- exists() becomes useable as a standalone selectable, not just in a

WHERE clause

3 files changed, 17 insertions, 4 deletions

diff --git a/CHANGES b/CHANGES
index 921c06a41..8602e82db 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+- sql:
+    - exists() becomes useable as a standalone selectable, not just in a 
+    WHERE clause
 - orm:
     - a full select() construct can be passed to query.select() (which
       worked anyway), but also query.selectfirst(), query.selectone() which
diff --git a/lib/sqlalchemy/sql.py b/lib/sqlalchemy/sql.py
index 275fec343..3acd76258 100644
--- a/lib/sqlalchemy/sql.py
+++ b/lib/sqlalchemy/sql.py
@@ -170,11 +170,10 @@ def extract(field, expr):
     """return extract(field FROM expr)"""
     expr = _BinaryClause(text(field), expr, "FROM")
     return func.extract(expr)
+
     
-def exists(*args, **params):
-    params['correlate'] = True
-    s = select(*args, **params)
-    return _BooleanExpression(_TextClause("EXISTS"), s, None)
+def exists(*args, **kwargs):
+    return _Exists(*args, **kwargs)
 
 def union(*selects, **params):
     return _compound_select('UNION', *selects, **params)
@@ -1118,6 +1117,14 @@ class _BooleanExpression(_BinaryExpression):
             return _BooleanExpression(self.left, self.right, self.negate, negate=self.operator, type=self.type)
         else:
             return super(_BooleanExpression, self)._negate()
+
+class _Exists(_BooleanExpression):
+    def __init__(self, *args, **kwargs):
+        kwargs['correlate'] = True
+        s = select(*args, **kwargs)
+        _BooleanExpression.__init__(self, _TextClause("EXISTS"), s, None)
+    def _hide_froms(self):
+        return self._get_from_objects()
         
 class Join(FromClause):
     def __init__(self, left, right, onclause=None, isouter = False):
diff --git a/test/sql/select.py b/test/sql/select.py
index bdc79c400..7473d4f63 100644
--- a/test/sql/select.py
+++ b/test/sql/select.py
@@ -124,6 +124,9 @@ sq.myothertable_othername AS sq_myothertable_othername FROM (" + sqstring + ") A
     
     def testdontovercorrelate(self):
         self.runtest(select([table1], from_obj=[table1, table1.select()]), """SELECT mytable.myid, mytable.name, mytable.description FROM mytable, (SELECT mytable.myid AS myid, mytable.name AS name, mytable.description AS description FROM mytable)""")
+    
+    def testselectexists(self):
+        self.runtest(exists([table1.c.myid], table1.c.myid==5).select(), "SELECT EXISTS (SELECT mytable.myid AS myid FROM mytable WHERE mytable.myid = :mytable_myid)", params={'mytable_myid':5})
         
     def testwheresubquery(self):
         # TODO: this tests that you dont get a "SELECT column" without a FROM but its not working yet.