Migrating to a new ORM is not an easy process, and the transition cost can be prohibitive to many organizations. As much as we developers are enamoured by "Shiny New Things", the truth is that we rarely get a chance to work on a truly "green-field" project. Most of our careers, we operate in contexts where many technical and business constraints (a.k.a legacy systems) dictate and limit our options for moving forward. Developers of new technologies that want to succeed must offer interoperability capability and integration paths to help organizations seamlessly transition to a new way of solving an existing problem.
To help lower the cost of transitioning to Ent (or simply experimenting with it), we have started the "Schema Import Initiative" to help support many use cases for generating Ent schemas from external resources. The centrepiece of this effort is the schemast package (source code, docs) which enables developers to easily write programs that generate and manipulate Ent schemas. Using this package, developers can program in a high-level API, relieving them from worrying about code parsing and AST manipulations.
The first project to use this new API, is protoc-gen-ent, a protoc plugin to generate Ent schemas from .proto files (docs). Organizations that have existing schemas defined in Protobuf can use this tool to generate Ent code automatically. For example, taking a simple message definition:
Do you have schemas defined elsewhere that you would like to automatically import in to Ent? With the schemast package, it is easier than ever to write the tool that you need to do that. Not sure how to start? Want to collaborate with the community in planning and building out your idea? Reach out to our great community via our Discord server, Slack channel or start a discussion on GitHub!
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.
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:
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.
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:
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:
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:
Run go get -u entgo.io/contrib/entproto/cmd/protoc-gen-entgrpc to install protoc-gen-entgrpc
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" ) funcTestUserProto(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 Schemaโ
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:
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:
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" ) funcmain(){ // 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:
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" ) funcmain(){ 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) } funcrandomUser()*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!
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.
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.
Over the past few months, there has been much discussion in the Ent project issues about adding support for the retrieval of the foreign key field when retrieving entities with One-to-One or One-to-Many edges. We are happy to announce that as of v0.7.0 ent supports this feature.
Prior to merging this branch, a user that wanted to retrieve the foreign-key field for an entity needed to use eager-loading. Suppose our schema looked like this:
// ent/schema/user.go: // 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(). NotEmpty(), } } // Edges of the User. func(User)Edges()[]ent.Edge { return[]ent.Edge{ edge.From("pets", Pet.Type). Ref("owner"), } } // ent/schema/pet.go // 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"). NotEmpty(), } } // Edges of the Pet. func(Pet)Edges()[]ent.Edge { return[]ent.Edge{ edge.To("owner", User.Type). Unique(). Required(), } }
The schema describes two related entities: User and Pet, with a One-to-Many edge between them: a user can own many pets and a pet can have one owner.
When retrieving pets from the data storage, it is common for developers to want to access the foreign-key field on the pet. However, because this field is created implicitly from the owner edge it was automatically accessible when retrieving an entity. To retrieve this from the storage a developer needed to do something like:
funcTest(t *testing.T){ ctx := context.Background() c := enttest.Open(t, dialect.SQLite,"file:ent?mode=memory&cache=shared&_fk=1") defer c.Close() // Create the User u := c.User.Create(). SetUserName("rotem"). SaveX(ctx) // Create the Pet p := c.Pet. Create(). SetOwner(u).// Associate with the user SetName("donut"). SaveX(ctx) petWithOwnerId := c.Pet.Query(). Where(pet.ID(p.ID)). WithOwner(func(query *ent.UserQuery){ query.Select(user.FieldID) }). OnlyX(ctx) fmt.Println(petWithOwnerId.Edges.Owner.ID) // Output: 1 }
Aside from being very verbose, retrieving the pet with the owner this way was inefficient in-terms of database queries. If we execute the query with the .Debug() we can see the DB queries ent generates to satisfy this call:
Edge-field support greatly simplifies and improves the efficiency of this flow. With this feature, developers can define the foreign key field as part of the schemas Fields(), and by using the .Field(..) modifier on the edge definition instruct Ent to expose and map the foreign column to this field. So, in our example schema, we would modify it to be:
// user.go stays the same // pet.go // Fields of the Pet. func(Pet)Fields()[]ent.Field { return[]ent.Field{ field.String("name"). NotEmpty(), field.Int("owner_id"),// <-- explicitly add the field we want to contain the FK } } // Edges of the Pet. func(Pet)Edges()[]ent.Edge { return[]ent.Edge{ edge.To("owner", User.Type). Field("owner_id").// <-- tell ent which field holds the reference to the owner Unique(). Required(), } }
In order to update our client code we need to re-run code generation:
go generate ./...
