Source code for django.db.models.aggregates

Classes to represent the definitions of aggregate functions.
from django.core.exceptions import FieldError
from django.db.models.expressions import Case, Func, Star, When
from django.db.models.fields import IntegerField
from django.db.models.functions.mixins import (
    FixDurationInputMixin, NumericOutputFieldMixin,

__all__ = [
    'Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance',

[docs]class Aggregate(Func): template = '%(function)s(%(distinct)s%(expressions)s)' contains_aggregate = True name = None filter_template = '%s FILTER (WHERE %%(filter)s)' window_compatible = True allow_distinct = False def __init__(self, *expressions, distinct=False, filter=None, **extra): if distinct and not self.allow_distinct: raise TypeError("%s does not allow distinct." % self.__class__.__name__) self.distinct = distinct self.filter = filter super().__init__(*expressions, **extra) def get_source_fields(self): # Don't return the filter expression since it's not a source field. return [e._output_field_or_none for e in super().get_source_expressions()] def get_source_expressions(self): source_expressions = super().get_source_expressions() if self.filter: return source_expressions + [self.filter] return source_expressions def set_source_expressions(self, exprs): self.filter = self.filter and exprs.pop() return super().set_source_expressions(exprs) def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False): # Aggregates are not allowed in UPDATE queries, so ignore for_save c = super().resolve_expression(query, allow_joins, reuse, summarize) c.filter = c.filter and c.filter.resolve_expression(query, allow_joins, reuse, summarize) if not summarize: # Call Aggregate.get_source_expressions() to avoid # returning self.filter and including that in this loop. expressions = super(Aggregate, c).get_source_expressions() for index, expr in enumerate(expressions): if expr.contains_aggregate: before_resolved = self.get_source_expressions()[index] name = if hasattr(before_resolved, 'name') else repr(before_resolved) raise FieldError("Cannot compute %s('%s'): '%s' is an aggregate" % (, name, name)) return c @property def default_alias(self): expressions = self.get_source_expressions() if len(expressions) == 1 and hasattr(expressions[0], 'name'): return '%s__%s' % (expressions[0].name, raise TypeError("Complex expressions require an alias") def get_group_by_cols(self, alias=None): return [] def as_sql(self, compiler, connection, **extra_context): extra_context['distinct'] = 'DISTINCT ' if self.distinct else '' if self.filter: if connection.features.supports_aggregate_filter_clause: filter_sql, filter_params = self.filter.as_sql(compiler, connection) template = self.filter_template % extra_context.get('template', self.template) sql, params = super().as_sql( compiler, connection, template=template, filter=filter_sql, **extra_context ) return sql, params + filter_params else: copy = self.copy() copy.filter = None source_expressions = copy.get_source_expressions() condition = When(self.filter, then=source_expressions[0]) copy.set_source_expressions([Case(condition)] + source_expressions[1:]) return super(Aggregate, copy).as_sql(compiler, connection, **extra_context) return super().as_sql(compiler, connection, **extra_context) def _get_repr_options(self): options = super()._get_repr_options() if self.distinct: options['distinct'] = self.distinct if self.filter: options['filter'] = self.filter return options
[docs]class Avg(FixDurationInputMixin, NumericOutputFieldMixin, Aggregate): function = 'AVG' name = 'Avg'
[docs]class Count(Aggregate): function = 'COUNT' name = 'Count' output_field = IntegerField() allow_distinct = True def __init__(self, expression, filter=None, **extra): if expression == '*': expression = Star() if isinstance(expression, Star) and filter is not None: raise ValueError('Star cannot be used with filter. Please specify a field.') super().__init__(expression, filter=filter, **extra) def convert_value(self, value, expression, connection): return 0 if value is None else value
[docs]class Max(Aggregate): function = 'MAX' name = 'Max'
[docs]class Min(Aggregate): function = 'MIN' name = 'Min'
[docs]class StdDev(NumericOutputFieldMixin, Aggregate): name = 'StdDev' def __init__(self, expression, sample=False, **extra): self.function = 'STDDEV_SAMP' if sample else 'STDDEV_POP' super().__init__(expression, **extra) def _get_repr_options(self): return {**super()._get_repr_options(), 'sample': self.function == 'STDDEV_SAMP'}
[docs]class Sum(FixDurationInputMixin, Aggregate): function = 'SUM' name = 'Sum'
[docs]class Variance(NumericOutputFieldMixin, Aggregate): name = 'Variance' def __init__(self, expression, sample=False, **extra): self.function = 'VAR_SAMP' if sample else 'VAR_POP' super().__init__(expression, **extra) def _get_repr_options(self): return {**super()._get_repr_options(), 'sample': self.function == 'VAR_SAMP'}