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 Func, Star
from django.db.models.fields import DecimalField, FloatField, IntegerField

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


[docs]class Aggregate(Func): contains_aggregate = True name = None 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) if not summarize: expressions = c.get_source_expressions() for index, expr in enumerate(expressions): if expr.contains_aggregate: before_resolved = self.get_source_expressions()[index] name = before_resolved.name if hasattr(before_resolved, 'name') else repr(before_resolved) raise FieldError("Cannot compute %s('%s'): '%s' is an aggregate" % (c.name, 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, self.name.lower()) raise TypeError("Complex expressions require an alias") def get_group_by_cols(self): return []
[docs]class Avg(Aggregate): function = 'AVG' name = 'Avg' def _resolve_output_field(self): source_field = self.get_source_fields()[0] if isinstance(source_field, (IntegerField, DecimalField)): self._output_field = FloatField() super()._resolve_output_field() def as_oracle(self, compiler, connection): if self.output_field.get_internal_type() == 'DurationField': expression = self.get_source_expressions()[0] from django.db.backends.oracle.functions import IntervalToSeconds, SecondsToInterval return compiler.compile( SecondsToInterval(Avg(IntervalToSeconds(expression))) ) return super().as_sql(compiler, connection)
[docs]class Count(Aggregate): function = 'COUNT' name = 'Count' template = '%(function)s(%(distinct)s%(expressions)s)' def __init__(self, expression, distinct=False, **extra): if expression == '*': expression = Star() super().__init__( expression, distinct='DISTINCT ' if distinct else '', output_field=IntegerField(), **extra ) def __repr__(self): return "{}({}, distinct={})".format( self.__class__.__name__, self.arg_joiner.join(str(arg) for arg in self.source_expressions), 'False' if self.extra['distinct'] == '' else 'True', ) def convert_value(self, value, expression, connection, context): if value is None: return 0 return int(value)
[docs]class Max(Aggregate): function = 'MAX' name = 'Max'
[docs]class Min(Aggregate): function = 'MIN' name = 'Min'
[docs]class StdDev(Aggregate): name = 'StdDev' def __init__(self, expression, sample=False, **extra): self.function = 'STDDEV_SAMP' if sample else 'STDDEV_POP' super().__init__(expression, output_field=FloatField(), **extra) def __repr__(self): return "{}({}, sample={})".format( self.__class__.__name__, self.arg_joiner.join(str(arg) for arg in self.source_expressions), 'False' if self.function == 'STDDEV_POP' else 'True', ) def convert_value(self, value, expression, connection, context): if value is None: return value return float(value)
[docs]class Sum(Aggregate): function = 'SUM' name = 'Sum' def as_oracle(self, compiler, connection): if self.output_field.get_internal_type() == 'DurationField': expression = self.get_source_expressions()[0] from django.db.backends.oracle.functions import IntervalToSeconds, SecondsToInterval return compiler.compile( SecondsToInterval(Sum(IntervalToSeconds(expression))) ) return super().as_sql(compiler, connection)
[docs]class Variance(Aggregate): name = 'Variance' def __init__(self, expression, sample=False, **extra): self.function = 'VAR_SAMP' if sample else 'VAR_POP' super().__init__(expression, output_field=FloatField(), **extra) def __repr__(self): return "{}({}, sample={})".format( self.__class__.__name__, self.arg_joiner.join(str(arg) for arg in self.source_expressions), 'False' if self.function == 'VAR_POP' else 'True', ) def convert_value(self, value, expression, connection, context): if value is None: return value return float(value)