Fix upsert with limited number of columns (#58)

pg.py

@@ -2476,7 +2476,7 @@ def upsert(self, table, row=None, **kw):
         keyname.add('oid')
         for n in attnames:
             if n not in keyname:
-                value = kw.get(n, True)
+                value = kw.get(n, n in row)
                 if value:
                     if not isinstance(value, basestring):
                         value = 'excluded.%s' % col(n)

tests/test_classic_dbwrapper.py

@@ -2160,6 +2160,12 @@ def testUpsert(self):
         s = dict(m=3, u='z')
         r = upsert(table, s, oid='invalid')
         self.assertIs(r, s)
+        s = dict(n=2)
+        # do not modify columns missing in the dict
+        r = upsert(table, s)
+        self.assertIs(r, s)
+        r = query(q).getresult()
+        self.assertEqual(r, [(1, 'x2'), (2, 'y3')])
 
     def testUpsertWithOids(self):
         if not self.oids: