diff options
Diffstat (limited to 'lib/sqlalchemy/sql/expression.py')
| -rw-r--r-- | lib/sqlalchemy/sql/expression.py | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py index 903b3052d..f94e849e5 100644 --- a/lib/sqlalchemy/sql/expression.py +++ b/lib/sqlalchemy/sql/expression.py @@ -1527,7 +1527,7 @@ class _CompareMixin(ColumnOperators): return other.__clause_element__() elif not isinstance(other, ClauseElement): return self._bind_param(other) - elif isinstance(other, _SelectBaseMixin): + elif isinstance(other, (_SelectBaseMixin, Alias)): return other.as_scalar() else: return other @@ -1769,7 +1769,21 @@ class FromClause(Selectable): return Join(self, right, onclause, True) def alias(self, name=None): - """return an alias of this ``FromClause`` against another ``FromClause``.""" + """return an alias of this ``FromClause``. + + For table objects, this has the effect of the table being rendered + as ``tablename AS aliasname`` in a SELECT statement. + For select objects, the effect is that of creating a named + subquery, i.e. ``(select ...) AS aliasname``. + The ``alias()`` method is the general way to create + a "subquery" out of an existing SELECT. + + The ``name`` parameter is optional, and if left blank an + "anonymous" name will be generated at compile time, guaranteed + to be unique against other anonymous constructs used in the + same statement. + + """ return Alias(self, name) @@ -2600,6 +2614,12 @@ class Alias(FromClause): def description(self): return self.name.encode('ascii', 'backslashreplace') + def as_scalar(self): + try: + return self.element.as_scalar() + except AttributeError: + raise AttributeError("Element %s does not support 'as_scalar()'" % self.element) + def is_derived_from(self, fromclause): if fromclause in self._cloned_set: return True |