raw_id_fields for modelforms

Question

I have a modelform which has one field that is a ForeignKey value to a model which as 40,000 rows. The default modelform tries to create a select box with 40,000 options, which, to say the least is not ideal. Even more so when this modelform is used in a formset factory!

In the admin, this is easiely avoidable by using "raw_id_fields", but there doesn't seem to be a modelform equivalent. How can I do this?

Here is my modelform:

class OpBaseForm(ModelForm):

    base = forms.CharField()

    class Meta:
        model = OpBase
        exclude = ['operation', 'routes']
        extra = 0
        raw_id_fields = ('base', )   #does nothing

The first bolded line works by not creating the huge unwieldy selectbox, but when I try to save a fieldset of this form, I get the error: "OpBase.base" must be a "Base" instance. In order for the modelform to be saved, 'base' needs to be a Base instance. Apparently, a string representation of a Base primary key isn't enough (at least not automatically). I need some kind of mechanism to change the string that is given my the form, to a Base instance. And this mechanism has to work in a formset. Any ideas? If only raw_id_fields would work, this would be easy as cake. But as far as I can tell, it only is available in the admin.

Answer 1

You can also use the entire raw_id_field admin widget, complete with the handy js popup search that the admin page has. You don't even need a model form. Here's how:

import string
from django.contrib.admin.widgets import ForeignKeyRawIdWidget
from django import forms
from models import MyModel

# Have to subclass widget b/c 
# django hardcodes a relative path to Admin Root URL: ../../..
class HardcodedURLForeignKeyRawIdWidget(ForeignKeyRawIdWidget):
    def render(self, *args, **kwargs):
        original_render = super(HardcodedURLForeignKeyRawIdWidget, 
            self).render(*args, **kwargs)
        ADMIN_ROOT_URL = "/admin/"
        return string.replace(original_render,"../../../", ADMIN_ROOT_URL)


class FieldLookupForm(forms.Form):
    my_foreignkey_field = forms.CharField(max_length=10,
        widget=HardcodedURLForeignKeyRawIdWidget(
            MyModel._meta.get_field("foreignkey_field").rel))

Add the relevant admin js to your template, and viola

{% block header %}
<script type="text/javascript">window.__admin_media_prefix__ = "/static/admin/";</script>
<script type="text/javascript" src="/admin/jsi18n/"></script>
<script type="text/javascript" src="/static/admin/js/core.js"></script>
<script type="text/javascript" src="/static/admin/js/admin/RelatedObjectLookups.js"></script>
<script type="text/javascript" src="/static/admin/js/jquery.min.js"></script>
<script type="text/javascript" src="/static/admin/js/jquery.init.js"></script>
<script type="text/javascript" src="/static/admin/js/actions.min.js"></script>
{% endblock %}