Alternative column ordering

When using queryset data, one might want to show a computed value which is not in the database. In this case, attempting to order the column will cause an exception:

# models.py
class Person(models.Model):
    first_name = models.CharField(max_length=200)
    family_name = models.CharField(max_length=200)

    @property
    def name(self):
        return '{} {}'.format(self.first_name, self.family_name)

# tables.py
class PersonTable(tables.Table):
    name = tables.Column()
>>> table = PersonTable(Person.objects.all())
>>> table.order_by = 'name'
>>>
>>> # will result in:
FieldError: Cannot resolve keyword 'name' into field. Choices are: first_name, family_name

To prevent this, django-tables2 allows two ways to specify custom ordering: accessors and order_FOO() methods.

Ordering by accessors

You can supply an order_by argument containing a name or a tuple of the names of the columns the database should use to sort it:

class PersonTable(tables.Table):
    name = tables.Column(order_by=('first_name', 'family_name'))

Accessor syntax can be used as well, as long as they point to a model field.

If ordering does not make sense for a particular column, it can be disabled via the orderable argument:

class SimpleTable(tables.Table):
    name = tables.Column()
    actions = tables.Column(orderable=False)

table.order_FOO() methods

Another solution for alternative ordering is being able to chain functions on to the original queryset. This method allows more complex functionality giving the ability to use all of Django’s QuerySet API.

Adding a Table.order_FOO method (where FOO is the name of the column), gives you the ability to chain to, or modify, the original queryset when that column is selected to be ordered.

The method takes two arguments: queryset, and is_descending. The return must be a tuple of two elements. The first being the queryset and the second being a boolean; note that modified queryset will only be used if the boolean is True.

For example, let’s say instead of ordering alphabetically, ordering by amount of characters in the first_name is desired. The implementation would look like this:

# tables.py
from django.db.models.functions import Length

class PersonTable(tables.Table):
    name = tables.Column()

    def order_name(self, queryset, is_descending):
        queryset = queryset.annotate(
            length=Length('first_name')
        ).order_by(('-' if is_descending else '') + 'length')
        return (queryset, True)

As another example, presume the situation calls for being able to order by a mathematical expression. In this scenario, the table needs to be able to be ordered by the sum of both the shirts and the pants. The custom column will have its value rendered using Table.render_foo methods.

This can be achieved like this:

# models.py
class Person(models.Model):
    first_name = models.CharField(max_length=200)
    family_name = models.CharField(max_length=200)
    shirts = models.IntegerField()
    pants = models.IntegerField()


# tables.py
from django.db.models import F

class PersonTable(tables.Table):
    clothing = tables.Column()

    class Meta:
        model = Person

    def render_clothing(self, record):
        return str(record.shirts + record.pants)

    def order_clothing(self, queryset, is_descending):
        queryset = queryset.annotate(
            amount=F('shirts') + F('pants')
        ).order_by(('-' if is_descending else '') + 'amount')
        return (queryset, True)