# Django 4.2.11 documentation

# Source code for django.db.models.aggregates

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

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

    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
        empty_result_set_value = None

        def __init__(
            self, *expressions, distinct=False, filter=None, default=None, **extra
        ):
            if distinct and not self.allow_distinct:
                raise TypeError("%s does not allow distinct." % self.__class__.__name__)
            if default is not None and self.empty_result_set_value is not None:
                raise TypeError(f"{self.__class__.__name__} does not allow default.")
            self.distinct = distinct
            self.filter = filter
            self.default = default
            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 summarize:
                # Summarized aggregates cannot refer to summarized aggregates.
                for ref in c.get_refs():
                    if query.annotations[ref].is_summary:
                        raise FieldError(
                            f"Cannot compute {c.name}('{ref}'): '{ref}' is an aggregate"
                        )
            elif not self.is_summary:
                # 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 = (
                            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)
                        )
            if (default := c.default) is None:
                return c
            if hasattr(default, "resolve_expression"):
                default = default.resolve_expression(query, allow_joins, reuse, summarize)
                if default._output_field_or_none is None:
                    default.output_field = c._output_field_or_none
            else:
                default = Value(default, c._output_field_or_none)
            c.default = None  # Reset the default argument before wrapping.
            coalesce = Coalesce(c, default, output_field=c._output_field_or_none)
            coalesce.is_summary = c.is_summary
            return coalesce

        @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 []

        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:
                    try:
                        filter_sql, filter_params = self.filter.as_sql(compiler, connection)
                    except FullResultSet:
                        pass
                    else:
                        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

    class Avg(FixDurationInputMixin, NumericOutputFieldMixin, Aggregate):
        function = "AVG"
        name = "Avg"
        allow_distinct = True

    class Count(Aggregate):
        function = "COUNT"
        name = "Count"
        output_field = IntegerField()
        allow_distinct = True
        empty_result_set_value = 0

        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)

    class Max(Aggregate):
        function = "MAX"
        name = "Max"

    class Min(Aggregate):
        function = "MIN"
        name = "Min"

    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"}

    class Sum(FixDurationInputMixin, Aggregate):
        function = "SUM"
        name = "Sum"
        allow_distinct = True

    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"}