Django-tables2: how to order_by accessor

Question

Say we have a column like:

num_member = tables.Column(accessor = 'members.count', verbose_name = 'number of members' )

When I tried to sort this in the template, it raises:

Field Error: Cannot resolve keyword u'count' into field

I read the document and it says we can use order_by by passing in some sort of accessor, but how exactly do we do this please?

Answer 1

For function like Model's property method, you can access it directly using accessor. For example:

Class MyModel(models.Model):
    data= models.CharField(max_length=255)

    @property
    def print_function(self):
       return 'hello world'

#Table class
class MyTable(tables.Table):
        data= tables.Column(accessor='print_function')

    class Meta:
        model = MyModel
        fields = ('data')

Using the above method, you can show different kinds of data in table using accessor:

Class SomeModel(models.Model):
    some_data= models.CharField(max_length=255)
    data= models.ManyToManyField(MyModel)

    @property
    def count_function(self):
       some_data= self.data.objects.count() #returns count of the objects
       return some_data

#Table class
class SomeTable(tables.Table):
    data= tables.Column(accessor='count_function')

    class Meta:
        model = SomeModel
        fields = ('data')

And accessor can be used for directly accessing related foreignkey model's field value like:

Class SomeModel(models.Model):
    somedata= models.ForeignKey(MyModel)


#Table class
class MyTable(tables.Table):
        data= tables.Column(accessor='somedata.data')

    class Meta:
        model = SomeModel
        fields = ('data')

EDIT

Lets give an example of how order_by can be used:

#Class Based view, I am subclassing ListView and SingleTableView here for example

class MyView(ListView, SingleTableView):
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['table'].order_by = '-last_updated' #last_updated is a datetimefield in model
        return context

In the above code, what I have done is that, I am changing the order of the table data in context which will later be rendered in template.