CODEWITHSUNDEEP
pythondjango
GreenSaber
GreenSaber

Reputation: 1148

Django - Checking if objects exists and raising error if it does

I need to check if an object exists in a table. If the object doesn't exist I want to save it, if it does exist I want to refresh the page and tell the user that the identifier (quote number) already exists. I have this example code:

def some_method(request):
    if request.method == 'POST':
        form = SomeForm(request.POST)
        if form.is_valid:
            quote = request.POST.get('quote')
            if SomeModel.objects.get(quote_number = quote).exists():
               refresh with error #not sure how to do
            else:
               save object #I can do this part

The problem I am running into is that when I check if the object exists (and it does) then the code will raise an error saying the object doesn't exist before it hits the if. Which means on the webpage is full of coding information rather than the refresh with a message for the user.

I want to be able to have a little pop up message or something for the user to enter a new quote number rather than having the developer error page show up.

Am I going about this the correct way?

Upvotes: 1

Views: 7901

Answers (3)

dmvrtx
dmvrtx

Reputation: 168

You can use get_or_create. It returns a tuple with object retrieved (or created) and a boolean value. If boolean value is True when it's a new object, and if it's False when object already exists and you can throw desired error.

Upvotes: 0

4140tm
4140tm

Reputation: 2088

I would do something like this:

from django.http import HttpResponseRedirect
from django.contrib import messages

...

try:
    some_object = SomeModel.objects.get(quote_number=quote)
    message.warning(request, 'some message')
    return HttpResponseRedirect('some-url')
except SomeModel.DoesNotExist:
    some_object = SomeModel.objects.create(quote_number=quote)
    ...

And in the template you can display the message just like so:

{% if messages %}
    {% for message in messages %}
        {{message}}
    {% endfor %}
{% endif %}

Upvotes: 2

Moses Koledoye
Moses Koledoye

Reputation: 78546

The problem is get returns an object, but exists only works with querysets. A Model.DoesNotExist error will be raised when you use get and the object does not exist.

You should use filter instead of get:

qs = SomeModel.objects.filter(quote_number = quote)
if qs.exists():
    ...
else:
    ...

Upvotes: 4

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