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

3 files changed, 52 insertions, 1 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
 
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):
diff --git a/test/sql/test_metadata.py b/test/sql/test_metadata.py
index 050929d3d..449956fcd 100644
--- a/test/sql/test_metadata.py
+++ b/test/sql/test_metadata.py
@@ -7,7 +7,8 @@ from sqlalchemy import Integer, String, UniqueConstraint, \
     CheckConstraint, ForeignKey, MetaData, Sequence, \
     ForeignKeyConstraint, PrimaryKeyConstraint, ColumnDefault, Index, event,\
     events, Unicode, types as sqltypes, bindparam, \
-    Table, Column, Boolean, Enum, func, text, TypeDecorator
+    Table, Column, Boolean, Enum, func, text, TypeDecorator, \
+    BLANK_SCHEMA
 from sqlalchemy import schema, exc
 from sqlalchemy.engine import default
 from sqlalchemy.sql import elements, naming
@@ -446,6 +447,7 @@ class MetaDataTest(fixtures.TestBase, ComparesTables):
                     ('t2', m1, 'sch2', None, 'sch2', None),
                     ('t3', m1, 'sch2', True, 'sch2', True),
                     ('t4', m1, 'sch1', None, 'sch1', None),
+                    ('t5', m1, BLANK_SCHEMA, None, None, None),
                     ('t1', m2, None, None, 'sch1', True),
                     ('t2', m2, 'sch2', None, 'sch2', None),
                     ('t3', m2, 'sch2', True, 'sch2', True),
@@ -458,6 +460,7 @@ class MetaDataTest(fixtures.TestBase, ComparesTables):
                     ('t2', m4, 'sch2', None, 'sch2', None),
                     ('t3', m4, 'sch2', True, 'sch2', True),
                     ('t4', m4, 'sch1', None, 'sch1', None),
+                    ('t5', m4, BLANK_SCHEMA, None, None, None),
                 ]):
             kw = {}
             if schema is not None: