go入门项目：(1) 基于命令行的图书的增删查改

Go 语言入门练手项目系列

• 01 基于命令行的图书的增删查改
• 02 文件管理
  持续更新中...

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> 本文来自博客园，作者：Arway，转载请注明原文链接：https://www.cnblogs.com/cenjw/p/gobeginner-proj-bookstore-cli.html

介绍

这是一个基于go应用程序命令行的bookstore小项目，具体实现了图书的增删改查，适合刚入门go的朋友熟悉go的语法。

知识点

• go flag，提供了命令行参数解析的功能
• go json的序列化与反序列化
• go ioutil 读写文件

功能演示

1. 列出全部图书

$ .\bookstore.exe get -all
Id      Title                   Author
1       Go语言圣经              Ailen A
2       Java编程思想            Bruce Eckel
3       流畅的Python            Luciano Ramalho
4       PHP权威指南             CENJW

2. 通过id获取相应图书

$ .\bookstore.exe get -id 1
Id      Title           Author
1       Go语言圣经      Ailen A

3. 添加图书

$ .\bookstore.exe add -id 123 -title 'Head First Go' -author unknown
add successfully!

4. 添加图书，如果已经存在相同id的图书，提示已存在

$ .\bookstore.exe add -id 1 -title test -author test 
2022/06/24 18:05:44 Book already exists.

5. 更新图书

$ .\bookstore.exe update -id 123 -title 'head first go' -author UNKNOWN
update successfully!

6. 删除图书

$ .\bookstore.exe delete -id 123
Delete successfully!

本文来自博客园，作者：Arway，转载请注明原文链接：https://www.cnblogs.com/cenjw/p/gobeginner-proj-bookstore-cli.html

功能实现

main.go

func main() {
	// get book/books
	getCmd := flag.NewFlagSet("get", flag.ExitOnError)
	getAll := getCmd.Bool("all", false, "List all books")
	getId := getCmd.String("id", "", "Get a book by id")

	// add/update book
	addCmd := flag.NewFlagSet("add", flag.ExitOnError)
	addId := addCmd.String("id", "", "Book id")
	addTitle := addCmd.String("title", "", "Book title")
	addAuthor := addCmd.String("author", "", "Book author")

	// delete book
	deleteCmd := flag.NewFlagSet("delete", flag.ExitOnError)
	deleteId := deleteCmd.String("id", "", "Book id")
	
	// check command
	if len(os.Args) < 2 {
		log.Fatal("Expected get, add, update, delete commands.")
	}

	switch os.Args[1] {
	case "get":
		handleGetBooks(getCmd, getAll, getId)
	case "add":
		handleAddOrUpdateBook(addCmd, addId, addTitle, addAuthor, true)
	case "update":
		handleAddOrUpdateBook(addCmd, addId, addTitle, addAuthor, false)
	case "delete":
		handleDeleteBook(deleteCmd, deleteId)
	default:
		fmt.Println("Pls provide get, add, update, delete commands.")
	}

}

books.go

type Book struct {
	Id     string `json:"id"`
	Title  string `json:"title"`
	Author string `json:"author"`
}

// get all the books logic
func handleGetBooks(getCmd *flag.FlagSet, all *bool, id *string) {
	getCmd.Parse(os.Args[2:])

	if !*all && *id == "" {
		fmt.Println("subcommand --all or --id needed") // PrintDefault打印集合中所有注册好的flag的默认值。除非另外配置，默认输出到标准错误输出中。
		getCmd.PrintDefaults()
		os.Exit(1)
	}

	if *all {
		books := getBooks()
		fmt.Println("Id\tTitle\t\t\tAuthor\t")
		for _, book := range books {
			fmt.Printf("%v\t%v\t\t%v\t\n", book.Id, book.Title, book.Author)
		}
	}

	if *id != "" {
		var isExist bool
		books := getBooks()
		fmt.Println("Id\tTitle\t\tAuthor\t")
		for _, book := range books {
			if book.Id == *id {
				fmt.Printf("%v\t%v\t%v\t\n", book.Id, book.Title, book.Author)
				isExist = true
			}
		}

		if !isExist {
			log.Fatal("Book not found!")
		}
	}
}

// add or update a book logic
// addBook: true denote add a new book to file, false denote update a book
func handleAddOrUpdateBook(addCmd *flag.FlagSet, id, title, author *string, addBook bool) {
	addCmd.Parse(os.Args[2:])

	if *id == "" || *title == "" || *author == "" {
		addCmd.PrintDefaults()
		log.Fatal("Pls provide id, title, author commands.")
	}
	books := getBooks()
	var newBook Book
	if addBook {
		for _, book := range books {
			if book.Id == *id {
				log.Fatal("Book already exists.")	
			} else {
				newBook = Book{*id, *title, *author}
				books = append(books, newBook)
				break
			}
		}
		
	} else {
		var isExist bool
		for i, book := range books {
			if book.Id == *id {
				books[i] = Book{Id: *id, Title: *title, Author: *author}
				isExist = true
			}
		}

		err := saveBooks(books)
		checkError(err)

		if !isExist {
			log.Fatal("Book not found")
		}

	}

	saveBooks(books)

	fmt.Printf("%s successfully!\n", os.Args[1])
}

func handleDeleteBook(deleteCmd *flag.FlagSet, id *string) {
	deleteCmd.Parse(os.Args[2:])

	if *id == "" {
		deleteCmd.PrintDefaults()
		log.Fatal("Pls provide id command.")
	}

	if *id != "" {
		var isExist bool
		books := getBooks()
		for i, book := range books {
			if book.Id == *id {
				books = append(books[:i], books[i+1:]...)
				isExist = true
			}
		}

		if !isExist {
			log.Fatal("Book not found!")
		}

		err := saveBooks(books)
		checkError(err)

		fmt.Println("Delete successfully!")
	}
}

func saveBooks(books []Book) error {
	bookBytes, err := json.Marshal(books)
	checkError(err)
	err = ioutil.WriteFile("./books.json", bookBytes, 0644)
	return err
}

func getBooks() (books []Book) {
	bookBytes, err := ioutil.ReadFile("./books.json")
	checkError(err)
	err = json.Unmarshal(bookBytes, &books)
	checkError(err)
	return books
}

func checkError(err error) {
	if err != nil {
		log.Fatal("Error happended ", err)
	}
}