Fix db_default on FK/O2O dropped during _init_relations (#2200)

Author: mixartemev

CHANGELOG.rst

@@ -21,6 +21,7 @@ Added
 Fixed
 ^^^^^
 - ``MigrationRecorder`` now uses parameterized queries; fixes MariaDB/MySQL rejecting ISO-8601 ``applied_at`` values. (#2132)
+- ``db_default`` on ``ForeignKeyField``/``OneToOneField`` now propagates to the underlying ``<fk>_id`` column, so ``CREATE TABLE`` emits the ``DEFAULT`` clause for FK columns. (#2199)
 - ``MigrationRecorder`` no longer emits tortoise's own ``pk`` field ``DeprecationWarning`` when applying migrations; it now builds its bookkeeping model with ``primary_key=True``. (#2203)
 - ``QuerySet.count()`` now matches the limited query result for the LIMIT/OFFSET edge cases: it returns ``0`` (instead of a negative number) when ``offset()`` exceeds the total row count, and ``0`` (instead of the total) for ``limit(0)``. (#2208)
 - Field declarations on models now resolve to their concrete type (e.g. ``CharField[str]``) in Pyright/Pylance instead of ``Field[Unknown]``; the ``Field.__new__`` type-check stub now returns ``Self``. (#2216)

tests/migrations/test_schema_editor_sql.py

@@ -249,3 +249,36 @@ class Meta:
     sql = client.executed[0]
     assert 'CREATE TABLE "widget"' in sql
     assert "DEFAULT 'active'" in sql
+
+
+@pytest.mark.asyncio
+async def test_create_model_includes_db_default_on_fk() -> None:
+    """CreateModel should include DEFAULT clause for FK columns with db_default."""
+
+    class Dc(Model):
+        id = fields.IntField(primary_key=True)
+
+        class Meta:
+            table = "dc"
+            app = "models"
+
+    class App(Model):
+        id = fields.IntField(primary_key=True)
+        dc: fields.ForeignKeyRelation[Dc] = fields.ForeignKeyField("models.Dc", db_default=2)
+
+        class Meta:
+            table = "app"
+            app = "models"
+
+    init_apps(Dc, App)
+
+    client = FakeClient("sql")
+    editor = TestSchemaEditor(client)
+
+    await editor.create_model(App)
+
+    assert len(client.executed) == 1
+    sql = client.executed[0]
+    assert 'CREATE TABLE "app"' in sql
+    assert '"dc_id"' in sql
+    assert "DEFAULT 2" in sql

tortoise/apps.py

@@ -192,7 +192,7 @@ def init_fk_o2o_field(model: type[Model], field: str, is_o2o: bool = False) -> N
             key_field = f"{field}_id"
             key_fk_object.reference = fk_object
             key_fk_object.source_field = fk_object.source_field or key_field
-            for attr in ("index", "default", "null", "generated", "description"):
+            for attr in ("index", "default", "null", "generated", "description", "db_default"):
                 setattr(key_fk_object, attr, getattr(fk_object, attr))
             if is_o2o:
                 key_fk_object.pk = fk_object.pk