go - 数据库和上下文错误太多

Question

我在“go”代码下运行并收到很多错误:

package main

import (
    "database/sql"
    "log"    
    "github.com/get-ion/ion"
    "github.com/get-ion/ion/context"
    "github.com/get-ion/ion/view"
    _ "github.com/go-sql-driver/mysql"
)

func main() {
    app := ion.New()
    app.RegisterView(view.HTML("./templates", ".html"))

    db, err := sql.Open("mysql", "root:password@/database?charset=utf8&parseTime=true&loc=Local")
    if err != nil {
        log.Fatalln(err)
        panic("There was an error handling mysql connection!")
    }
    defer db.Close()

    allRoutes := app.Party("/", logThisMiddleware)
    {
        allRoutes.Get("/", homePage(db))
    }
}

func logThisMiddleware(ctx context.Context) {
    ctx.Application().Logger().Infof("Path: %s | IP: %s\n", ctx.Path(), ctx.RemoteAddr())
    ctx.Next()
}

func homePage(db *sql.DB) {
    func(ctx context.Context) {
       var (
            id             int
            title          string
            featured_image string
            created_at     string
        )
        rows, err := db.Query("SELECT id, title, featured_image, created_at from blogs order by crated_at desc limit 0,5")
        if err != nil {
            ctx.Application().Logger().Fatalf("MySQL Error fetching row %s\n", err)
        }
        defer rows.Close()
        blogData := map[int]map[int]string{}
        for rows.Next() {
            err := rows.Scan(&id, &title, &featured_image, &created_at)
            if err != nil {
                ctx.Application().Logger().Fatalf("Error while fetching row from blog: %s\n", err)
            }
            blogData[id][0] = title
            blogData[id][1] = featured_image
            blogData[id][2] = created_at
        }
        err = rows.Err()
        if err != nil {
            ctx.Application().Logger().Fatalf("Error while scanning Row : %s\n", err)
        }
        ctx.ViewData("blog", blogData)
        ctx.View("homepage.html")
    }
}

错误是:-

./main.go:40: homePage(db) used as value
./main.go:50: func literal evaluated but not used

所有值都按照以下所述获取:http://go-database-sql.org/retrieving.html ，仍然不确定为什么 undefined variable 问题。我认为不需要创建这些变量，但如果必须创建，请告诉我。

谢谢

Answer 1

./main.go:40: homePage(db) used as value

homePage 是 void 函数。所以你不能在函数参数中使用它。

./main.go:50: func literal evaluated but not used

func homePage(db *sql.DB) {
    func(ctx context.Context) {
        ...
    }
    return ""
}

这是错误的语法。我建议你去https://tour.golang.org/

./main.go:79: too many arguments to return have (string) want ()

正如我在上面所说的，homePage 是 void 函数。所以你不能使用 return with value。以下是我认为您的代码应该是的代码。

package main

import (
    "database/sql"
    "log"

    "github.com/get-ion/ion"
    "github.com/get-ion/ion/context"
    "github.com/get-ion/ion/view"
    _ "github.com/go-sql-driver/mysql"
)

func main() {
    app := ion.New()
    app.RegisterView(view.HTML("./templates", ".html"))

    db, err := sql.Open("mysql", "root:password@/database?charset=utf8&parseTime=true&loc=Local")
    if err != nil {
        log.Fatalln(err)
        panic("There was an error handling mysql connection!")
    }
    defer db.Close()

    allRoutes := app.Party("/", logThisMiddleware)
    {
        allRoutes.Get("/", homePage(db))
    }

    //app.Run(ion.Addr(":8080"))
}

func logThisMiddleware(ctx context.Context) {
    ctx.Application().Logger().Infof("Path: %s | IP: %s\n", ctx.Path(), ctx.RemoteAddr())
    ctx.Next()
}

func homePage(db *sql.DB) context.Handler {
    return func(ctx context.Context) {
        var (
            id             int
            title          string
            featured_image string
            created_at     string
        )
        rows, err := db.Query("SELECT id, title, featured_image, created_at from blogs order by crated_at desc limit 0,5")
        if err != nil {
            ctx.Application().Logger().Fatalf("MySQL Error fetching row %s\n", err)
        }
        defer rows.Close()
        blogData := map[int]map[int]string{}
        for rows.Next() {
            err := rows.Scan(&id, &title, &featured_image, &created_at)
            if err != nil {
                ctx.Application().Logger().Fatalf("Error while fetching row from blog: %s\n", err)
            }
            blogData[id][0] = title
            blogData[id][1] = featured_image
            blogData[id][2] = created_at
        }
        err = rows.Err()
        if err != nil {
            ctx.Application().Logger().Fatalf("Error while scanning Row : %s\n", err)
        }
        ctx.ViewData("blog", blogData)
        ctx.View("homepage.html")
    }
}