What is the difference between aggregation and annotation in Django?

What is the difference between aggregation and annotation in Django?

In Django, aggregation is used to compute a single value from a set of values, like counting or averaging. Annotation, on the other hand, adds a new field to each object in a queryset, allowing you to include calculated values alongside the original data.

Can you give me an example of each?

Sure! For aggregation, you might use MyModel.objects.aggregate(Avg('field_name')) to get the average of a field. For annotation, you could use MyModel.objects.annotate(new_field=Count('related_model')) to add a count of related objects to each instance.

When should I use aggregation over annotation?

Use aggregation when you need a summary value for a group of records, and use annotation when you want to enrich each record with additional calculated data.

Are there any performance considerations I should be aware of?

Yes, aggregation can be more efficient for large datasets since it reduces the amount of data returned. Annotation can be more resource-intensive as it adds calculations to each record.