all(), get() และ filter()

Every model gives you a free objects manager. It is your front door to the database, and every query you write starts from it. 🚪

Call all() to ask for every row in the table. You get back a QuerySet you can loop over, count, or refine further.

A QuerySet looks list-like but it is lazy. Django waits to hit the database until you actually use the results.

Use get() when you expect a single matching row, like one record found by its primary key.

get() is strict. If nothing matches it raises DoesNotExist, so reach for it only when you are sure one row exists.

If get() finds more than one row, it raises MultipleObjectsReturned. It truly means one and only one.

Reach for filter() when you want the rows that match a condition. It returns a QuerySet, even if only one row matches.

Unlike get(), filter() never raises when nothing matches. You simply get an empty QuerySet back instead of an error.

Pass several keyword arguments to filter() and Django joins them with AND. Every condition must be true.

Use get() for one guaranteed object and filter() for a collection. That single choice avoids most beginner query bugs.

Because filter() returns a QuerySet, you can chain calls to narrow results step by step before the database is touched.

You expect a single book and there is no match. Which call raises an error?

Nice work! all() grabs everything, get() fetches one exact row, and filter() returns a subset you can chain. 🎉