Support state expiration for with_expression(); rename deferred_expression

The attributeimpl for a deferred_expression does not
support a scalar loader, add new configurability so that
the impl can have this flag turned off.   Document
that the with_expression() system currently does not
offer any deferred loading.

To eliminate confusion over "deferred", which refers to
lazy loading of column attributes, and "with_expression",
which refers to an attribute that is explicitly at
query time only, rename deferred_expression to query_expression.

Change-Id: I07c4a050ed68c79ccbde9492e9de1630b7470d74

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 4e7636cf8..4b9eb3b0f 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -195,7 +195,7 @@ class ColumnLoader(LoaderStrategy):
 
 
 @log.class_logger
-@properties.ColumnProperty.strategy_for(deferred_expression=True)
+@properties.ColumnProperty.strategy_for(query_expression=True)
 class ExpressionColumnLoader(ColumnLoader):
     def __init__(self, parent, strategy_key):
         super(ExpressionColumnLoader, self).__init__(parent, strategy_key)
@@ -235,6 +235,15 @@ class ExpressionColumnLoader(ColumnLoader):
             else:
                 populators["expire"].append((self.key, True))
 
+    def init_class_attribute(self, mapper):
+        self.is_class_level = True
+
+        _register_attribute(
+            self.parent_property, mapper, useobject=False,
+            compare_function=self.columns[0].type.compare_values,
+            accepts_scalar_loader=False
+        )
+
 
 @log.class_logger
 @properties.ColumnProperty.strategy_for(deferred=True, instrument=True)