aggregate vs annotate
Summarize whole querysets or per-row.
aggregate vs annotate is a free Django Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Django Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Two Ways to Summarize
The ORM gives you two summary tools: aggregate collapses a whole queryset into one result, while annotate adds a value to each row.
What aggregate Returns
Calling aggregate ends the query and hands you a plain Python dictionary, not a queryset, so there is nothing left to filter afterward.
from django.db.models import Avg
Book.objects.aggregate(Avg("price"))
# {"price__avg": 24.5}Naming Your Result
Pass a keyword to aggregate to name the output key yourself, which reads far better than the auto-generated price__avg label.
Book.objects.aggregate(avg_price=Avg("price"))
# {"avg_price": 24.5}Common Aggregate Functions
You get the usual SQL toolkit: Count, Sum, Avg, Min, and Max. Each one rolls the whole queryset down to a single number.
from django.db.models import Count, Sum
Book.objects.aggregate(total=Count("id"), revenue=Sum("price"))What annotate Returns
By contrast, annotate returns a queryset where every object carries a new computed attribute, so you can keep filtering and ordering.
Per-Row Counts
Use annotate with a related count to answer per-object questions, like how many books each author has written.
Author.objects.annotate(num_books=Count("book"))
# each author now has .num_booksGroup By Happens for You
When you annotate over a relation, Django adds the GROUP BY clause automatically, grouping by the model you started from.
Filter on an Annotation
Because annotate keeps a queryset, you can filter on the new value, for example to find authors with more than five books.
Author.objects.annotate(n=Count("book")).filter(n__gt=5)Order by an Annotation
You can also order_by a computed value, so ranking your busiest authors is a one-line query.
Author.objects.annotate(n=Count("book")).order_by("-n")Filter Before You Annotate
Order matters: a filter before annotate narrows which rows get counted, while a filter after it tests the computed result.
Pick the Right Tool
Ask one question: do you want a single summary for the whole set, or one value per object? That choice decides aggregate versus annotate.
Quick Check
You want each author's book count, kept as a queryset you can still order. Which call fits?
Recap
Remember the split: aggregate returns one summary dict and ends the query, while annotate adds a value per row and keeps a queryset you can filter and order. 🎯
Frequently asked questions
Is the “aggregate vs annotate” lesson free?
Yes — the full text of “aggregate vs annotate” is free to read here on the web, and the Django Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Django Academy course, upgrade to CoddyKit PRO.
What will I learn in “aggregate vs annotate”?
Summarize whole querysets or per-row. You practise Django Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Django Academy?
No prior experience is required. Django Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “aggregate vs annotate” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Django Academy lesson?
Yes. Every Django Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.