fix(dalgorm): make DropIndexes idempotent by skipping missing indexes

GORM's DropIndex emits a bare `DROP INDEX` without `IF EXISTS`, which makes PostgreSQL fail with SQLSTATE 42704 when the target index is absent (e.g. it was already removed by an earlier column rewrite via ChangeColumnsType). Guard each drop with HasIndex so the operation is idempotent and database-neutral, without swallowing genuine errors.

Signed-off-by: DoDiODev <DoDiDev@proton.me>

Author: DoDiODev

backend/impls/dalgorm/dalgorm.go

@@ -452,9 +452,18 @@ func (d *Dalgorm) RenameTable(oldName, newName string) errors.Error {
 
 // DropIndexes drops indexes for specified table
 func (d *Dalgorm) DropIndexes(table string, indexNames ...string) errors.Error {
+	migrator := d.db.Migrator()
 	for _, indexName := range indexNames {
-		err := d.db.Migrator().DropIndex(table, indexName)
-		if err != nil {
+		// Skip indexes that are not present so the operation is idempotent and
+		// database-neutral. GORM's DropIndex emits a bare `DROP INDEX` (without
+		// `IF EXISTS`), which makes PostgreSQL fail with SQLSTATE 42704 when the
+		// index is missing (e.g. it was already removed by an earlier column
+		// rewrite). Guarding with HasIndex keeps genuine errors from being
+		// swallowed while making repeated/partial migrations safe.
+		if !migrator.HasIndex(table, indexName) {
+			continue
+		}
+		if err := migrator.DropIndex(table, indexName); err != nil {
 			return d.convertGormError(err)
 		}
 	}