CODEWITHSUNDEEP
djangodjango-forms
Jeff Tratner
Jeff Tratner

Reputation: 17116

Form/ModelForm instances between requests

I want write a custom form field (and possibly widget too) and I'm not sure about how the form instances are shared between requests. For example, if I render a form with data from a model instance, is that instance still available when I am validating data? If so, does that mean that there is another database hit to look up the model again between requests?

Similarly, if I write a custom field that takes in a list of data to display in its __init__ method, will that list of data be available to validate against when the user POSTs the data?

It would be really helpful if someone could point me to parts of the django source where this occurs. I've been looking at the models.py, forms.py, fields.py and widgets.py from django.forms, but I'm still not 100% sure how it all works out.

Eventually, what I want to do is have a field that works something like this (the key part is the last line):

class CustomField(ChoiceField):
    def __init__(self, data_dict, **kwargs):
        super(CustomField, self).__init__(**kwargs)
        self.data_dict = data_dict
        self.choices = data_dict.keys()
    def validate(self, value):
        if value not in self.data_dict:
            raise ValidationError("Invalid choice")
        else:
            return self.data_dict[value]

Will that data_dict be available on the next request? If I create a custom forms.Form and initialize it with the data_dict, will that be available on the next request? (e.g. with a factory method or something...).

Side note: I'm doing this because I want to (eventually) use something like Bootstrap's typeahead and I'd like to pass it "pretty values" which I then convert server-side (basically, like how option values in a select can have a different submitted value). I've done this with client-side javascript in the past, but it would be nice to consolidate it all into a form field.

Upvotes: 2

Views: 135

Answers (1)

Daniel Roseman
Daniel Roseman

Reputation: 599876

There's nothing magical about forms. Like everything else in Django (or just about any web framework), objects don't persist between requests, and need to be reinstantiated each time. This happens in the normal view pattern for form handling: you instantiate it once for a POST, and a separate time for a GET. If you have data associated with the form, it would need to be passed in each time.

Upvotes: 2

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