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Diffstat (limited to 'lib/sqlalchemy/sql/default_comparator.py')
| -rw-r--r-- | lib/sqlalchemy/sql/default_comparator.py | 278 |
1 files changed, 278 insertions, 0 deletions
diff --git a/lib/sqlalchemy/sql/default_comparator.py b/lib/sqlalchemy/sql/default_comparator.py new file mode 100644 index 000000000..c39dce9c6 --- /dev/null +++ b/lib/sqlalchemy/sql/default_comparator.py @@ -0,0 +1,278 @@ +# sql/default_comparator.py +# Copyright (C) 2005-2014 the SQLAlchemy authors and contributors <see AUTHORS file> +# +# This module is part of SQLAlchemy and is released under +# the MIT License: http://www.opensource.org/licenses/mit-license.php + +"""Default implementation of SQL comparison operations. +""" + +from .. import exc, util +from . import operators +from . import type_api +from .elements import BindParameter, True_, False_, BinaryExpression, \ + Null, _const_expr, _clause_element_as_expr, \ + ClauseList, ColumnElement, TextClause, UnaryExpression, \ + collate, _is_literal, _literal_as_text +from .selectable import SelectBase, Alias, Selectable, ScalarSelect + +class _DefaultColumnComparator(operators.ColumnOperators): + """Defines comparison and math operations. + + See :class:`.ColumnOperators` and :class:`.Operators` for descriptions + of all operations. + + """ + + @util.memoized_property + def type(self): + return self.expr.type + + def operate(self, op, *other, **kwargs): + o = self.operators[op.__name__] + return o[0](self, self.expr, op, *(other + o[1:]), **kwargs) + + def reverse_operate(self, op, other, **kwargs): + o = self.operators[op.__name__] + return o[0](self, self.expr, op, other, reverse=True, *o[1:], **kwargs) + + def _adapt_expression(self, op, other_comparator): + """evaluate the return type of <self> <op> <othertype>, + and apply any adaptations to the given operator. + + This method determines the type of a resulting binary expression + given two source types and an operator. For example, two + :class:`.Column` objects, both of the type :class:`.Integer`, will + produce a :class:`.BinaryExpression` that also has the type + :class:`.Integer` when compared via the addition (``+``) operator. + However, using the addition operator with an :class:`.Integer` + and a :class:`.Date` object will produce a :class:`.Date`, assuming + "days delta" behavior by the database (in reality, most databases + other than Postgresql don't accept this particular operation). + + The method returns a tuple of the form <operator>, <type>. + The resulting operator and type will be those applied to the + resulting :class:`.BinaryExpression` as the final operator and the + right-hand side of the expression. + + Note that only a subset of operators make usage of + :meth:`._adapt_expression`, + including math operators and user-defined operators, but not + boolean comparison or special SQL keywords like MATCH or BETWEEN. + + """ + return op, other_comparator.type + + def _boolean_compare(self, expr, op, obj, negate=None, reverse=False, + _python_is_types=(util.NoneType, bool), + **kwargs): + + if isinstance(obj, _python_is_types + (Null, True_, False_)): + + # allow x ==/!= True/False to be treated as a literal. + # this comes out to "== / != true/false" or "1/0" if those + # constants aren't supported and works on all platforms + if op in (operators.eq, operators.ne) and \ + isinstance(obj, (bool, True_, False_)): + return BinaryExpression(expr, + _literal_as_text(obj), + op, + type_=type_api.BOOLEANTYPE, + negate=negate, modifiers=kwargs) + else: + # all other None/True/False uses IS, IS NOT + if op in (operators.eq, operators.is_): + return BinaryExpression(expr, _const_expr(obj), + operators.is_, + negate=operators.isnot) + elif op in (operators.ne, operators.isnot): + return BinaryExpression(expr, _const_expr(obj), + operators.isnot, + negate=operators.is_) + else: + raise exc.ArgumentError( + "Only '=', '!=', 'is_()', 'isnot()' operators can " + "be used with None/True/False") + else: + obj = self._check_literal(expr, op, obj) + + if reverse: + return BinaryExpression(obj, + expr, + op, + type_=type_api.BOOLEANTYPE, + negate=negate, modifiers=kwargs) + else: + return BinaryExpression(expr, + obj, + op, + type_=type_api.BOOLEANTYPE, + negate=negate, modifiers=kwargs) + + def _binary_operate(self, expr, op, obj, reverse=False, result_type=None, + **kw): + obj = self._check_literal(expr, op, obj) + + if reverse: + left, right = obj, expr + else: + left, right = expr, obj + + if result_type is None: + op, result_type = left.comparator._adapt_expression( + op, right.comparator) + + return BinaryExpression(left, right, op, type_=result_type) + + def _scalar(self, expr, op, fn, **kw): + return fn(expr) + + def _in_impl(self, expr, op, seq_or_selectable, negate_op, **kw): + seq_or_selectable = _clause_element_as_expr(seq_or_selectable) + + if isinstance(seq_or_selectable, ScalarSelect): + return self._boolean_compare(expr, op, seq_or_selectable, + negate=negate_op) + elif