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49 lines
2.0 KiB
Python
49 lines
2.0 KiB
Python
5 years ago
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from django.db.models.expressions import F, OrderBy
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class OrderableAggMixin:
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def __init__(self, *expressions, ordering=(), **extra):
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if not isinstance(ordering, (list, tuple)):
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ordering = [ordering]
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ordering = ordering or []
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# Transform minus sign prefixed strings into an OrderBy() expression.
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ordering = (
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(OrderBy(F(o[1:]), descending=True) if isinstance(o, str) and o[0] == '-' else o)
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for o in ordering
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)
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super().__init__(*expressions, **extra)
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self.ordering = self._parse_expressions(*ordering)
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def resolve_expression(self, *args, **kwargs):
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self.ordering = [expr.resolve_expression(*args, **kwargs) for expr in self.ordering]
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return super().resolve_expression(*args, **kwargs)
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def as_sql(self, compiler, connection):
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if self.ordering:
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ordering_params = []
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ordering_expr_sql = []
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for expr in self.ordering:
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expr_sql, expr_params = expr.as_sql(compiler, connection)
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ordering_expr_sql.append(expr_sql)
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ordering_params.extend(expr_params)
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sql, sql_params = super().as_sql(compiler, connection, ordering=(
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'ORDER BY ' + ', '.join(ordering_expr_sql)
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))
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return sql, sql_params + ordering_params
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return super().as_sql(compiler, connection, ordering='')
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def set_source_expressions(self, exprs):
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# Extract the ordering expressions because ORDER BY clause is handled
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# in a custom way.
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self.ordering = exprs[self._get_ordering_expressions_index():]
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return super().set_source_expressions(exprs[:self._get_ordering_expressions_index()])
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def get_source_expressions(self):
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return super().get_source_expressions() + self.ordering
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def _get_ordering_expressions_index(self):
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"""Return the index at which the ordering expressions start."""
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source_expressions = self.get_source_expressions()
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return len(source_expressions) - len(self.ordering)
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