Allow Table._reset_exported to silently pass

Fixed bug in :class:`.Table` where the internal method
``_reset_exported()`` would corrupt the state of the object.  This
method is intended for selectable objects and is called by the ORM
in some cases; an erroneous mapper configuration would could lead the
ORM to call this on on a :class:`.Table` object.

Change-Id: I63fa34ee0cdf16358bb125c556390df79758bcbc
Fixes: #3755

4 files changed, 28 insertions, 2 deletions

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index c977c7366..16a38e662 100644
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -19,6 +19,16 @@
     :version: 1.0.15
 
     .. change::
+        :tags: bug, sql
+        :tickets: 3755
+
+        Fixed bug in :class:`.Table` where the internal method
+        ``_reset_exported()`` would corrupt the state of the object.  This
+        method is intended for selectable objects and is called by the ORM
+        in some cases; an erroneous mapper configuration would could lead the
+        ORM to call this on on a :class:`.Table` object.
+
+    .. change::
         :tags: bug, ext
         :tickets: 3743
 
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 858c35344..b76a6f727 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1230,7 +1230,6 @@ class Mapper(InspectionAttr):
             instrumentation.unregister_class(self.class_)
 
     def _configure_pks(self):
-
         self.tables = sql_util.find_tables(self.mapped_table)
 
         self._pks_by_table = {}
@@ -1316,7 +1315,6 @@ class Mapper(InspectionAttr):
                 col.table not in self._cols_by_table))
 
     def _configure_properties(self):
-
         # Column and other ClauseElement objects which are mapped
         self.columns = self.c = util.OrderedProperties()
 
diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index ee139827a..55d0b74e6 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -598,6 +598,9 @@ class Table(DialectKWArgs, SchemaItem, TableClause):
     def _init_collections(self):
         pass
 
+    def _reset_exported(self):
+        pass
+
     @property
     def _autoincrement_column(self):
         return self.primary_key._autoincrement_column
diff --git a/test/sql/test_metadata.py b/test/sql/test_metadata.py
index 92d35e6e5..846e70589 100644
--- a/test/sql/test_metadata.py
+++ b/test/sql/test_metadata.py
@@ -1231,6 +1231,21 @@ class TableTest(fixtures.TestBase, AssertsCompiledSQL):
             t.info['bar'] = 'zip'
             assert t.info['bar'] == 'zip'
 
+    def test_reset_exported_passes(self):
+
+        m = MetaData()
+
+        t = Table('t', m, Column('foo', Integer))
+        eq_(
+            list(t.c), [t.c.foo]
+        )
+
+        t._reset_exported()
+
+        eq_(
+            list(t.c), [t.c.foo]
+        )
+
     def test_foreign_key_constraints_collection(self):
         metadata = MetaData()
         t1 = Table('foo', metadata, Column('a', Integer))