Lesson 23 — Chainable query builder

Methods that return self

Django lets you write Post.objects.filter(...).order_by(...) because each method returns a QuerySet you can call again. You can build the same fluent (chainable) style yourself: each method changes the data and then does return self.

def reverse(self):
    self.rows = self.rows[::-1]
    return self

Note: the exercise runs in your browser without Django installed, so it is a small plain-Python simulation of what Django does for you.

Why it matters: this is how the ORM stays readable — and knowing it helps you design clean APIs of your own.