Non-queryset data ordering in django-tables2 - django

Question

The docs say:
Where the table is backed by a model, the database will handle the ordering. Where this is not the case, the Python cmp function is used and the following mechanism is used as a fallback when comparing across different types: ...
But is this possible in a table that is backed by a model, on a custom column? e.g.
class MyModel(models.Model):
x = models.IntegerField()
y = models.IntegerField()
def z(self):
return x+y
class MyTable(tables.Table):
z = tables.Column()
class Meta:
model = MyModel
When I try something like this, the column displays OK, but when I click on the column header to sort, I get this error:
Caught FieldError while rendering: Cannot resolve keyword u'z' into field. Choices are: ...
Apparently this is because z is not found in the database table.
Is there a way around this?

Answer 1

You can't use a queryset if you're ordering on an attribute that doesn't have a database column. You can pass a list to your table though.
Assuming your models.py looks like this:
from django.db import models
class MyModel(models.Model):
def foo(self):
return something_complex()
You could have tables.py that looks like this:
import django_tables2 as tables
from .models import MyModel
class MyModelTable(tables.Table):
foo = tables.Column()
class Meta:
model = MyModel
Then in your views.py:
from django_tables2.config import RequestConfig
from django.core.paginator import InvalidPage
from django.shortcuts import render
def view_my_models(request):
# use a list so django_tables2 sorts in memory
my_models = list(MyModel.objects.all())
my_models_table = MyModelTable(my_models)
RequestConfig(request).configure(my_models_table)
try:
page_number = int(request.GET.get('page'))
except (ValueError, TypeError):
page_number = 1
try:
my_models_table.paginate(page=page_number, per_page=10)
except InvalidPage:
my_models_table.paginate(page=1, per_page=10)
template_vars = {'table': my_models_table}
return render(response, "view_my_models.html", template_vars)
There's also an open ticket discussing this issue.