Dynamical choices in model's field - django

Question

I want my models to have order field, which will contain order of an item among all items of its kind.
And I want to use choices within that IntegerField, which would contain all the numbers of currently existing items in that table.
So it would need to be dynamic choices.
How do I load all existing "order" values of all existing items in a table, and use this list for choices?

Answer 1

It sounds like you want to build a manager for your model:
models.py
from django.db import models
class OrderManager(models.Manager):
def order_choices(self):
return [(i, i) for i in OrderModel.objects.values_list('order', flat=True)]
class OrderModel(models.Model):
objects = OrderManager()
order = models.IntegerField()
class Meta:
ordering = ['order']
def __unicode__(self):
return '%i' % self.order
forms.py
from django import forms
from yourapp.models import OrderModel
class OrderModelForm(forms.ModelForm):
order = forms.ChoiceField(choices=OrderModel.objects.order_choices())
class Meta:
model = OrderModel
admin.py
from django.contrib import admin
from yourapp.forms import OrderModelForm
from yourapp.models import OrderModel
class OrderModelAdmin(admin.ModelAdmin):
form = OrderModelForm
admin.site.register(OrderModel, OrderModelAdmin)
Edit
Managers are use to make general model queries without having an instance of a model object. If you don't understand the concept of managers, you can still refactor the code out of the manager class, stick it somewhere else and import that function across your code. Managers allow you to abstract custom general queryset that you can reuse. See more details https://docs.djangoproject.com/en/dev/topics/db/managers/
The code without the manager will look like
views.py or some other file
from app.models import OrderModel
def order_choices():
return [(i, i) for i in OrderModel.objects.values_list('order', flat=True)]
From anywhere in your code, if you want to reuse the above multiple times:
from app.views import oder_choices
order_choices()
as opposed to:
from app.models import OderModel
OrderModel.objects.order_choices()
If you only want to use the above once, you can leave it in the forms.py as shown in the other answer. It's really up to you on how you want to refactor your code.

Answer 2

Dont add the choices directly to the model, add them to a form represnting the model later, by overriding the field with a set of choices.
than, do something like:
class MyForm(..):
myfield_order_field = IntegerField(choices = [(i,i) for range(MyModel.objects.count)])
class Meta():
model = MyModel
if you want to use it in the admin, add to your Admin Class:
class MyModelAdmin(admin.ModelAdmin):
...
form = MyForm
it will override this field in the admin too.