golang - mysql 恐慌：运行时错误：无效的内存地址或 nil 指针取消引用

Question

我尝试使用 golang 建立一个简单的连接并从数据库中获取数据，这里是包含我的 API 试用版的程序：

package main

    

import (
    // "encoding/json"
    "log"
    "net/http"
    "fmt"
    // "math/rand"
    // "strconv"
    "github.com/gorilla/mux"
    "database/sql"
    _ "github.com/go-sql-driver/mysql"
)

// Book Struct(Model)
// type Book struct {
//  ID      string  `json:"id"`
//  Isbn    string  `json:"isbn"`
//  Title   string  `json:"title"`
//  // Author   *Author `json:"author"`
// }

// Article Struct(Model)
type Article struct {
    Author  string  `json:"author"`
    Title   string  `json:"title"`
    Body    string  `json:"body"`
    Created string  `json:"created"`
}

// //Author struct
// type Author struct {
//  Firstname   string  `json:"firstname"`
//  Lastname    string  `json:"lastname"`
// }

// Init books var as a slice book struct
// var books []Book

//get All Books
func getBooks(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    // json.NewEncoder(w).Encode(books)
}
//get single book
func getBook(w http.ResponseWriter, r *http.Request) {
    //
}
//create new book
func createBook(w http.ResponseWriter, r *http.Request) {
    //
}
//get All Books
func updateBook(w http.ResponseWriter, r *http.Request) {
    //
}
//get All Books
func deleteBook(w http.ResponseWriter, r *http.Request) {
    //
}

func main() {
    //init router
    r:= mux.NewRouter()

    //mock Data - @todo - implement DB
    // books = append(books, Book{ID: "1", Isbn: "436455", Title: "Book One", Author: &Author{Firstname: "John", Lastname: "Doe"}})
    // books = append(books, Book{ID: "2", Isbn: "436444", Title: "Book two", Author: &Author{Firstname: "Samuel", Lastname: "Etoo"}})


    db, err := sql.Open("mysql", "root:@tcp(127.0.0.1:3306)/api_golang")
    if err != nil {
        panic(err.Error())
    }

    defer db.Close()

    getarticle, err := db.Query("SELECT * FROM article")


    for getarticle.Next() {
        var article Article

        err = getarticle.Scan(&article.Author)
        if err != nil {
            panic(err.Error())
        }
        fmt.Println(article.Author)
    }
    //Route Handlers
    r.HandleFunc("/api/books", getBooks).Methods("GET")
    r.HandleFunc("/api/books/{id}", getBook).Methods("GET")
    r.HandleFunc("/api/books", createBook).Methods("POST")
    r.HandleFunc("/api/books{id}", updateBook).Methods("PUT")
    r.HandleFunc("/api/books{id}", deleteBook).Methods("DELETE")

    log.Fatal(http.ListenAndServe(":8000", r))
}

这是构建并在 docker 容器中运行程序后的错误报告：

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x618087]

goroutine 1 [running]:
database/sql.(*Rows).Next(0x0)
    /usr/local/go/src/database/sql/sql.go:2944 +0x27
main.main()
    /app/app.go:83 +0x165

我已经确定程序在尝试连接 mysql 数据库时运行良好。

[更新] 对于数据库连接，我使用 xampp for linux，其中包含 apache 和 mysql。所以，数据库不是从 docker 安装的。

Answer 1

1.用密码试试

db, err := sql.Open("mysql",
    "user:password@tcp(127.0.0.1:3306)/test")
if err != nil {
    log.Fatal(err)
}
defer db.Close() 

1. 结构体：文章有4个参数，所以使用“scan”时，“select * from ...”时也需要4个参数。

   “从文章中选择作者”