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"""
Classes to represent the definitions of aggregate functions.
"""
from django.core.exceptions import FieldError
from django.db.models.expressions import Func, Value
from django.db.models.fields import FloatField, IntegerField
__all__ = [
'Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance',
]
class Aggregate(Func):
contains_aggregate = True
name = None
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
assert len(self.source_expressions) == 1
# Aggregates are not allowed in UPDATE queries, so ignore for_save
c = super(Aggregate, self).resolve_expression(query, allow_joins, reuse, summarize)
if c.source_expressions[0].contains_aggregate and not summarize:
name = self.source_expressions[0].name
raise FieldError("Cannot compute %s('%s'): '%s' is an aggregate" % (
c.name, name, name))
c._patch_aggregate(query) # backward-compatibility support
return c
@property
def input_field(self):
return self.source_expressions[0]
@property
def default_alias(self):
if hasattr(self.source_expressions[0], 'name'):
return '%s__%s' % (self.source_expressions[0].name, self.name.lower())
raise TypeError("Complex expressions require an alias")
def get_group_by_cols(self):
return []
def _patch_aggregate(self, query):
"""
Helper method for patching 3rd party aggregates that do not yet support
the new way of subclassing. This method should be removed in 2.0
add_to_query(query, alias, col, source, is_summary) will be defined on
legacy aggregates which, in turn, instantiates the SQL implementation of
the aggregate. In all the cases found, the general implementation of
add_to_query looks like:
def add_to_query(self, query, alias, col, source, is_summary):
klass = SQLImplementationAggregate
aggregate = klass(col, source=source, is_summary=is_summary, **self.extra)
query.aggregates[alias] = aggregate
By supplying a known alias, we can get the SQLAggregate out of the
aggregates dict, and use the sql_function and sql_template attributes
to patch *this* aggregate.
"""
if not hasattr(self, 'add_to_query') or self.function is not None:
return
placeholder_alias = "_XXXXXXXX_"
self.add_to_query(query, placeholder_alias, None, None, None)
sql_aggregate = query.aggregates.pop(placeholder_alias)
if 'sql_function' not in self.extra and hasattr(sql_aggregate, 'sql_function'):
self.extra['function'] = sql_aggregate.sql_function
if hasattr(sql_aggregate, 'sql_template'):
self.extra['template'] = sql_aggregate.sql_template
class Avg(Aggregate):
function = 'AVG'
name = 'Avg'
def __init__(self, expression, **extra):
super(Avg, self).__init__(expression, output_field=FloatField(), **extra)
def convert_value(self, value, expression, connection, context):
if value is None:
return value
return float(value)
class Count(Aggregate):
function = 'COUNT'
name = 'Count'
template = '%(function)s(%(distinct)s%(expressions)s)'
def __init__(self, expression, distinct=False, **extra):
if expression == '*':
expression = Value(expression)
super(Count, self).__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)
class Max(Aggregate):
function = 'MAX'
name = 'Max'
class Min(Aggregate):
function = 'MIN'
name = 'Min'
class StdDev(Aggregate):
name = 'StdDev'
def __init__(self, expression, sample=False, **extra):
self.function = 'STDDEV_SAMP' if sample else 'STDDEV_POP'
super(StdDev, self).__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)
class Sum(Aggregate):
function = 'SUM'
name = 'Sum'
class Variance(Aggregate):
name = 'Variance'
def __init__(self, expression, sample=False, **extra):
self.function = 'VAR_SAMP' if sample else 'VAR_POP'
super(Variance, self).__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)
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