db.models.Aggregate

class Aggregate(expression, output_field=None, **extra) [source]

template

A class attribute, as a format string, that describes the SQL that is generated for this aggregate. Defaults to '%(function)s( %(expressions)s )'.

function

A class attribute describing the aggregate function that will be generated. Specifically, the function will be interpolated as the function placeholder within template. Defaults to None.

The expression argument can be the name of a field on the model, or another expression. It will be converted to a string and used as the expressions placeholder within the template.

The output_field argument requires a model field instance, like IntegerField() or BooleanField(), into which Django will load the value after it’s retrieved from the database. Usually no arguments are needed when instantiating the model field as any arguments relating to data validation (max_length, max_digits, etc.) will not be enforced on the expression’s output value.

Note that output_field is only required when Django is unable to determine what field type the result should be. Complex expressions that mix field types should define the desired output_field. For example, adding an IntegerField() and a FloatField() together should probably have output_field=FloatField() defined.

The **extra kwargs are key=value pairs that can be interpolated into the template attribute.