Introduction

這一年欠的技術債都快還完了，真的是可喜可賀
剛好最近忙完手上的事情就來處理 GraphQL
然後順便練習多用一點英文
GraphQL 的官網介紹蠻詳細的，這篇先做個基本的練習
後面再處理有關認證或資料庫的搭配

What is GraphQL

GraphQL 是一種 API 的查詢語言，使用在數據定義及查詢
GraphQL 不依賴於任何 storage engine 或任何 database，可以想像成專門為『溝通』而產生的 interface
使用 GraphQL 對比 RESTful API 的好處在於

• GraphQL 可以指定欄位查詢，回傳需要的欄位，不像 RESTful API 總是會回傳所有的資料定義，減少網路負載
• 統合各種 frontend framework & platform，不需要因構建平台或環境的不同就要產生新的實作
• 統合數據定義及查詢方法，讓開發更快速
• Schema 即數據定義，可以減少前後端溝通的時間

Sample Code

• Use https://gqlgen.com/ the package for exercise

Initialization

1. Create folder

$ mkdir YourProject
$ cd YourProject
$ code .
$ touch main.go
$ go mod init

2. Important：Tutorial not wroted this step：$ go get github.com/99designs/gqlgen
3. $ go run github.com/99designs/gqlgen init
4. 將 tutorial 內定義好的 schema 貼到 graph/schema.graphqls

type Link {
  id: ID!
  title: String!
  address: String!
  user: User!
}

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

type Query {
  links: [Link!]!
}

input NewLink {
  title: String!
  address: String!
}

input RefreshTokenInput{
  token: String!
}

input NewUser {
  username: String!
  password: String!
}

input Login {
  username: String!
  password: String!
}

type Mutation {
  createLink(input: NewLink!): Link!
  createUser(input: NewUser!): String!
  login(input: Login!): String!
  # we'll talk about this in authentication section
  refreshToken(input: RefreshTokenInput!): String!
}

5. go run github.com/99designs/gqlgen generate

Step 5 失敗的話嘗試 $ go get github.com/99designs/gqlgen
如果正常執行的話會出現

validation failed: packages.Load: /Users/liujinhua/go/src/Go-GraphQL/graph/schema.resolvers.go:53:72: undefined: model.NewTodo
/Users/liujinhua/go/src/Go-GraphQL/graph/schema.resolvers.go:53:89: undefined: model.Todo
/Users/liujinhua/go/src/Go-GraphQL/graph/schema.resolvers.go:56:62: undefined: model.Todo

在把沒有使用到的 function 刪除即可

Implement a Query

What is a Query

a query in graphql is asking for data, you use a query and specify what you want and graphql will return it back to you.

1. 參考 tutorial 實作 schema.resolvers.go 的 Links

func (r *queryResolver) Links(ctx context.Context) ([]*model.Link, error) {
  var links []*model.Link
  dummyLink := model.Link{
    Title: "our dummy link",
    Address: "https://address.org",
    User: &model.User{Name: "admin"},
  }
	links = append(links, &dummyLink)
	return links, nil
}

2. $ go run server.go
3. 用 browser 連線到 http://localhost:8080，或用 Postman 請求 GraphQL
   

Implement a Mutation

What is a Mutation

Simply mutations are just like queries but they can cause a data write, Technically Queries can be used to write data too however it’s not suggested to use it. So mutations are like queries, they have names, parameters and they can return data.

1. 參考 tutorial 實作 schema.resolvers.go 的 CreateLink

func (r *mutationResolver) CreateLink(ctx context.Context, input model.NewLink) (*model.Link, error) {
	var link model.Link
	var user model.User
	link.Address = input.Address
	link.Title = input.Title
	user.Name = "test"
	link.User = &user
	return &link, nil
}

2. $ go run server.go
3. 用 browser 連線到 http://localhost:8080，或用 Postman 請求 GraphQL
   

Reference

• GraphQL：https://graphql.org/
• Learn：https://graphql.org/learn/
• Tutorial：https://www.howtographql.com/graphql-go/1-getting-started/
• Language Reference：https://graphql.org/code/#go
• Why does GraphQL use POST：https://stackoverflow.com/questions/59162265/why-are-graphql-queries-post-requests-even-when-we-are-trying-to-fetch-data-and