remove comparsion in mapper._postfetch

heres the patch, which needs test coverage for its basic functionality (i.e. that all attributes are definitely populated), and also needs test coverage for the union against the "VALUES" list. a custom type with a broken comparator should be used in the tests to ensure that user-defined comparators are not involved at all. needs to be in 0.4 and 0.5.

Index: lib/sqlalchemy/orm/mapper.py
===================================================================
--- lib/sqlalchemy/orm/mapper.py    (revision 4563)
+++ lib/sqlalchemy/orm/mapper.py    (working copy)
@@ -1190,16 +1190,25 @@
         which will populate those attributes in one query when next accessed.
         """

-        postfetch_cols = util.Set(resultproxy.postfetch_cols()).union(util.Set(value_params.keys()))
-        deferred_props = [       # TODO: need test coverage for the "value_params" union here (nothing fails if you remove it)
+        # TODO: change resultproxy.post/prefetch_cols() to attributes
+        
+        postfetch_cols = util.Set(resultproxy.postfetch_cols()).union(value_params)  
+        generated_cols = util.Set(resultproxy.prefetch_cols())
+        
+        if self.polymorphic_on:
+            po = table.corresponding_column(self.polymorphic_on)
+            if po:
+                generated_cols.add(po)
+        if self.version_id_col:
+            generated_cols.add(self.version_id_col)

-        for c in self._cols_by_table[table](]
+):
-            if c in postfetch_cols and (not c.key in params or c in value_params):
-                prop = self._columntoproperty[c](c)
-                deferred_props.append(prop.key)
-            elif not c.primary_key and c.key in params and self._get_state_attr_by_column(state, c) != params[c.key](c.key):
+        for c in generated_cols:
+            if c.key in params:
                 self._set_state_attr_by_column(state, c, params[c.key](c.key))

+        deferred_props = [for prop in [self._columntoproperty[c](prop.key) for c in postfetch_cols]]
+
         if deferred_props:
             if self.eager_defaults:
                 _instance_key = self._identity_key_from_state(state)
Index: lib/sqlalchemy/engine/base.py
===================================================================
--- lib/sqlalchemy/engine/base.py   (revision 4563)
+++ lib/sqlalchemy/engine/base.py   (working copy)
@@ -1574,7 +1574,10 @@
         See ExecutionContext for details.
         """
         return self.context.postfetch_cols
-
+    
+    def prefetch_cols(self):
+        return self.context.prefetch_cols
+        
     def supports_sane_rowcount(self):
         """Return ``supports_sane_rowcount`` from the dialect.

Index: lib/sqlalchemy/engine/default.py
===================================================================
--- lib/sqlalchemy/engine/default.py    (revision 4563)
+++ lib/sqlalchemy/engine/default.py    (working copy)
@@ -395,3 +395,4 @@
                 self._last_updated_params = compiled_parameters

             self.postfetch_cols = self.compiled.postfetch
+            self.prefetch_cols = self.compiled.prefetch
\ No newline at end of file

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