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, 23 insertions, 0 deletions

diff --git a/test/dialect/postgresql/test_reflection.py b/test/dialect/postgresql/test_reflection.py
index 8da18108f..4897c4a7e 100644
--- a/test/dialect/postgresql/test_reflection.py
+++ b/test/dialect/postgresql/test_reflection.py
@@ -582,6 +582,29 @@ class ReflectionTest(fixtures.TestBase):
                 ['test_schema_2.some_other_table', 'test_schema.some_table']))
 
     @testing.provide_metadata
+    def test_cross_schema_reflection_metadata_uses_schema(self):
+        # test [ticket:3716]
+
+        metadata = self.metadata
+
+        Table('some_table', metadata,
+              Column('id', Integer, primary_key=True),
+              Column('sid', Integer, ForeignKey('some_other_table.id')),
+              schema='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="test_schema")
+            meta2.reflect()
+
+            eq_(set(meta2.tables), set(
+                ['some_other_table', 'test_schema.some_table']))
+
+    @testing.provide_metadata
     def test_uppercase_lowercase_table(self):
         metadata = self.metadata