@Override
    public String toString() {
        JPQLSerializer serializer = new JPQLSerializer(templates, entityManager);
        serializer.serializeForInsert(queryMixin.getMetadata(), inserts.isEmpty() ? columns : inserts.keySet(), values, subQuery, inserts);
        return serializer.toString();
    }
UpdateClause implementation for JPA

@author tiwe
querydsl-jpa/src/main/java/com/querydsl/jpa/impl/JPAInsertClause.java