iommi vs inheritance explosion
2024-09-30
A common pattern in OOP when you need to customize some libraries functionality is that you get an inheritance explosion. Let’s look at an example from the django-tables2 documentation:
from django_filters.views import FilterView
from django_tables2.views import SingleTableMixin
from django_filters import FilterSet, CharFilter
from django.forms import Widget
from .models import Person
class PersonTable(tables.Table):
class Meta:
model = Person
class PersonNumberWidget(Widget):
def format_value(self, value):
return f'{value[:-4]}-{value[-4:]}'
class PersonFilter(FilterSet):
class Meta:
model = Person
fields = {
"name": ["contains"],
"country": ["contains"],
}
person_number = CharFilter(
widget=PersonNumberWidget(),
)
def __init__(self, *args, **kwargs):
super(SaleFilter, self).__init__(*args, **kwargs)
self.filters['name'].label = "Name of the person"
class FilteredPersonListView(SingleTableMixin, FilterView):
table_class = PersonTable
model = Person
template_name = "template.html"
filterset_class = PersonFilter
(The code for template.html omitted for brevity.)
This code creates a table for the model Person and turns on filtering for the name and country fields. it also formats the person number with a dash before the last four digits as expected for Sweden. Three classes for a very simple view.
In iommi the same functionality looks like this:
class PersonTable(Table):
class Meta:
auto__model = Person
columns = dict(
name__filter__include=True,
name__display_name='Name of the person',
country__filter__include=True,
person_number__cell__format=lambda value, **_:
f'{value[:-4]}-{value[-4:]}'
)
This is accomplished via Refinable objects, and Transparent APIs.