使用gqlgen搭建graphql的go服务端

添加依赖

require (
	github.com/99designs/gqlgen v0.11.3
	github.com/vektah/gqlparser/v2 v2.0.1
)

编写schema

在项目根目录创建文件夹，graph，在graph文件夹中新建schema.graphqls文件，在其中编写schema定义，比如

type Query {
    hello: String
}

生成go代码

在项目根目录新建go源代码，内容为

package main

import "github.com/99designs/gqlgen/cmd"

func main() {
	cmd.Execute()
}

接下来，使用命令生成相关go代码

go run 源代码文件名.go init

此时命令行会输出

validation failed: packages.Load: -: package test/graph/model is not in GOROOT ...

这是因为我们没有在graph文件夹中，创建graph的modal文件夹及源文件（因为我们没有定义其他type，不需要用到，不影响）
此时执行后，目录结构为

Mode                LastWriteTime         Length Name
----                -------------         ------ ----
d-----         2020/5/5     16:08                graph
-a----         2020/5/4     17:44            110 go.mod
-a----         2020/5/4     17:44           7599 go.sum
-a----         2020/5/4     17:15             94 gqlgen.go
-a----         2020/5/5     16:08           1667 gqlgen.yml
-a----         2020/5/5     16:08            635 server.go

其中的gqlgen.yml和server.go是自动生成的代码，server.go就是运行这个graph服务端程序的go代码，默认使用8080端口，直接将其作为普通go程序运行则代表启动服务端，这里还不能启动，因为我们定义的schema里的查询还没有编写实现

package main

import (
	"log"
	"net/http"
	"os"
	"test/graph"
	"test/graph/generated"

	"github.com/99designs/gqlgen/graphql/handler"
	"github.com/99designs/gqlgen/graphql/playground"
)

const defaultPort = "8080"

func main() {
	port := os.Getenv("PORT")
	if port == "" {
		port = defaultPort
	}

	srv := handler.NewDefaultServer(generated.NewExecutableSchema(generated.Config{Resolvers: &graph.Resolver{}}))

	http.Handle("/", playground.Handler("GraphQL playground", "/query"))
	http.Handle("/query", srv)

	log.Printf("connect to http://localhost:%s/ for GraphQL playground", port)
	log.Fatal(http.ListenAndServe(":"+port, nil))
}

gqlgen.yml是默认的配置文件，配置了如何读取graph文件夹下内容进行go代码生成，因为刚刚我们没有编写这个文件，所以会使用默认配置，内容如下

# Where are all the schema files located? globs are supported eg  src/**/*.graphqls
schema:
  - graph/*.graphqls

# Where should the generated server code go?
exec:
  filename: graph/generated/generated.go
  package: generated

# Uncomment to enable federation
# federation:
#   filename: graph/generated/federation.go
#   package: generated

# Where should any generated models go?
model:
  filename: graph/model/models_gen.go
  package: model

# Where should the resolver implementations go?
resolver:
  layout: follow-schema
  dir: graph
  package: graph

# Optional: turn on use `gqlgen:"fieldName"` tags in your models
# struct_tag: json

# Optional: turn on to use []Thing instead of []*Thing
# omit_slice_element_pointers: false

# Optional: set to speed up generation time by not performing a final validation pass.
# skip_validation: true

# gqlgen will search for any type names in the schema in these go packages
# if they match it will use them, otherwise it will generate them.
autobind:
  - "test/graph/model"

# This section declares type mapping between the GraphQL and go type systems
#
# The first line in each type will be used as defaults for resolver arguments and
# modelgen, the others will be allowed when binding to fields. Configure them to
# your liking
models:
  ID:
    model:
      - github.com/99designs/gqlgen/graphql.ID
      - github.com/99designs/gqlgen/graphql.Int
      - github.com/99designs/gqlgen/graphql.Int64
      - github.com/99designs/gqlgen/graphql.Int32
  Int:
    model:
      - github.com/99designs/gqlgen/graphql.Int
      - github.com/99designs/gqlgen/graphql.Int64
      - github.com/99designs/gqlgen/graphql.Int32

正是其中的以下代码，指定了读取这个路径文件作为modal文件，而我们没有提供，在刚刚运行才会有validate fail的提示

model:
  filename: graph/model/models_gen.go
  package: model

如果需要，我们也可以创建modal文件夹，在modal文件夹中编写models_gen.go文件，如下，每个字段右侧的 ``注释代表标明json序列化时的键值名称

package model

type NewTodo struct {
	Text   string `json:"text"`
	UserID string `json:"userId"`
}

type Todo struct {
	ID   string `json:"id"`
	Text string `json:"text"`
	Done bool   `json:"done"`
	User *User  `json:"user"`
}

type User struct {
	ID   string `json:"id"`
	Name string `json:"name"`
}

而在graph文件夹中，也生成了对应go代码

Mode                LastWriteTime         Length Name
----                -------------         ------ ----
d-----         2020/5/5     16:08                generated
-a----         2020/5/5     16:08            184 resolver.go
-a----         2020/5/5     11:35             32 schema.graphqls
-a----         2020/5/5     16:08            544 schema.resolvers.go

其中的generated文件夹中包含一个generated.go，是框架的处理逻辑封装，一般由编译生成不去修改，比如刚刚的hello，会被编译为一个接口

type QueryResolver interface {
	Hello(ctx context.Context) (*string, error)
}

我们唯一需要关注的是schema.resolvers.go这个文件，其中定义了每个查询的返回结果，我们需要在其中用golang编写查询结果的实现

package graph

// This file will be automatically regenerated based on the schema, any resolver implementations
// will be copied through when generating and any unknown code will be moved to the end.

import (
	"context"
	"fmt"
	"test/graph/generated"
)

func (r *queryResolver) Hello(ctx context.Context) (*string, error) {
	panic(fmt.Errorf("not implemented"))
}

// Query returns generated.QueryResolver implementation.
func (r *Resolver) Query() generated.QueryResolver { return &queryResolver{r} }

type queryResolver struct{ *Resolver }

像是这个，刚刚的hello在这里被编译为一个go的函数，所以我们通过编写这个函数的实现，决定返回给客户端的内容，比如返回字符串helllo

package graph

import (
	"context"
	"test/graph/generated"
)

func (r *queryResolver) Hello(ctx context.Context) (*string, error) {
	retval := string("hello")
	return &retval,nil
}

func (r *Resolver) Query() generated.QueryResolver { return &queryResolver{r} }

type queryResolver struct{ *Resolver }

运行服务端

实现了查询就可以启动服务端了，在项目根目录执行

go run .\server.go

会看到

connect to http://localhost:8080/ for GraphQL playground

此时访问该地址，就可以看到服务端提供的web查询页面，在左边的输入框编写查询，点击播放按钮即可在右边看到服务端返回的查询结果

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