Fix for String filter on empty string received.

dao/src/main/java/org/thingsboard/server/dao/sql/query/EntityKeyMapping.java

@@ -460,32 +460,59 @@ public class EntityKeyMapping {
         }
         switch (stringFilterPredicate.getOperation()) {
             case EQUAL:
-                stringOperationQuery = String.format("%s = :%s", operationField, paramName);
+                stringOperationQuery = String.format("%s = :%s) or (%s is null and :%s = '')", operationField, paramName, operationField, paramName);
                 break;
             case NOT_EQUAL:
-                stringOperationQuery = String.format("%s != :%s", operationField, paramName);
+                stringOperationQuery = String.format("%s != :%s) or (%s is null and :%s != '')", operationField, paramName, operationField, paramName);
                 break;
             case STARTS_WITH:
                 value += "%";
-                stringOperationQuery = String.format("%s like :%s", operationField, paramName);
+                stringOperationQuery = String.format("%s like :%s) or (%s is null and :%s = '%%')", operationField, paramName, operationField, paramName);
                 break;
             case ENDS_WITH:
                 value = "%" + value;
-                stringOperationQuery = String.format("%s like :%s", operationField, paramName);
+                stringOperationQuery = String.format("%s like :%s) or (%s is null and :%s = '%%')", operationField, paramName, operationField, paramName);
                 break;
             case CONTAINS:
                 value = "%" + value + "%";
-                stringOperationQuery = String.format("%s like :%s", operationField, paramName);
+                stringOperationQuery = String.format("%s like :%s) or (%s is null and :%s = '%%%%')", operationField, paramName, operationField, paramName);
                 break;
             case NOT_CONTAINS:
                 value = "%" + value + "%";
-                stringOperationQuery = String.format("%s not like :%s", operationField, paramName);
+                stringOperationQuery = String.format("%s not like :%s) or (%s is null and :%s != '%%%%')", operationField, paramName, operationField, paramName);
                 break;
         }
         ctx.addStringParameter(paramName, value);
-        return String.format("(%s is not null and %s)", field, stringOperationQuery);
+        return String.format("((%s is not null and %s)", field, stringOperationQuery);
     }
 
+
+//            case EQUAL:
+//    stringOperationQuery = String.format("%s = :%s) or (%s is null and :%s = '')", operationField, paramName, operationField, paramName);
+//                break;
+//            case NOT_EQUAL:
+//    stringOperationQuery = String.format("%s != :%s) or (%s is null and :%s != '')", operationField, paramName, operationField, paramName);
+//                break;
+//            case STARTS_WITH:
+//    value += "%";
+//    stringOperationQuery = String.format("%s like :%s) or (%s is null and :%s = '')", operationField, paramName, operationField, paramName);
+//                break;
+//            case ENDS_WITH:
+//    value = "%" + value;
+//    stringOperationQuery = String.format("%s like :%s) or (%s is null and :%s = '')", operationField, paramName, operationField, paramName);
+//                break;
+//            case CONTAINS:
+//    value = "%" + value + "%";
+//    stringOperationQuery = String.format("%s like :%s) or (%s is null and :%s = '')", operationField, paramName, operationField, paramName);
+//                break;
+//            case NOT_CONTAINS:
+//    value = "%" + value + "%";
+//    stringOperationQuery = String.format("%s not like :%s) or (%s is null and :%s != '')", operationField, paramName, operationField, paramName);
+//                break;
+//}
+//        ctx.addStringParameter(paramName, value);
+//                return String.format("((%s is not null and %s)", field, stringOperationQuery);
+
     private String buildNumericPredicateQuery(QueryContext ctx, String field, NumericFilterPredicate numericFilterPredicate) {
         String paramName = getNextParameterName(field);
         ctx.addDoubleParameter(paramName, numericFilterPredicate.getValue().getValue());