[Answer]-In Django registration, if username already exists do something

As suggested in a comment above, you should do it in form’s clean method which would make things easier. But if you must do it in a view, here’s an example:

if request.method == 'POST':
    try:
        user_exists = User.objects.get(username=request.POST['username'])
        return HttpResponse("Username already taken")
    except User.DoesNotExist:
        # Username doesn't exist
        # Do other validation ...

Then show the response in a span using jQuery, or something else.

To get HTTPResponse message, you have to use ajax instead form submit.

Here i am assuming you are using following like html page code.

<input type="text" name="username" id="username"/>  <p id="error"></p>

<input type="button" value="Register" id="register">

Now, You have to make an ajax call on button’s click event like:

(i assume that you have knowledge of ajax call.)

$("#register").on('click', function(){

var username=$("#username").val();

    $.ajax({
    .
    .
    .
    success: fuinction(data){
        if(data=="error occured"){
           $("error").append("wrong username");
    }
    }

    })

    });

and views.py code is like this:

def register(request):
 if request.method == 'POST':
  if User.objects.filter(username = request.POST['username']).exists():
    return HTTPResponse("error occured")

I want to modify an answer from above which can be more easier…. i think 🙂 haha:

def register(request):

    alert = {
        "username": request.GET.get('username', ''),
    }

    if request.method == 'POST':
        username = request.POST.get('username', '')

        if User.objects.filter(username = request.POST['username']).exists():
            alert['username'] = "Username already exists"


    return render(request, 'interface/signup.html', alert)

and in your html: lets just say –>

<form method="POST"> {% csrf_token %}

    <h3>Sign Up</h3>

    <label class="label">Username:</label><input type="text" name="username" class="form-control" /><br>

{% if username %}
    <div class="alert alert-danger alert-dismissible">
        <a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>
        {{ username }}
    </div>
    <br>
{% endif %}
</form>

def register(request):
    form = UserCreationForm(request.POST)
    if form.is_valid():

    else:
        # Form is invalid, this includes the user already existing

I know it’s 2 years late but none of the answers had it and django has a built in way of solving it.