How to execute the html template

In this code, I am trying to execute the tmpl.ExecuteTemplate(res, "about.html", d) that is present in the showAbout() function.

In the handler.go file, I have two functions. The first one is showAbout() and the second is about(). about() function check the authorization and after successful authorization, it goes to the showAbout() function in which it has if-statement.

If the about field is empty in the database then it should execute the aboutform.html, take the data and insert it in the database.

If the data is inserted successfully then show the message and go back to about.html to show the data there.

Only about.html is not executing. Although the success message is given.

about.html

<section>
   <h1>About</h1>
   <hr>
   <p>{{.Aboutdata}}</p>
</section>

aboutform.html

<form action="/about" method="POST">
    <section>
        <label>Content</label>
        <textarea name="content"></textarea>
        <div>
            <input type="submit" value="Submit">
        </div>
    </section>
</form>

db.go

func Insertdata(key, value string) bool {
	collection := Connect.Database("webApp3").Collection("data")
	filter := bson.M{"email": Account.Email, "password": Account.Password}
	update := bson.M{
		"$set": bson.M{
			key: value,
		},
	}
	_, err := collection.UpdateOne(context.TODO(), filter, update)
	return err == nil
}

handler.go

func showAbout(res http.ResponseWriter, req *http.Request) {
	d := struct{ Aboutdata string }{Aboutdata: database.Account.About}
	if d.Aboutdata == "" {
		tmpl.ExecuteTemplate(res, "aboutform.html", nil)
		content := req.FormValue("content")
		inserted := database.Insertdata("about", content)
		if inserted == true {
			fmt.Println("About is successfully inserted")
			tmpl.ExecuteTemplate(res, "about.html", d)   // It is not executing the about.html file
		} else {
			fmt.Println("About is not inserted")
		}
	} else {
		tmpl.ExecuteTemplate(res, "about.html", d)    // Although this same file is executing here.
	}
}

func about(res http.ResponseWriter, req *http.Request) {
	session, _ := store.Get(req, "session-name")
	var authenticated interface{} = session.Values["authenticated"]
	if authenticated != nil {
		isAuthenticated := session.Values["authenticated"].(bool)
		if !isAuthenticated {
			tmpl.ExecuteTemplate(res, "login.html", nil)
			return
		}
		showAbout(res, req)
	} else {
		tmpl.ExecuteTemplate(res, "login.html", nil)
		return
	}
}

Here's an example of how your about handler may look like. Keep in mind that the example is just an illustration of a generic structure for handling GET and POST request's with a single handler. From what I can tell the code in your question contains a number of other logical errors that you'll still have to resolve.

Notice that the logic of rendering the template and handling data input is split between the GET and POST HTTP methods. Some routers allow for method-based handler registering in which case you could have two separate handlers, one for showAbout and another for createAbout or something.

The use of return statements in this example is unnecessary given how the if-else blocks are structured, however, I did include them anyway to explicitly illustrate that, in general, after you write to the response once you should not have any other response-writing code: no http.Redirect, no more ExecuteTemplate calls, etc.

func handleAbout(w http.ResponseWriter, r *http.Request) {
    if r.Method == "GET" {
         if data_is_present {
             if err := t.ExecuteTemplate(w, "about.html", nil); err != nil {
                 fmt.Println(err)
             }
             return
         } else if data_is_NOT_present {
             if err := t.ExecuteTemplate(w, "aboutform.html", nil); err != nil {
                 fmt.Println(err)
             }
             return
         }
    } else if r.Method == "POST" {
        content := r.FormValue("content")
        inserted := database.Insertdata("about", content)
        if inserted == true {
            d := struct{ Aboutdata string }{Aboutdata: content}
            if err := t.ExecuteTemplate(w, "about.html", d); err != nil {
                fmt.Println(err)
            }
            return
        } else {
            fmt.Println("About is not inserted")
            return
        }
    }
}