Require a database for Django to start (#42)

paas_app_charmer/django/charm.py

@@ -71,6 +71,29 @@ def get_cos_dir(self) -> str:
         """
         return str((pathlib.Path(__file__).parent / "cos").absolute())
 
+    def is_ready(self) -> bool:
+        """Check if the charm is ready to start the workload application.
+
+        For Django, at least one database is needed. Migrations will be run on startup
+        and without that integration it will fail.
+
+        Returns:
+            True if the charm is ready to start the workload application.
+        """
+        if not super().is_ready():
+            return False
+
+        # At this point all integrations are correctly configured. If there is no database uri,
+        # it means that there is no integration for databases or they are optional and no one
+        # is set.
+        charm_state = self._create_charm_state()
+        if not charm_state.integrations.databases_uris:
+            self.update_app_and_unit_status(
+                ops.BlockedStatus("Django requires a database integration to work")
+            )
+            return False
+        return True
+
     def _on_create_superuser_action(self, event: ops.ActionEvent) -> None:
         """Handle the create-superuser action.
 

tests/unit/django/conftest.py

@@ -5,6 +5,7 @@
 import os
 import pathlib
 import shlex
+import textwrap
 import typing
 import unittest.mock
 
@@ -28,7 +29,67 @@ def cwd():
 @pytest.fixture(name="harness")
 def harness_fixture() -> typing.Generator[Harness, None, None]:
     """Ops testing framework harness fixture."""
-    harness = Harness(DjangoCharm)
+    harness = _build_harness()
+    yield harness
+    harness.cleanup()
+
+
+@pytest.fixture(name="harness_no_integrations")
+def harness_no_integrations_fixture() -> typing.Generator[Harness, None, None]:
+    """Ops testing framework harness fixture without a database."""
+    meta = textwrap.dedent(
+        """
+    name: django-k8s
+
+    bases:
+      - build-on:
+          - name: ubuntu
+            channel: "22.04"
+        run-on:
+          - name: ubuntu
+            channel: "22.04"
+
+    summary: An example Django application.
+
+    description: An example Django application.
+
+    containers:
+      django-app:
+        resource: django-app-image
+
+    peers:
+      secret-storage:
+        interface: secret-storage
+    provides:
+      grafana-dashboard:
+        interface: grafana_dashboard
+      metrics-endpoint:
+        interface: prometheus_scrape
+    requires:
+      ingress:
+        interface: ingress
+        limit: 1
+      logging:
+        interface: loki_push_api
+    """
+    )
+    harness = _build_harness(meta)
+    yield harness
+    harness.cleanup()
+
+
+@pytest.fixture
+def database_migration_mock():
+    """Create a mock instance for the DatabaseMigration class."""
+    mock = unittest.mock.MagicMock()
+    mock.status = DatabaseMigrationStatus.PENDING
+    mock.script = None
+    return mock
+
+
+def _build_harness(meta=None):
+    """Create a harness instance with the specified metadata."""
+    harness = Harness(DjangoCharm, meta=meta)
     harness.set_leader()
     container = "django-app"
     root = harness.get_filesystem_root(container)
@@ -51,15 +112,4 @@ def check_config_handler(_):
         check_config_command,
         handler=check_config_handler,
     )
-
-    yield harness
-    harness.cleanup()
-
-
-@pytest.fixture
-def database_migration_mock():
-    """Create a mock instance for the DatabaseMigration class."""
-    mock = unittest.mock.MagicMock()
-    mock.status = DatabaseMigrationStatus.PENDING
-    mock.script = None
-    return mock
+    return harness

tests/unit/django/test_charm.py

@@ -1,16 +1,18 @@
 # Copyright 2024 Canonical Ltd.
 # See LICENSE file for licensing details.
 
-"""Flask charm unit tests."""
+"""Django charm unit tests."""
 
 # this is a unit test file
 # pylint: disable=protected-access
 
 import unittest.mock
 
+import ops
 import pytest
 from ops.testing import ExecArgs, ExecResult, Harness
 
+from examples.django.charm.src.charm import DjangoCharm
 from paas_app_charmer._gunicorn.webserver import GunicornWebserver, WebserverConfig
 from paas_app_charmer._gunicorn.workload_config import create_workload_config
 from paas_app_charmer._gunicorn.wsgi_app import WsgiApp
@@ -43,7 +45,7 @@ def test_django_config(harness: Harness, config: dict, env: dict) -> None:
     """
     arrange: none
     act: start the django charm and set django-app container to be ready.
-    assert: flask charm should submit the correct flaks pebble layer to pebble.
+    assert: django charm should submit the correct pebble layer to pebble.
     """
     harness.begin()
     container = harness.charm.unit.get_container("django-app")
@@ -124,3 +126,19 @@ def handler(args: ExecArgs) -> None | ExecResult:
     )
     assert "password" in output.results
     assert output.results["password"] == password
+
+
+def test_required_database_integration(harness_no_integrations: Harness):
+    """
+    arrange: Start the Django charm with no integrations specified in the charm.
+    act: Start the django charm and set django-app container to be ready.
+    assert: The charm should be blocked, as Django requires a database to work.
+    """
+    harness = harness_no_integrations
+    container = harness.model.unit.get_container("django-app")
+    container.add_layer("a_layer", DEFAULT_LAYER)
+
+    harness.begin_with_initial_hooks()
+    assert harness.model.unit.status == ops.BlockedStatus(
+        "Django requires a database integration to work"
+    )