private FieldNode getOwnerField(ClassNode target) {

    List<FieldNode> annotatedFields = getAnnotatedFieldsOfHierarchy(target, OWNER_ANNOTATION);

    if (annotatedFields.isEmpty()) return null;

    if (annotatedFields.size() > 1) {
      addCompileError(
          String.format(
              "Found more than owner key fields, only one is allowed in hierarchy (%s, %s)",
              getQualifiedName(annotatedFields.get(0)), getQualifiedName(annotatedFields.get(1))),
          annotatedFields.get(0));
      return null;
    }

    return annotatedFields.get(0);
  }
  private FieldNode getKeyField(ClassNode target) {

    List<FieldNode> annotatedFields = getAnnotatedFieldsOfHierarchy(target, KEY_ANNOTATION);

    if (annotatedFields.isEmpty()) return null;

    if (annotatedFields.size() > 1) {
      addCompileError(
          String.format(
              "Found more than one key fields, only one is allowed in hierarchy (%s, %s)",
              getQualifiedName(annotatedFields.get(0)), getQualifiedName(annotatedFields.get(1))),
          annotatedFields.get(0));
      return null;
    }

    FieldNode result = annotatedFields.get(0);

    if (!result.getType().equals(ClassHelper.STRING_TYPE)) {
      addCompileError(
          String.format(
              "Key field '%s' must be of type String, but is '%s' instead",
              result.getName(), result.getType().getName()),
          result);
      return null;
    }

    ClassNode ancestor = ASTHelper.getHighestAncestorDSLObject(target);

    if (target.equals(ancestor)) return result;

    FieldNode firstKey = getKeyField(ancestor);

    if (firstKey == null) {
      addCompileError(
          String.format(
              "Inconsistent hierarchy: Toplevel class %s has no key, but child class %s defines '%s'.",
              ancestor.getName(), target.getName(), result.getName()),
          result);
      return null;
    }

    return result;
  }