在 HTML Go 模板中如何同时执行多个变量？

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我尝试过查看其他问题，但它们似乎对我的情况没有帮助。

我的 html 页面上基本上需要有 2 个 if 语句，但是每当我触发第二个 tmpl.execute() 时，我基本上会在这些 if 语句中嵌入相同的页面。

这是我正在尝试实现的一个功能：

func removevehicle(w http.responsewriter, r *http.request) {

    conditionsmap := map[string]interface{}{}

    username, _ := extracttokenusername(r)

    if username != "" {
        conditionsmap["username"] = username
    }

    t, err := template.parsefiles("remove.html")
    if err != nil {
        http.error(w, err.error(), 500)
        return
    }
    if r.method != http.methodpost {
        t.execute(w, conditionsmap) //here i am trying to check to see if the user is logged in, and if not to return a false boolean that will trigger the else statement
        return
    }

    db, err := sql.open("mysql", "root:*******@tcp(127.0.0.1:3306)/my_db")

    if err != nil {
        fmt.println("connection failed.")
        panic(err.error())
    }

    defer db.close()

    var car vehicle
    sqlstatement := `select * from vehicle`
    rows, err := db.query(sqlstatement)
    if err != nil {
        panic(err)
    }
    defer rows.close()

    var carslice []vehicle
    for rows.next() {
        rows.scan(&car.id, &car.date, &car.brand, &car.model, &car.mileage, &car.year, &car.rented, &car.dayrate)
        carslice = append(carslice, car)
    }

    if r.method != http.methodpost {
        t.execute(w, carslice) // then here i am trying to populate the form select with a few rows from a table
        return
    }

    var id_ = r.formvalue("select")
    fmt.println(id_)

    stmt, e := db.prepare("delete from vehicle where id=?")
    errorcheck(e)

    stmt.exec(id_)
}

我已经注释掉了我试图同时工作的两个部分，但它们是单独工作的。

以下是相关的 html：

{{if .Username}}
                        <div><img src="images/kogdpilnmzhz9rhzceo2.png" alt="" width="65" height="65" class="addV_label"/></div>
                        <hr style="height:5px">
                        <form action="/remove" method="POST" source="custom" name="form">
                           &lt;input type=&quot;hidden&quot; name=&quot;xss-token&quot; value=&quot;&quot;/&gt;
                           <div class="form-group">
                              <div>
                                 <label class="addV_label">Select Vehicle&nbsp;</label>
                                 &lt;select name=&quot;select&quot; class=&quot;form-control loginInput2&quot; required=&quot;required&quot;&gt;

                                    {{range .}}
                                    <option value="{{.Id}}">{{.Brand}} {{.Model}} ({{.Year}}), {{.Mileage}} miles | £{{.Dayrate}}/pd</option>
                                    {{end}}

                                 &lt;/select&gt;
                              </div>
                           </div>
                           <div>
                              <button class="btn-block frgt_1 btn addV_btn" type="submit" value="remove">REMOVE</button>
                           </div>
                        </form>

                        {{else}}
                        <p> Access Denied, please login.<a href="/login">Login</a></p>
                        {{end}}

我尝试使用结构，但 carslice 已经是一个结构，而 conditionmap 是一个地图。

解决这种情况的最佳解决方案是什么？

正确答案

首先，建议在程序启动期间仅初始化 *template.template 类型和 *sql.db 连接池一次。这两种类型对于并发使用都是安全的，因此可以由多个处理程序同时使用。

var (
    removetemplate *template.template
    db             *sql.db
)

func init() {
    var err error

    removetemplate, err = template.parsefiles("remove.html")
    if err != nil {
        panic(err)
    }

    db, err = sql.open("mysql", "root:*******@tcp(127.0.0.1:3306)/my_db")
    if err != nil {
        panic(err)
    } else if err := db.ping(); err != nil {
        panic(err)
    }
}

现在您的处理程序可能如下所示：

func removevehicle(w http.responsewriter, r *http.request) {
    // check if the user is logged in
    username, _ := extracttokenusername(r)
    if len(username) == 0 {
        // if not, render the template with no data, this
        // will show the "please login" part of your template
        if err := removetemplate.execute(w, nil); err != nil {
            http.error(w, err.error(), http.statusinternalservererror)
        }
        return
    }

    switch r.method {

    // if the method is get, show the list of vehicles available
    case http.methodget:
        // select vehicles from db
        rows, err := db.query(`select * from vehicle`)
        if err != nil {
            http.error(w, err.error(), http.statusinternalservererror)
            return
        }
        defer rows.close()

        // scan rows
        var vehicles []vehicle
        for rows.next() {
            var v vehicle
            err := rows.scan(&v.id, &v.date, &v.brand, &v.model, &v.mileage, &v.year, &v.rented, &v.dayrate)
            if err != nil {
                http.error(w, err.error(), http.statusinternalservererror)
                return
            }
            vehicles = append(vehicles, v)
        }
        if err := rows.err(); err != nil {
            http.error(w, err.error(), http.statusinternalservererror)
            return
        }

        // now render the template with the data
        // that you just retrieved from the database
        data := map[string]interface{}{
            "username": username,
            "vehicles": vehicles,
        }
        if err := removetemplate.execute(w, data); err != nil {
            http.error(w, err.error(), http.statusinternalservererror)
        }

    // if the method is post, delete the vehicle
    case http.methodpost {
        var id = r.formvalue("select")
        if _, err := db.exec("delete from vehicle where id=?", id); err != nil {
            http.error(w, err.error(), http.statusinternalservererror)
        }
    }
}

在您的模板中，由于处理程序传入的数据是带有 username 和 vehicles 键的映射，因此您需要 range 覆盖 .vehicles 而不仅仅是 .。

{{if .Username}}
<div><img src="images/kogdpilnmzhz9rhzceo2.png" alt="" width="65" height="65" class="addV_label"/></div>
<hr style="height:5px">
<form action="/remove" method="POST" source="custom" name="form">
    &lt;input type=&quot;hidden&quot; name=&quot;xss-token&quot; value=&quot;&quot;/&gt;
    <div class="form-group">
        <div>
            <label class="addV_label">Select Vehicle&nbsp;</label>
            &lt;select name=&quot;select&quot; class=&quot;form-control loginInput2&quot; required=&quot;required&quot;&gt;
                {{range .Vehicles}}
                <option value="{{.Id}}">{{.Brand}} {{.Model}} ({{.Year}}), {{.Mileage}} miles | £{{.Dayrate}}/pd</option>
                {{end}}
            &lt;/select&gt;
        </div>
    </div>
    <div>
        <button class="btn-block frgt_1 btn addV_btn" type="submit" value="remove">REMOVE</button>
    </div>
</form>
{{else}}
<p> Access Denied, please login.<a href="/login">Login</a></p>
{{end}}

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