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- from django.db.models.expressions import F, OrderBy
-
-
- class OrderableAggMixin:
-
- def __init__(self, expression, ordering=(), **extra):
- if not isinstance(ordering, (list, tuple)):
- ordering = [ordering]
- ordering = ordering or []
- # Transform minus sign prefixed strings into an OrderBy() expression.
- ordering = (
- (OrderBy(F(o[1:]), descending=True) if isinstance(o, str) and o[0] == '-' else o)
- for o in ordering
- )
- super().__init__(expression, **extra)
- self.ordering = self._parse_expressions(*ordering)
-
- def resolve_expression(self, *args, **kwargs):
- self.ordering = [expr.resolve_expression(*args, **kwargs) for expr in self.ordering]
- return super().resolve_expression(*args, **kwargs)
-
- def as_sql(self, compiler, connection):
- if self.ordering:
- ordering_params = []
- ordering_expr_sql = []
- for expr in self.ordering:
- expr_sql, expr_params = expr.as_sql(compiler, connection)
- ordering_expr_sql.append(expr_sql)
- ordering_params.extend(expr_params)
- sql, sql_params = super().as_sql(compiler, connection, ordering=(
- 'ORDER BY ' + ', '.join(ordering_expr_sql)
- ))
- return sql, sql_params + ordering_params
- return super().as_sql(compiler, connection, ordering='')
-
- def set_source_expressions(self, exprs):
- # Extract the ordering expressions because ORDER BY clause is handled
- # in a custom way.
- self.ordering = exprs[self._get_ordering_expressions_index():]
- return super().set_source_expressions(exprs[:self._get_ordering_expressions_index()])
-
- def get_source_expressions(self):
- return self.source_expressions + self.ordering
-
- def get_source_fields(self):
- # Filter out fields contributed by the ordering expressions as
- # these should not be used to determine which the return type of the
- # expression.
- return [
- e._output_field_or_none
- for e in self.get_source_expressions()[:self._get_ordering_expressions_index()]
- ]
-
- def _get_ordering_expressions_index(self):
- """Return the index at which the ordering expressions start."""
- source_expressions = self.get_source_expressions()
- return len(source_expressions) - len(self.ordering)
|