isinstance(seq_or_selectable, SelectBase): + + # TODO: if we ever want to support (x, y, z) IN (select x, + # y, z from table), we would need a multi-column version of + # as_scalar() to produce a multi- column selectable that + # does not export itself as a FROM clause + + return self._boolean_compare( + expr, op, seq_or_selectable.as_scalar(), + negate=negate_op, **kw) + elif isinstance(seq_or_selectable, (Selectable, TextClause)): + return self._boolean_compare(expr, op, seq_or_selectable, + negate=negate_op, **kw) + + # Handle non selectable arguments as sequences + args = [] + for o in seq_or_selectable: + if not _is_literal(o): + if not isinstance(o, operators.ColumnOperators): + raise exc.InvalidRequestError('in() function accept' + 's either a list of non-selectable values, ' + 'or a selectable: %r' % o) + elif o is None: + o = Null() + else: + o = expr._bind_param(op, o) + args.append(o) + if len(args) == 0: + + # Special case handling for empty IN's, behave like + # comparison against zero row selectable. We use != to + # build the contradiction as it handles NULL values + # appropriately, i.e. "not (x IN ())" should not return NULL + # values for x. + + util.warn('The IN-predicate on "%s" was invoked with an ' + 'empty sequence. This results in a ' + 'contradiction, which nonetheless can be ' + 'expensive to evaluate. Consider alternative ' + 'strategies for improved performance.' % expr) + if op is operators.in_op: + return expr != expr + else: + return expr == expr + + return self._boolean_compare(expr, op, + ClauseList(*args).self_group(against=op), + negate=negate_op) + + def _unsupported_impl(self, expr, op, *arg, **kw): + raise NotImplementedError("Operator '%s' is not supported on " + "this expression" % op.__name__) + + def _neg_impl(self, expr, op, **kw): + """See :meth:`.ColumnOperators.__neg__`.""" + return UnaryExpression(expr, operator=operators.neg) + + def _match_impl(self, expr, op, other, **kw): + """See :meth:`.ColumnOperators.match`.""" + return self._boolean_compare(expr, operators.match_op, + self._check_literal(expr, operators.match_op, + other)) + + def _distinct_impl(self, expr, op, **kw): + """See :meth:`.ColumnOperators.distinct`.""" + return UnaryExpression(expr, operator=operators.distinct_op, + type_=expr.type) + + def _between_impl(self, expr, op, cleft, cright, **kw): + """See :meth:`.ColumnOperators.between`.""" + return BinaryExpression( + expr, + ClauseList( + self._check_literal(expr, operators.and_, cleft), + self._check_literal(expr, operators.and_, cright), + operator=operators.and_, + group=False, group_contents=False), + operators.between_op) + + def _collate_impl(self, expr, op, other, **kw): + return collate(expr, other) + + # a mapping of operators with the method they use, along with + # their negated operator for comparison operators + operators = { + "add": (_binary_operate,), + "mul": (_binary_operate,), + "sub": (_binary_operate,), + "div": (_binary_operate,), + "mod": (_binary_operate,), + "truediv": (_binary_operate,), + "custom_op": (_binary_operate,), + "concat_op": (_binary_operate,), + "lt": (_boolean_compare, operators.ge), + "le": (_boolean_compare, operators.gt), + "ne": (_boolean_compare, operators.eq), + "gt": (_boolean_compare, operators.le), + "ge": (_boolean_compare, operators.lt), + "eq": (_boolean_compare, operators.ne), + "like_op": (_boolean_compare, operators.notlike_op), + "ilike_op": (_boolean_compare, operators.notilike_op), + "notlike_op": (_boolean_compare, operators.like_op), + "notilike_op": (_boolean_compare, operators.ilike_op), + "contains_op": (_boolean_compare, operators.notcontains_op), + "startswith_op": (_boolean_compare, operators.notstartswith_op), + "endswith_op": (_boolean_compare, operators.notendswith_op), + "desc_op": (_scalar, UnaryExpression._create_desc), + "asc_op": (_scalar, UnaryExpression._create_asc), + "nullsfirst_op": (_scalar, UnaryExpression._create_nullsfirst), + "nullslast_op": (_scalar, UnaryExpression._create_nullslast), + "in_op": (_in_impl, operators.notin_op), + "notin_op": (_in_impl, operators.in_op), + "is_": (_boolean_compare, operators.is_), + "isnot": (_boolean_compare, operators.isnot), + "collate": (_collate_impl,), + "match_op": (_match_impl,), + "distinct_op": (_distinct_impl,), + "between_op": (_between_impl, ), + "neg": (_neg_impl,), + "getitem": (_unsupported_impl,), + "lshift": (_unsupported_impl,), + "rshift": (_unsupported_impl,), + } + + def _check_literal(self, expr, operator, other): + if isinstance(other, (ColumnElement, TextClause)): + if isinstance(other, BindParameter) and \ + other.type._isnull: + other = other._clone() + other.type = expr.type + return other + elif hasattr(other, '__clause_element__'): + other = other.__clause_element__() + elif isinstance(other, type_api.TypeEngine.Comparator): + other = other.expr + + if isinstance(other, (SelectBase, Alias)): + return other.as_scalar() + elif not isinstance(other, (ColumnElement, TextClause)): + return expr._bind_param(operator, other) + else: + return other + |