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"""
Classes to represent the default SQL aggregate functions
"""
import copy
import warnings
from django.db.models.fields import FloatField, IntegerField
from django.db.models.lookups import RegisterLookupMixin
from django.utils.deprecation import RemovedInDjango20Warning
from django.utils.functional import cached_property
__all__ = ['Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance']
warnings.warn(
"django.db.models.sql.aggregates is deprecated. Use "
"django.db.models.aggregates instead.",
RemovedInDjango20Warning, stacklevel=2)
class Aggregate(RegisterLookupMixin):
"""
Default SQL Aggregate.
"""
is_ordinal = False
is_computed = False
sql_template = '%(function)s(%(field)s)'
def __init__(self, col, source=None, is_summary=False, **extra):
"""Instantiate an SQL aggregate
* col is a column reference describing the subject field
of the aggregate. It can be an alias, or a tuple describing
a table and column name.
* source is the underlying field or aggregate definition for
the column reference. If the aggregate is not an ordinal or
computed type, this reference is used to determine the coerced
output type of the aggregate.
* extra is a dictionary of additional data to provide for the
aggregate definition
Also utilizes the class variables:
* sql_function, the name of the SQL function that implements the
aggregate.
* sql_template, a template string that is used to render the
aggregate into SQL.
* is_ordinal, a boolean indicating if the output of this aggregate
is an integer (e.g., a count)
* is_computed, a boolean indicating if this output of this aggregate
is a computed float (e.g., an average), regardless of the input
type.
"""
self.col = col
self.source = source
self.is_summary = is_summary
self.extra = extra
# Follow the chain of aggregate sources back until you find an
# actual field, or an aggregate that forces a particular output
# type. This type of this field will be used to coerce values
# retrieved from the database.
tmp = self
while tmp and isinstance(tmp, Aggregate):
if getattr(tmp, 'is_ordinal', False):
tmp = self._ordinal_aggregate_field
elif getattr(tmp, 'is_computed', False):
tmp = self._computed_aggregate_field
else:
tmp = tmp.source
self.field = tmp
# Two fake fields used to identify aggregate types in data-conversion operations.
@cached_property
def _ordinal_aggregate_field(self):
return IntegerField()
@cached_property
def _computed_aggregate_field(self):
return FloatField()
def relabeled_clone(self, change_map):
clone = copy.copy(self)
if isinstance(self.col, (list, tuple)):
clone.col = (change_map.get(self.col[0], self.col[0]), self.col[1])
return clone
def as_sql(self, compiler, connection):
"Return the aggregate, rendered as SQL with parameters."
params = []
if hasattr(self.col, 'as_sql'):
field_name, params = self.col.as_sql(compiler, connection)
elif isinstance(self.col, (list, tuple)):
field_name = '.'.join(compiler(c) for c in self.col)
else:
field_name = compiler(self.col)
substitutions = {
'function': self.sql_function,
'field': field_name
}
substitutions.update(self.extra)
return self.sql_template % substitutions, params
def get_group_by_cols(self):
return []
@property
def output_field(self):
return self.field
class Avg(Aggregate):
is_computed = True
sql_function = 'AVG'
class Count(Aggregate):
is_ordinal = True
sql_function = 'COUNT'
sql_template = '%(function)s(%(distinct)s%(field)s)'
def __init__(self, col, distinct=False, **extra):
super(Count, self).__init__(col, distinct='DISTINCT ' if distinct else '', **extra)
class Max(Aggregate):
sql_function = 'MAX'
class Min(Aggregate):
sql_function = 'MIN'
class StdDev(Aggregate):
is_computed = True
def __init__(self, col, sample=False, **extra):
super(StdDev, self).__init__(col, **extra)
self.sql_function = 'STDDEV_SAMP' if sample else 'STDDEV_POP'
class Sum(Aggregate):
sql_function = 'SUM'
class Variance(Aggregate):
is_computed = True
def __init__(self, col, sample=False, **extra):
super(Variance, self).__init__(col, **extra)
self.sql_function = 'VAR_SAMP' if sample else 'VAR_POP'
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