From 69dcd805d2c6ed92adf81da443c5c06d23d3423a Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Sun, 17 Apr 2011 15:37:12 -0400
Subject: - Added explicit true()/false() constructs to expression lib -
 coercion rules will intercept "False"/"True" into these constructs.  In 0.6,
 the constructs were typically converted straight to string, which was no
 longer accepted in 0.7.  [ticket:2117]

---
 lib/sqlalchemy/sql/expression.py | 54 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 3 deletions(-)

(limited to 'lib/sqlalchemy/sql/expression.py')

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index b7e543850..c552f055f 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -1046,12 +1046,25 @@ def over(func, partition_by=None, order_by=None):
     return _Over(func, partition_by=partition_by, order_by=order_by)
 
 def null():
-    """Return a :class:`_Null` object, which compiles to ``NULL`` in a sql
-    statement.
+    """Return a :class:`_Null` object, which compiles to ``NULL``.
 
     """
     return _Null()
 
+def true():
+    """Return a :class:`_True` object, which compiles to ``true``, or the 
+    boolean equivalent for the target dialect.
+
+    """
+    return _True()
+
+def false():
+    """Return a :class:`_False` object, which compiles to ``false``, or the 
+    boolean equivalent for the target dialect.
+
+    """
+    return _False()
+
 class _FunctionGenerator(object):
     """Generate :class:`.Function` objects based on getattr calls."""
 
@@ -1199,11 +1212,25 @@ def _literal_as_text(element):
         return element.__clause_element__()
     elif isinstance(element, basestring):
         return _TextClause(unicode(element))
+    elif isinstance(element, (util.NoneType, bool)):
+        return _const_expr(element)
     else:
         raise exc.ArgumentError(
             "SQL expression object or string expected."
         )
 
+def _const_expr(element):
+    if element is None:
+        return null()
+    elif element is False:
+        return false()
+    elif element is True:
+        return true()
+    else:
+        raise exc.ArgumentError(
+            "Expected None, False, or True"
+        )
+
 def _clause_element_as_expr(element):
     if hasattr(element, '__clause_element__'):
         return element.__clause_element__()
@@ -2840,10 +2867,31 @@ class _Null(ColumnElement):
     """
 
     __visit_name__ = 'null'
-
     def __init__(self):
         self.type = sqltypes.NULLTYPE
 
+class _False(ColumnElement):
+    """Represent the ``false`` keyword in a SQL statement.
+
+    Public constructor is the :func:`false()` function.
+
+    """
+
+    __visit_name__ = 'false'
+    def __init__(self):
+        self.type = sqltypes.BOOLEANTYPE
+
+class _True(ColumnElement):
+    """Represent the ``true`` keyword in a SQL statement.
+
+    Public constructor is the :func:`true()` function.
+
+    """
+
+    __visit_name__ = 'true'
+    def __init__(self):
+        self.type = sqltypes.BOOLEANTYPE
+
 
 class ClauseList(ClauseElement):
     """Describe a list of clauses, separated by an operator.
-- 
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