Fixed substring function to be 0-based

CHANGELOG.md

@@ -12,6 +12,8 @@ FROST-Server version 2.5 and higher requires Java 21. This is because some libra
 * Set limit to 1 for entity-by-primary-key requests.
 * Improved OpenAPI generator, better property types.
 * Fixed substring not working on PostgreSQL due to failing cast.
+* Fixed substring function to be 0-based. substring(name,1) should return name after
+  the first character, but it returned name including the first character.
 
 
 ## Release version 2.4.0

FROST-Server.SQLjooq/src/main/java/de/fraunhofer/iosb/ilt/frostserver/persistence/pgjooq/PgExpressionHandler.java

@@ -1252,9 +1252,9 @@ public FieldWrapper visit(Substring node) {
             Expression p3 = node.getParameters().get(2);
             FieldWrapper e3 = p3.accept(this);
             Field<Integer> n3 = e3.getFieldAsType(Integer.class, true);
-            return new SimpleFieldWrapper(DSL.substring(s1, n2, n3));
+            return new SimpleFieldWrapper(DSL.substring(s1, n2.add(1), n3));
         }
-        return new SimpleFieldWrapper(DSL.substring(s1, n2));
+        return new SimpleFieldWrapper(DSL.substring(s1, n2.add(1)));
     }
 
     @Override

FROST-Server.Tests/src/test/java/de/fraunhofer/iosb/ilt/statests/c03filtering/FilterTests.java

@@ -264,7 +264,9 @@ void testSubString() throws ServiceFailureException {
         LOGGER.info("  testSubString");
         Dao doa = sSrvc.dao(sMdl.etThing);
 
+        testFilterResults(doa, "substring(properties/string, 1) eq 'wo'", getFromList(THINGS, 2));
         testFilterResults(doa, "substring(properties/string, 1, 1) eq 'w'", getFromList(THINGS, 2));
+        testFilterResults(doa, "substring(name, 4) eq 'g 4'", getFromList(THINGS, 3));
         testFilterResults(doa, "substring(name, 4, 3) eq 'g 4'", getFromList(THINGS, 3));
     }