Handling PDF Generation and Redirection in Django

You're correct that a single HTTP request can only yield one response in Django. Your current code has two return statements after the form validation, but only the first one (returning the PDF) will execute - the redirect will never happen.

Here are some approaches to solve this problem:

Option 1: JavaScript-based Solution

The most common approach is to serve the PDF in a way that doesn't navigate away from the page, then use JavaScript to redirect after the PDF is handled:

PYTHONCopied
def visitor_vic_signin(request):
    if request.method == "POST":
        form = VisitorFormVic(request.POST)
        if form.is_valid():
            form.save()
            visitor_data = form.cleaned_data
            visitor_name = visitor_data['name']
            
            # Create BytesIO buffer
            buf = io.BytesIO()
            c = canvas.Canvas(buf, pagesize=letter, bottomup=0)
            textob = c.beginText()
            textob.setTextOrigin(inch, inch)
            textob.setFont("Helvetica", 14)
            
            lines = [visitor_name]
            for line in lines:
                textob.textLine(line)
            
            c.drawText(textob)
            c.showPage()
            c.save()
            buf.seek(0)
            
            # Set a session flag to indicate redirection is needed
            request.session['redirect_after_pdf'] = True
            
            # Return the PDF
            return FileResponse(buf, as_attachment=True, filename='visitor_pass.pdf')
    else:
        form = VisitorFormVic()
    
    # Check if we need to redirect after PDF download
    redirect_url = None
    if request.session.pop('redirect_after_pdf', False):
        redirect_url = reverse('visitor_vic_menu')
    
    context = {
        'form': form,
        'redirect_url': redirect_url
    }
    return render(request, "visitor_app/visitor_vic_signin.html", context)

Then in your template, add JavaScript to handle the redirect:

HTMLCopied
{% if redirect_url %}
<script>
    // This will redirect after the page loads (after PDF download)
    window.location.href = "{{ redirect_url }}";
</script>
{% endif %}

Option 2: Serve PDF in a New Window/Tab

Another approach is to open the PDF in a new window/tab while keeping the user on the current page:

PYTHONCopied
def visitor_vic_signin(request):
    if request.method == "POST":
        form = VisitorFormVic(request.POST)
        if form.is_valid():
            form.save()
            
            # Store the visitor ID in session for PDF generation
            request.session['pdf_visitor_id'] = form.instance.id
            
            # Redirect to success page
            return redirect('visitor_vic_menu')
    else:
        form = VisitorFormVic()
    
    context = {'form': form}
    return render(request, "visitor_app/visitor_vic_signin.html", context)

# Add a separate view for PDF generation
def generate_visitor_pdf(request, visitor_id):
    # Get visitor data
    visitor = get_object_or_404(YourVisitorModel, id=visitor_id)
    
    # Create PDF (same code as before)
    buf = io.BytesIO()
    c = canvas.Canvas(buf, pagesize=letter, bottomup=0)
    textob = c.beginText()
    textob.setTextOrigin(inch, inch)
    textob.setFont("Helvetica", 14)
    
    lines = [visitor.name]
    for line in lines:
        textob.textLine(line)
    
    c.drawText(textob)
    c.showPage()
    c.save()
    buf.seek(0)
    
    return FileResponse(buf, as_attachment=True, filename='visitor_pass.pdf')

Then in your success page template, add JavaScript to automatically open the PDF:

HTMLCopied
<script>
    window.onload = function() {
        window.open("{% url 'generate_visitor_pdf' visitor_id %}", "_blank");
    }
</script>

Option 3: AJAX Form Submission

You could also use AJAX to submit the form, then handle both the PDF download and page navigation:

JAVASCRIPTCopied
// In your template
$("#visitor-form").submit(function(e) {
    e.preventDefault();
    
    $.ajax({
        type: "POST",
        url: "{% url 'visitor_vic_signin' %}",
        data: $(this).serialize(),
        success: function(response) {
            if (response.success) {
                // First download the PDF
                window.location.href = response.pdf_url;
                
                // Then redirect after a short delay
                setTimeout(function() {
                    window.location.href = response.redirect_url;
                }, 1000);
            }
        }
    });
});

And modify your view to return JSON:

PYTHONCopied
def visitor_vic_signin(request):
    if request.method == "POST":
        form = VisitorFormVic(request.POST)
        if form.is_valid():
            visitor = form.save()
            
            # Generate PDF and save it to a file
            pdf_path = f"visitor_passes/{visitor.id}.pdf"
            generate_pdf_file(visitor, pdf_path)  # Create this function
            
            # Return JSON response
            return JsonResponse({
                'success': True,
                'pdf_url': reverse('serve_pdf', args=[visitor.id]),
                'redirect_url': reverse('visitor_vic_menu')
            })
    # Rest of the view remains the same

Remember that ReportLab is not thread-safe, as mentioned in the Django documentation, so be cautious when handling multiple concurrent PDF generation requests.