Add automigrate function to database package. (google#241)

* Add database automigrate.

* Align an error message with common Go formatting conventions

* Improve error message for auto migration failure

---------

Co-authored-by: Dmitry Pasiukevich <dpasiukevich@google.com>

Author: baptmont

session/database/service.go

@@ -43,11 +43,29 @@ type databaseService struct {
 func NewSessionService(dialector gorm.Dialector, opts ...gorm.Option) (session.Service, error) {
 	db, err := gorm.Open(dialector, opts...)
 	if err != nil {
-		return nil, fmt.Errorf("error creating database session service :%w", err)
+		return nil, fmt.Errorf("error creating database session service: %w", err)
 	}
 	return &databaseService{db: db}, nil
 }
 
+// AutoMigrate runs the GORM auto-migration tool to ensure the database schema
+// matches the internal storage models (e.g., storageSession, storageEvent).
+//
+// NOTE: This function relies on a type assertion to the concrete *databaseService
+// implementation. It will return an error if the provided session.Service is
+// a different implementation.
+func AutoMigrate(service session.Service) error {
+	dbservice, ok := service.(*databaseService)
+	if !ok {
+		return fmt.Errorf("invalid session service type")
+	}
+	err := dbservice.db.AutoMigrate(&storageSession{}, &storageEvent{}, &storageAppState{}, &storageUserState{})
+	if err != nil {
+		return fmt.Errorf("auto migrate failed: %w", err)
+	}
+	return nil
+}
+
 // Create generates a session and inserts it to the db, implements session.Service
 func (s *databaseService) Create(ctx context.Context, req *session.CreateRequest) (*session.CreateResponse, error) {
 	if req.AppName == "" || req.UserID == "" {

session/database/service_test.go

@@ -962,8 +962,12 @@ func emptyService(t *testing.T) *databaseService {
 	if err != nil {
 		t.Fatalf("Failed to create session service: %v", err)
 	}
-	dbservice := service.(*databaseService)
-	err = dbservice.db.AutoMigrate(&storageSession{}, &storageEvent{}, &storageAppState{}, &storageUserState{})
+	dbservice, ok := service.(*databaseService)
+	if !ok {
+		t.Fatalf("invalid session service type")
+	}
+
+	err = AutoMigrate(service)
 	if err != nil {
 		t.Fatalf("Failed to AutoMigrate db: %v", err)
 	}