Add migration functions

Author: cristaloleg

dbump.go

@@ -31,10 +31,20 @@ type Loader interface {
 
 // Migration represents migration step that will be runned on DB.
 type Migration struct {
-	ID       int    // ID of the migration, unique, positive, starts from 1.
-	Name     string // Name of the migration
-	Apply    string // Apply query
-	Rollback string // Rollback query
+	ID         int         // ID of the migration, unique, positive, starts from 1.
+	Name       string      // Name of the migration
+	Apply      string      // Apply query
+	Rollback   string      // Rollback query
+	ApplyFn    MigrationFn // Apply func
+	RollbackFn MigrationFn // Rollback func
+
+	isQuery bool // shortcut for the type of migration (query or func)
+}
+
+type MigrationFn func(db DB) error
+
+type DB interface {
+	Exec(ctx context.Context, query string, args ...interface{}) error
 }
 
 // Run the Migrator with migration queries provided by the Loader.
@@ -62,7 +72,10 @@ func loadMigrations(ms []*Migration, err error) ([]*Migration, error) {
 		case m.ID > want:
 			return nil, fmt.Errorf("missing migration number: %d (have %d)", want, m.ID)
 		default:
-			// pass
+			if (m.Apply != "" || m.Rollback != "") && (m.ApplyFn != nil || m.RollbackFn != nil) {
+				return nil, fmt.Errorf("mixing queries and functions is not allowed (migration %d)", m.ID)
+			}
+			m.isQuery = m.Apply != ""
 		}
 	}
 	return ms, nil
@@ -115,15 +128,20 @@ func runMigrationExclusive(ctx context.Context, m Migrator, ms []*Migration) err
 	for currentVersion != targetVersion {
 		current := ms[currentVersion]
 		sequence := current.ID
-		query := current.Apply
+		query, queryFn := current.Apply, current.ApplyFn
 
 		if direction == -1 {
 			current = ms[currentVersion-1]
 			sequence = current.ID - 1
-			query = current.Rollback
+			query, queryFn = current.Rollback, current.RollbackFn
 		}
 
-		if err := m.Exec(ctx, query); err != nil {
+		if current.isQuery {
+			err = m.Exec(ctx, query)
+		} else {
+			err = queryFn(m)
+		}
+		if err != nil {
 			return fmt.Errorf("exec: %w", err)
 		}