How to execute multiple variables in HTML Go Template?

Question

I've tried looking at the other questions, and they don't seem to help my situation.

I essentially need to have 2 if statements on my HTML page, but whenever I trigger the second tmpl.Execute() I essentially get the same page embedded within those if statements.

Here is a function that I am trying to get working:

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_)
}

I have commented out the 2 parts that I am trying to get working simultaneously, but they work individually.

Here is the relevant HTML:

                        {{if .Username}}
                        
                        
                        
                           
                           
                              
                                 Select Vehicle 
                                 
                              
                           
                           
                              
                           
                        

                        {{else}}
                         Access Denied, please login.Login
                        {{end}}

I've tried to use a struct, but the carSlice is already a struct and conditionMap is a map.

What would be the best solution to tackling this situation?

mkopriva · Accepted Answer

First off, it is recommended to initialize the *template.Template types and the *sql.DB connection pool only once, during program start up. Both types are safe for concurrent use and can therefore be used by multiple handlers simultaneously.

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)
    }
}

Now your handler can look something like the following:

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)
        }
    }
}

And in your template, since a data passed in by the handler is a map with Username and Vehicles keys, you need to range over .Vehicles and not just the ..

{{if .Username}}



    
    
        
            Select Vehicle 
            
        
    
    
        
    

{{else}}
 Access Denied, please login.Login
{{end}}

How to execute multiple variables in HTML Go Template?

Answers (1)

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