How to execute multiple variables in HTML Go Template? - go

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}}
<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">
<input type="hidden" name="xss-token" value=""/>
<div class="form-group">
<div>
<label class="addV_label">Select Vehicle </label>
<select name="select" class="form-control loginInput2" required="required">
{{range .}}
<option value="{{.Id}}">{{.Brand}} {{.Model}} ({{.Year}}), {{.Mileage}} miles | £{{.Dayrate}}/pd</option>
{{end}}
</select>
</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.Login</p>
{{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?

Answer 1

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}}
<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">
<input type="hidden" name="xss-token" value=""/>
<div class="form-group">
<div>
<label class="addV_label">Select Vehicle </label>
<select name="select" class="form-control loginInput2" required="required">
{{range .Vehicles}}
<option value="{{.Id}}">{{.Brand}} {{.Model}} ({{.Year}}), {{.Mileage}} miles | £{{.Dayrate}}/pd</option>
{{end}}
</select>
</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.Login</p>
{{end}}