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…

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

1. 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

1. 添加图书

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

1. 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.

1. 更新图书

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

1. 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)
    }
}

Original: https://www.cnblogs.com/cenjw/p/gobeginner-proj-bookstore-cli.html
Author: jvvcen
Title: go入门项目：(1) 基于命令行的图书的增删查改