go get -u /vektah/gqlgen

type Todo {
id: ID!
text: String!
done: Boolean!
user: User!
}

type User {
id: ID!
name: String!
}

type Query {
todos: [Todo!]!
}

input NewTodo {
text: String!
userId: String!
}

type Mutation {
createTodo(input: NewTodo!): Todo!
}

package model

// User user info
type User struct {
    ID string
    Name string
}

package model

// Todo todo ino
type Todo struct {
    ID string
    Text string
    Done bool
    UserID string
}

schema: schema.graphql
exec:
  filename: graph/generated.go
model:
  filename: model/generated.go

models:
  Todo:
    model: /rongfengliang/gqlgen-app/model.Todo
  User:
    model: /rongfengliang/gqlgen-app/model.User

gqlgen

package graph

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

    model "/rongfengliang/gqlgen-app/model"
)

type App struct {
    todos []model.Todo
}

func (a *App) Mutation() MutationResolver {
    return &mutationResolver{a}
}

func (a *App) Query() QueryResolver {
    return &queryResolver{a}
}

func (a *App) Todo() TodoResolver {
    return &todoResolver{a}
}

type queryResolver struct{ *App }

func (a *queryResolver) Todos(ctx context.Context) ([]model.Todo, error) {
    return a.todos, nil
}

type mutationResolver struct{ *App }

func (a *mutationResolver) CreateTodo(ctx context.Context, input model.NewTodo) (model.Todo, error) {
    todo := model.Todo{
        Text: input.Text,
        ID: fmt.Sprintf("T%d", rand.Int()),
        UserID: input.UserId,
    }
    a.todos = append(a.todos, todo)
    return todo, nil
}

type todoResolver struct{ *App }

func (a *todoResolver) User(ctx context.Context, it *model.Todo) (model.User, error) {
    return model.User{ID: it.UserID, Name: "user " + it.UserID}, nil
}

package main

import (
    "fmt"
    "log"
    "net/http"

    "/rongfengliang/gqlgen-app/graph"
    "/vektah/gqlgen/handler"
)

func main() {
    http.Handle("/", handler.Playground("Todo", "/query"))
    http.Handle("/query", handler.GraphQL(graph.NewExecutableSchema(&graph.App{})))

    fmt.Println("Listening on :8080")
    log.Fatal(http.ListenAndServe(":8080", nil))
}

go run main.go

dep init