Filtering QuerySets

Filtering is like telling the filing cabinet 'only show me the cards where the name starts with A', instead of dumping every card on the table.

In this page:

Model.objects.filter(field=value) returns only the rows where that field matches the given value, as a new QuerySet.

Example: Basic Filtering

Model.objects.filter(field=value) returns only the rows where that field matches the given value, as a new QuerySet.

bash

action_books = Book.objects.filter(genre='Action')
for book in action_books:
    print(book.title)

⚠️ Run this command in your terminal.

Passing multiple keyword arguments to .filter() combines them with AND logic — every condition must match.

Example: Filtering on Multiple Fields

Passing multiple keyword arguments to .filter() combines them with AND logic — every condition must match.

bash

books = Book.objects.filter(genre='Action', pages__gt=100)
for book in books:
    print(book.title, book.pages)

⚠️ Run this command in your terminal.

Because .filter() returns a QuerySet, you can call .filter() again on the result to add more conditions step by step.

Example: Chaining Filters

Because .filter() returns a QuerySet, you can call .filter() again on the result to add more conditions step by step.

bash

qs = Book.objects.filter(genre='Action')
qs = qs.filter(pages__gt=100)
print(qs.count())

⚠️ Run this command in your terminal.

Common Mistakes

Using .get() when multiple rows could match, instead of .filter(), which raises MultipleObjectsReturned.
Chaining unrelated conditions across separate .filter() calls when a single combined filter would be clearer and faster.
Filtering in Python after fetching everything with .all(), instead of letting the database do the filtering with .filter().

Chapter Summary

.filter(field=value) returns a QuerySet containing only the rows that match the condition.
You can filter on multiple fields at once by passing several keyword arguments.
Filtering happens in the database, which is far more efficient than filtering in Python.
Filters can be chained together to progressively narrow down a QuerySet.

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