Render one CHECK for each StrEnum and Literal column

backend/druks/alembic_support.py

@@ -17,6 +17,10 @@ def _render_item(type_, obj, autogen_context):
         return "sa.String()"
     if type_ == "type" and isinstance(obj, EncryptedBytes | EncryptedJson | EncryptedText):
         return "sa.LargeBinary()"
+    # The column's type emits its own CHECK. SQLAlchemy 2.1 hides that from Alembic's
+    # own detection, so without this skip the revision renders the CHECK twice more.
+    if type_ == "check" and obj._type_bound:
+        return None
     return False
 
 

backend/tests/test_app_migrations.py

@@ -1,8 +1,13 @@
+import enum
 from pathlib import Path
+from typing import Literal
 from unittest.mock import MagicMock
 
 from alembic import command
+from alembic.autogenerate import render_python_code
 from alembic.config import Config
+from alembic.operations import ops
+from druks.alembic_support import _render_item
 from druks.database import make_app_migration
 from druks.files import File, FileField
 from druks.models import Base
@@ -24,6 +29,19 @@ class MigrationProbeFile(Base):
     image: Mapped[File] = FileField()
 
 
+class ChoiceProbeStatus(enum.StrEnum):
+    OPEN = "open"
+    CLOSED = "closed"
+
+
+class ChoiceProbe(Base):
+    __tablename__ = "choice_probe_rows"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    status: Mapped[ChoiceProbeStatus]
+    tone: Mapped[Literal["calm", "loud"]]
+
+
 _BASELINE = """\
 import sqlalchemy as sa
 from alembic import op
@@ -185,3 +203,9 @@ def test_file_field_autogenerates_and_upgrades_with_the_platform_foreign_key(
                 "DROP TABLE IF EXISTS migration_probe_files, alembic_version_migration_probe"
             )
         engine.dispose()
+
+
+def test_choice_columns_render_no_check_beside_their_type():
+    """A StrEnum or Literal column's type emits its own CHECK."""
+    upgrade = ops.UpgradeOps([ops.CreateTableOp.from_table(ChoiceProbe.__table__)])
+    assert "CheckConstraint" not in render_python_code(upgrade, render_item=_render_item)