We can now modify our query to be much simpler:
funcTest(t *testing.T){ ctx := context.Background() c := enttest.Open(t, dialect.SQLite,"file:ent?mode=memory&cache=shared&_fk=1") defer c.Close() u := c.User.Create(). SetUserName("rotem"). SaveX(ctx) p := c.Pet.Create(). SetOwner(u). SetName("donut"). SaveX(ctx) petWithOwnerId := c.Pet.GetX(ctx, p.ID)// <-- Simply retrieve the Pet fmt.Println(petWithOwnerId.OwnerID) // Output: 1 }
Running with the .Debug() modifier we can see that the DB queries make more sense now:
If you are already using Ent with an existing schema, you may already have O2M relations whose foreign-key columns already exist in your database. Depending on how you configured your schema, chances are that they may be stored in a column by a different name than the field you are now adding. For instance, you want to create an owner_id field, but Ent auto-created the column foreign-key column as pet_owner.
To check what column name Ent is using for this field you can look in the ./ent/migrate/schema.go file:
PetsColumns =[]*schema.Column{ {Name:"id", Type: field.TypeInt, Increment:true}, {Name:"name", Type: field.TypeString}, {Name:"pet_owner", Type: field.TypeInt, Nullable:true},// <-- this is our FK }
To allow for a smooth migration, you must explicitly tell Ent to keep using the existing column name. You can do this by using the StorageKey modifier (either on the field or on the edge). For example:
// In schema/pet.go: // Fields of the Pet. func(Pet)Fields()[]ent.Field { return[]ent.Field{ field.String("name"). NotEmpty(), field.Int("owner_id"). StorageKey("pet_owner"),// <-- explicitly set the column name } }
In the near future we plan to implement Schema Versioning, which will store the history of schema changes alongside the code. Having this information will allow ent to support such migrations in an automatic and predictable way.
The state of Go in Facebook Connectivity Tel Avivโ
20 months ago, I joined Facebook Connectivity (FBC) team in Tel Aviv after ~5 years of programming in Go and embedding it in a few companies.
I joined a team that was working on a new project and we needed to choose a language for this mission. We compared a few languages and decided to go with Go.
Since then, Go continued to spread across other FBC projects and became a big success with around 15 Go engineers in Tel Aviv alone. New services are now written in Go.
Most of my work in my 5 years before Facebook was on infra tooling and micro-services without too much data-model work. A service that was needed to do a little amount of work with an SQL database used one of the existing open-source solutions, but one that had worked with a complicated data model was written in a different language with a robust ORM. For example, Python with SQLAlchemy.
At Facebook we like to think about our data-model in graph concepts. We've had a good experience with this model internally.
The lack of a proper Graph-based ORM for Go, led us to write one here with the following principles:
Schema As Code - defining types, relations and constraints should be in Go code (not struct tags), and should be validated using a CLI tool. We have good experience with a similar tool internally at Facebook.
Statically typed and explicit API using codegen - API with interface{}s everywhere affects developers efficiency; especially project newbies.
Queries, aggregations and graph traversals should be simple - developers donโt want to deal with raw SQL queries nor SQL terms.
Predicates should be statically typed. No strings everywhere.
Full support for context.Context - This helps us to get full visibility in our traces and logs systems, and itโs important for other features like cancellation.
Storage agnostic - we tried to keep the storage layer dynamic using codegen templates, since the development initially started on Gremlin (AWS Neptune) and switched later to MySQL.
ent is an entity framework (ORM) for Go, built with the principles described above. ent makes it possible to define any data model or graph-structure in Go code easily; The schema configuration is verified by entc (the ent codegen) that generates an idiomatic and statically-typed API that keeps Go developers productive and happy. It supports MySQL, MariaDB, PostgreSQL, SQLite, and Gremlin-based graph databases.