How do I set the value of a field (which is relevant to form, but not
based directly on the same model) on a modelform when it is displayed
in the admin? I am using the field (with JQuery) to filter the set of
available foreign keys, but want the field to be set when the form
loads an existing record (when it's an add record, it doesn't matter).
Here is a simplified version of what I have (my actual app/model/etc
is more complicated):
* A building has many rooms
* A room has many pieces of equipment
Models:
------------------------------------------------------------
#spaces/models.py
from django.db import models
class Building(models.Model):
name=models.CharField(max_length=32)
def __unicode__(self):
return self.name
class Room(models.Model):
number=models.CharField(max_length=8)
building=models.ForeignKey(Building)
def __unicode__(self):
return self.number
class Equipment(models.Model):
tech = models.CharField(max_length=64)
room = models.ForeignKey(Room)
def __unicode__(self):
return self.tech
------------------------------------------------------------
When adding or editing a piece of equipment, it would be nice to be
able to limit the room choices down (by building). This I can do: I
add a building field to the ModelForm, and then as it gets changed by
the user, JQuery in the template file dynamically updates the list of
rooms. The admin.py part looks like:
------------------------------------------------------------
#spaces/admin.py
from demo.spaces.models import Building, Room, Equipment
from django.contrib import admin
from django import forms
class EquipmentForm(forms.ModelForm):
class Meta:
model = Equipment
building = forms.ModelChoiceField(Building.objects)
class EquipmentAdmin(admin.ModelAdmin):
form = EquipmentForm
admin.site.register(Equipment, EquipmentAdmin)
admin.site.register(Building)
admin.site.register(Room)
------------------------------------------------------------
When adding a new piece of equipment, this all works fine--my JQuery
code displays ----- until a building is selected, at which point the
drop down for the room field is enabled and populated with the
appropriate rooms for that building.
The problem is: when displaying an existing piece of equipment
(demo.com/admin/spaces/equipment/12/) or if the add form doesn't
validate, the Room field properly displays the room --but the building
field is wiped out. The equipment.room foreign key value exists in the
form instance and the admin automagically takes care of setting the
room field to that value, but the value of the building field needs to
be set by me.
I can get the value without a problem, since it's easy in the init of
the form to check for it being an instance, and then traversing back
up to get the value:
------------------------------------------------------------
def __init__(self, *args, **kwargs):
super(EquipmentForm, self).__init__(*args, **kwargs)
if 'instance' in kwargs:
building_value = kwargs['instance'].room.building
------------------------------------------------------------
But what do I do with that value to make the field display it?
I've had two suggestions on stackoverflow--both in the __init__ of the
form:
if 'instance' in kwargs:
self.data['building']=kwargs['instance'].room.building
which didn't help at all (a print statement shows that self.data is
empty at __init__) and then based on a nother suggestion I tried:
if 'instance' in kwargs:
self.initial['building']=kwargs['instance'].room.building
which seems the logical place to do this--since a print self.inital
statement spits back a dictionary of all the fields and their values
({'tech':u'Projector', 'room':u'101'})--and inserting the looked-up
value of the building field into this list seems like the right
place. But it doesn't do it.
The only thing I haven't tried yet is adding more code in my template
to use Jquery to get the value and set it at the end, but I'd rather
not have to have the javascript in the page hit the database to figure
display the value, since it seems like something that should be done
when the form is rendered...
Any thoughts? Thank you for you help!
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