fix: Migration metrics skipped for configured DBs if if default DB unconfigured

django_prometheus/migrations.py

@@ -38,13 +38,14 @@ def ExportMigrations():
     # ready.
     from django.db.migrations.executor import MigrationExecutor
 
-    if "default" in connections and (isinstance(connections["default"], DatabaseWrapper)):
-        # This is the case where DATABASES = {} in the configuration,
-        # i.e. the user is not using any databases. Django "helpfully"
-        # adds a dummy database and then throws when you try to
-        # actually use it. So we don't do anything, because trying to
-        # export stats would crash the app on startup.
-        return
     for alias in connections.databases:
+        if alias == "default" and (isinstance(connections[alias], DatabaseWrapper)):
+            # This is the case where DATABASES = {} in the configuration,
+            # i.e. the user is not using any databases. Django "helpfully"
+            # adds a dummy database and then throws when you try to
+            # actually use it. So we don't do anything, because trying to
+            # export stats would crash the app on startup.
+            continue
+
         executor = MigrationExecutor(connections[alias])
         ExportMigrationsForDatabase(alias, executor)

django_prometheus/tests/end2end/testapp/test_migrations.py

@@ -1,8 +1,8 @@
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, patch
 
 import pytest
 
-from django_prometheus.migrations import ExportMigrationsForDatabase
+from django_prometheus.migrations import ExportMigrations, ExportMigrationsForDatabase
 from django_prometheus.testutils import assert_metric_equal
 
 
@@ -35,3 +35,76 @@ def test_counters(self):
         assert_metric_equal(0, M("unapplied_total"), connection="fakedb1")
         assert_metric_equal(2, M("applied_total"), connection="fakedb2")
         assert_metric_equal(1, M("unapplied_total"), connection="fakedb2")
+
+
+class TestExportMigrations:
+    """Test ExportMigrations function with mocked connections."""
+
+    @patch("django_prometheus.migrations.connections")
+    @patch("django.db.migrations.executor.MigrationExecutor")
+    def test_export_migrations_with_real_database(self, mock_executor_class, mock_connections):
+        """Test ExportMigrations with a non-empty database connection."""
+
+        # Create a mock connection that is NOT a DatabaseWrapper (dummy)
+        mock_connections.databases = {"default": {}}
+        mock_connection = MagicMock()
+        mock_connection.__class__.__name__ = "RealDatabaseWrapper"
+        mock_connections.__getitem__.return_value = mock_connection
+
+        executor = MagicMock()
+        executor.migration_plan.return_value = ["migration1", "migration2"]
+        executor.loader.applied_migrations = {"m1", "m2", "m3"}
+        mock_executor_class.return_value = executor
+
+        ExportMigrations()
+
+        # Verify MigrationExecutor was called with the connection
+        mock_executor_class.assert_called_once_with(mock_connection)
+        assert executor.migration_plan.call_count == 1
+
+    @patch("django_prometheus.migrations.connections")
+    @patch("django.db.migrations.executor.MigrationExecutor")
+    def test_export_migrations_skips_dummy_database(self, mock_executor_class, mock_connections):
+        """Test ExportMigrations skips dummy database (DATABASES = {} case)."""
+        from django.db.backends.dummy.base import DatabaseWrapper
+
+        # Create a mock connection that IS a DatabaseWrapper (dummy)
+        mock_connections.databases = {"default": {}}
+        mock_dummy_connection = MagicMock(spec=DatabaseWrapper)
+        mock_connections.__getitem__.return_value = mock_dummy_connection
+
+        ExportMigrations()
+
+        # Verify MigrationExecutor was NOT called (because we skip dummy databases)
+        mock_executor_class.assert_not_called()
+
+    @patch("django_prometheus.migrations.connections")
+    @patch("django.db.migrations.executor.MigrationExecutor")
+    def test_export_migrations_with_multiple_databases(self, mock_executor_class, mock_connections):
+        """Test ExportMigrations with multiple databases including a dummy one."""
+        from django.db.backends.dummy.base import DatabaseWrapper
+
+        mock_connections.databases = {"default": {}, "secondary": {}}
+
+        mock_dummy_connection = MagicMock(spec=DatabaseWrapper)
+        mock_real_connection = MagicMock()
+        mock_real_connection.__class__.__name__ = "RealDatabaseWrapper"
+
+        # Setup the connections dict to return different connections for different aliases
+        def get_connection(alias):
+            if alias == "default":
+                return mock_dummy_connection
+            else:
+                return mock_real_connection
+
+        mock_connections.__getitem__.side_effect = get_connection
+
+        executor = MagicMock()
+        executor.migration_plan.return_value = []
+        executor.loader.applied_migrations = set()
+        mock_executor_class.return_value = executor
+
+        ExportMigrations()
+
+        # Verify MigrationExecutor was called only once (for the non-dummy database)
+        mock_executor_class.assert_called_once_with(mock_real_connection)