support BLANK_SCHEMA, RETAIN_SCHEMA FK schema on copy

Added support so that the :paramref:`.Table.tometadata.referred_schema_fn`
callable passed to :meth:`.Table.to_metadata` may return the value
:data:`.BLANK_SCHEMA` to indicate that the referenced foreign key should be
reset to None. The :data.`RETAIN_SCHEMA` symbol may also be returned from
this function to indicate "no change", which will behave the same as
``None`` currently does which also indicates no change.

Fixes: #7860
Change-Id: I82a45988d534295d8356453f68001b21d4ff706d

1 files changed, 22 insertions, 0 deletions

diff --git a/test/sql/test_metadata.py b/test/sql/test_metadata.py
index 21fc0a627..f7480d11a 100644
--- a/test/sql/test_metadata.py
+++ b/test/sql/test_metadata.py
@@ -41,6 +41,7 @@ from sqlalchemy.sql import naming
 from sqlalchemy.sql import operators
 from sqlalchemy.sql.elements import _NONE_NAME
 from sqlalchemy.sql.elements import literal_column
+from sqlalchemy.sql.schema import RETAIN_SCHEMA
 from sqlalchemy.testing import assert_raises
 from sqlalchemy.testing import assert_raises_message
 from sqlalchemy.testing import AssertsCompiledSQL
@@ -1315,6 +1316,27 @@ class ToMetaDataTest(fixtures.TestBase, AssertsCompiledSQL, ComparesTables):
 
         self._assert_fk(t2, "z", "h.t1.x", referred_schema_fn=ref_fn)
 
+    def test_fk_reset_to_none(self):
+        m = MetaData()
+
+        t2 = Table("t2", m, Column("y", Integer, ForeignKey("p.t1.x")))
+
+        def ref_fn(table, to_schema, constraint, referred_schema):
+            return BLANK_SCHEMA
+
+        self._assert_fk(t2, None, "t1.x", referred_schema_fn=ref_fn)
+
+    @testing.combinations(None, RETAIN_SCHEMA)
+    def test_fk_test_non_return_for_referred_schema(self, sym):
+        m = MetaData()
+
+        t2 = Table("t2", m, Column("y", Integer, ForeignKey("p.t1.x")))
+
+        def ref_fn(table, to_schema, constraint, referred_schema):
+            return sym
+
+        self._assert_fk(t2, None, "p.t1.x", referred_schema_fn=ref_fn)
+
     def test_copy_info(self):
         m = MetaData()
         fk = ForeignKey("t2.id")