Golang和MySQL-管理连接

Question

package main

import (
    "database/sql"
    "fmt"
    _ "github.com/go-sql-driver/mysql"
    "html/template"
    "net/http"
)

var db *sql.DB

var pageTemplate = template.Must(template.ParseFiles("index.html"))

type Items []string

func main() {
    db, err := sql.Open("mysql",
        "username:passwordl@tcp(127.0.0.1:3306)/databasename")
    checkErr(err)
    defer db.Close()
    _, err = db.Exec(
        `
    CREATE TABLE IF NOT EXISTS items (
      item_id INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT,
      item TEXT
    );
    `)
    checkErr(err)
    http.HandleFunc("/", mainHandler)
    http.ListenAndServe(":3000", nil)
}

func mainHandler(w http.ResponseWriter, r *http.Request) {
    var item string
    var items Items
    stmt, err := db.Prepare("select item from items")
    checkErr(err)
    defer stmt.Close()
    rows, err := stmt.Query()
    checkErr(err)
    defer rows.Close()
    for rows.Next() {
        err := rows.Scan(&item)
        checkErr(err)
        items = append(items, item)
    }
    if err = rows.Err(); err != nil {
        checkErr(err)
    }
    pageTemplate.Execute(w, items)
}

func checkErr(err error) {
    if err != nil {
        fmt.Println(err)
    }
}

stmt, err := db.Prepare("select item from items")

如果问题模棱两可，请道歉。

Answer 1

问题是，您在主函数中重新声明了db。

变化：

db, err := sql.Open("mysql",

致：

var err error
db, err = sql.Open("mysql",