- Added new generic function "next_value()", accepts

a Sequence object as its argument and renders the
appropriate "next value" generation string on the
target platform, if supported.  Also provides
".next_value()" method on Sequence itself.
[ticket:2085]
- added tests for all the conditions described
in [ticket:2085]
- postgresql dialect will exec/compile a Sequence
that has "optional=True".  the optional flag is now only
checked specifically in the context of a Table primary key
evaulation.
- func.next_value() or other SQL expression can
be embedded directly into an insert() construct,
and if implicit or explicit "returning" is used
in conjunction with a primary key column,
the newly generated value will be present in
result.inserted_primary_key. [ticket:2084]

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 9aed957d2..d49f12150 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -1178,14 +1178,16 @@ def _column_as_key(element):
     return element.key
 
 def _literal_as_text(element):
-    if hasattr(element, '__clause_element__'):
+    if isinstance(element, Visitable):
+        return element
+    elif hasattr(element, '__clause_element__'):
         return element.__clause_element__()
     elif isinstance(element, basestring):
         return _TextClause(unicode(element))
-    elif not isinstance(element, Visitable):
-        raise exc.ArgumentError("SQL expression object or string expected.")
     else:
-        return element
+        raise exc.ArgumentError(
+            "SQL expression object or string expected."
+        )
 
 def _clause_element_as_expr(element):
     if hasattr(element, '__clause_element__'):