code: private String buildConstraintExpr(String device_name, String attribute, String event_name, String[] filters) {
          String str =
                  "$domain_name == \'" + device_name.toLowerCase() + "/" +
                          attribute.toLowerCase() + "\'" + " and $event_name == \'" +
                          event_name + "\'";
          if (filters != null && filters.length != 0) {
              str += " and ((";
              for (String filter : filters)
                  str += filter;
              str += " ) and $forced_event > 0.5 )";
          }
          return str;
      }
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