67 lines
2.0 KiB
Python
67 lines
2.0 KiB
Python
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"""
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Classes to represent the definitions of aggregate functions.
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"""
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class Aggregate(object):
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"""
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Default Aggregate definition.
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"""
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def __init__(self, lookup, **extra):
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"""Instantiate a new aggregate.
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* lookup is the field on which the aggregate operates.
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* extra is a dictionary of additional data to provide for the
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aggregate definition
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Also utilizes the class variables:
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* name, the identifier for this aggregate function.
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"""
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self.lookup = lookup
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self.extra = extra
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def _default_alias(self):
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return '%s__%s' % (self.lookup, self.name.lower())
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default_alias = property(_default_alias)
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def add_to_query(self, query, alias, col, source, is_summary):
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"""Add the aggregate to the nominated query.
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This method is used to convert the generic Aggregate definition into a
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backend-specific definition.
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* query is the backend-specific query instance to which the aggregate
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is to be added.
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* col is a column reference describing the subject field
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of the aggregate. It can be an alias, or a tuple describing
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a table and column name.
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* source is the underlying field or aggregate definition for
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the column reference. If the aggregate is not an ordinal or
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computed type, this reference is used to determine the coerced
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output type of the aggregate.
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* is_summary is a boolean that is set True if the aggregate is a
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summary value rather than an annotation.
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"""
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aggregate = getattr(query.aggregates_module, self.name)
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query.aggregate_select[alias] = aggregate(col, source=source, is_summary=is_summary, **self.extra)
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class Avg(Aggregate):
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name = 'Avg'
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class Count(Aggregate):
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name = 'Count'
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class Max(Aggregate):
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name = 'Max'
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class Min(Aggregate):
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name = 'Min'
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class StdDev(Aggregate):
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name = 'StdDev'
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class Sum(Aggregate):
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name = 'Sum'
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class Variance(Aggregate):
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name = 'Variance'
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