go and write:

package main

import (
    "context"
    "fmt"
    "log"
    "math/rand"
    "time"

    "ent-grpc-example/ent/proto/entpb"
    "google.golang.org/grpc"
    "google.golang.org/grpc/status"
)

func main() {
    rand.Seed(time.Now().UnixNano())

    // Open a connection to the server.
    conn, err := grpc.Dial(":5000", grpc.WithInsecure())
    if err != nil {
        log.Fatalf("failed connecting to server: %s", err)
    }
    defer conn.Close()

    // Create a User service Client on the connection.
    client := entpb.NewUserServiceClient(conn)

    // Ask the server to create a random User.
    ctx := context.Background()
    user := randomUser()
    created, err := client.Create(ctx, &entpb.CreateUserRequest{
        User: user,
    })
    if err != nil {
        se, _ := status.FromError(err)
        log.Fatalf("failed creating user: status=%s message=%s", se.Code(), se.Message())
    }
    log.Printf("user created with id: %d", created.Id)

    // On a separate RPC invocation, retrieve the user we saved previously.
    get, err := client.Get(ctx, &entpb.GetUserRequest{
        Id: created.Id,
    })
    if err != nil {
        se, _ := status.FromError(err)
        log.Fatalf("failed retrieving user: status=%s message=%s", se.Code(), se.Message())
    }
    log.Printf("retrieved user with id=%d: %v", get.Id, get)
}

func randomUser() *entpb.User {
    return &entpb.User{
        Name:         fmt.Sprintf("user_%d", rand.Int()),
        EmailAddress: fmt.Sprintf("user_%d@example.com", rand.Int()),
    }
}

Our client creates a connection to port 5000, where our server is listening, then issues a Create request to create a new user, and then issues a second Get request to retrieve it from the database. Let's run our client code:

go run ./cmd/client

Observe the output:

2021/03/18 10:42:58 user created with id: 1
2021/03/18 10:42:58 retrieved user with id=1: id:1 name:"user_730811260095307266" email_address:"user_7338662242574055998@example.com"

Amazing! With a few annotations on our schema, we used the super-powers of code generation to create a working gRPC server in no time!

Caveats and Limitations​

entproto is still experimental stage and lacks some basic functionality. For example, many applications will probably want a List or Find method on their service, but these are not yet supported. In addition, some other issues we plan to tackle in the near future:

  • Currently only "unique" edges are supported (O2O, O2M).
  • The generated "mutating" methods (Create/Update) currently set all fields, disregarding zero/null values and field nullability.
  • All fields are copied from the gRPC request to the ent client, support for configuring some fields to be unsettable via the service by adding a field/edge annotation is also planned.

Next Steps​

We believe that ent + gRPC can be a great way to build server applications in Go. For example, to set granular access control to the entities managed by our application, developers can already use Privacy Policies that work out-of-the-box with the gRPC integration. To run any arbitrary Go code on the different lifecycle events of entities, developers can utilize custom Hooks.

Do you want to build gRPC servers with ent? If you want some help setting up or want the integration to support your use case, please reach out to us via our Discussions Page on GitHub or in the #ent channel on the Gophers Slack or our Discord server.

For more Ent news and updates: