Support "blank" schema when MetaData.schema is set

Previously, it was impossible to have a Table that has
None for a schema name when the "schema" parameter on
MetaData was set.  A new symbol sqlalchemy.schema.BLANK_SCHEMA
is added which indicates that the schema name should unconditionally
be set to None.  In particular, this value must be passed within
cross-schema foreign key reflection, so that a Table which
is in the "default" schema can be represented properly.

Fixes: #3716
Change-Id: I3d24f99c22cded206c5379fd32a225e74edb7a8e

1 files changed, 25 insertions, 0 deletions

diff --git a/test/engine/test_reflection.py b/test/engine/test_reflection.py
index f9799fda0..0d98147cb 100644
--- a/test/engine/test_reflection.py
+++ b/test/engine/test_reflection.py
@@ -1304,6 +1304,31 @@ class SchemaTest(fixtures.TestBase):
             'sa_fake_schema_123'), False)
 
     @testing.requires.schemas
+    @testing.requires.cross_schema_fk_reflection
+    @testing.provide_metadata
+    def test_blank_schema_arg(self):
+        metadata = self.metadata
+
+        Table('some_table', metadata,
+              Column('id', Integer, primary_key=True),
+              Column('sid', Integer, sa.ForeignKey('some_other_table.id')),
+              schema=testing.config.test_schema
+              )
+        Table('some_other_table', metadata,
+              Column('id', Integer, primary_key=True),
+              schema=None
+              )
+        metadata.create_all()
+        with testing.db.connect() as conn:
+            meta2 = MetaData(conn, schema=testing.config.test_schema)
+            meta2.reflect()
+
+            eq_(set(meta2.tables), set(
+                [
+                    'some_other_table',
+                    '%s.some_table' % testing.config.test_schema]))
+
+    @testing.requires.schemas
     @testing.fails_on('sqlite', 'FIXME: unknown')
     @testing.fails_on('sybase', 'FIXME: unknown')
     def test_explicit_default_schema(self):