code: public boolean execDelete(Class<? extends D6Model> modelObj) {
  
      boolean retVal = false;
  
      final D6CrudDeleteHelper dh = new D6CrudDeleteHelper(modelObj);
      final String updateSQL = dh.createDeleteAllPreparedSQLStatement();
  
      log("#execDelete model=" + modelObj + " deleteSQL=" + updateSQL);
  
      final Connection conn = createConnection();
  
      try {
  
        PreparedStatement preparedStmt = null;
  
        // There is a possibility that the error occurs in one single delete
        // statement.
        // Therefore, turn the auto commit off.
        conn.setAutoCommit(false);
  
        preparedStmt = conn.prepareStatement(updateSQL);
  
        // execute SQL
        preparedStmt.executeUpdate();
  
        // Finally, commit.
        conn.commit();
  
        retVal = true;
  
      } catch (SQLException e) {
  
        loge("#execDelete", e);
        retVal = false;
  
      } finally {
        try {
          conn.close();
        } catch (SQLException e) {
          retVal = false;
          loge("#execDelete", e);
        }
      }
      return retVal;
  
    }
docs: Delete the appropriate line in the specified model object
  
  @param modelObj
  @return true:DB operation success false:failure