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What Are Annotations. Django annotations 2 are a way of enriching the objects returned in QuerySets. That is, when you run queries against your models you can ask for new fields, whose values will be dynamically computed, to be added when evaluating the query.

Generating aggregates for each item in a QuerySet Per-object summaries can be generated using the annotate() clause. When an annotate() clause is specified, each object in the QuerySet will be annotated with the specified values. Unlike aggregate() , annotate() is not a terminal clause.

Joins and aggregates When specifying the field to be aggregated in an aggregate function, Django will allow you to use the same double underscore notation that is used when referring to related fields in filters. Django will then handle any table joins that are required to retrieve and aggregate the related value.

Alias() Same as annotate() , but instead of annotating objects in the QuerySet , saves the expression for later reuse with other QuerySet methods. This is useful when the result of the expression itself is not needed but it is used for filtering, ordering, or as a part of a complex expression.

Aggregate calculates values for the entire queryset. Annotate calculates summary values for each item in the queryset.

Difference between annotate() and aggregate(): annotate() aims to evaluate every row in a queryset and create a pseudo field for the same, whereas aggregate() evaluates the queryset as a whole and brings out the final result.

Aggregate calculates values for the entire queryset. Annotate calculates summary values for each item in the queryset.