``Identity`` implies ``nullable=False``.

Altered the behavior of the :class:`_schema.Identity` construct such that
when applied to a :class:`_schema.Column`, it will automatically imply that
the value of :paramref:`_sql.Column.nullable` should default to ``False``,
in a similar manner as when the :paramref:`_sql.Column.primary_key`
parameter is set to ``True``.   This matches the default behavior of all
supporting databases where ``IDENTITY`` implies ``NOT NULL``.  The
PostgreSQL backend is the only one that supports adding ``NULL`` to an
``IDENTITY`` column, which is here supported by passing a ``True`` value
for the :paramref:`_sql.Column.nullable` parameter at the same time.

Fixes: #5775
Change-Id: I0516d506ff327cff35cda605e8897a27440e0373

1 files changed, 19 insertions, 0 deletions

diff --git a/test/dialect/postgresql/test_compiler.py b/test/dialect/postgresql/test_compiler.py
index b3a0b9bbd..ec165960f 100644
--- a/test/dialect/postgresql/test_compiler.py
+++ b/test/dialect/postgresql/test_compiler.py
@@ -1778,6 +1778,25 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "(INCREMENT BY 7 START WITH 4))",
         )
 
+    def test_column_identity_null(self):
+        # all other tests are in test_identity_column.py
+        m = MetaData()
+        t = Table(
+            "t",
+            m,
+            Column(
+                "y",
+                Integer,
+                Identity(always=True, start=4, increment=7),
+                nullable=True,
+            ),
+        )
+        self.assert_compile(
+            schema.CreateTable(t),
+            "CREATE TABLE t (y INTEGER GENERATED ALWAYS AS IDENTITY "
+            "(INCREMENT BY 7 START WITH 4) NULL)",
+        )
+
     def test_index_extra_include_1(self):
         metadata = MetaData()
         tbl = Table(