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Spring binding many-to-many

Wow. This was a lot more complicated than I thought. After several days of research and questions I finally discovered how to make this work. Its all about custom property editors. Please note that many-to-many relationships are not the best thing to use in a production environment. They dont scale well and they are not easy to manage. I later on replaced with Solr, my new favorite implementation.

In this example, many ‘things’ have many ‘tags’ and inversely many ‘tags’ have many ‘things’.

protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) {
   binder.registerCustomEditor(Set.class, “tags”, new CustomCollectionEditor(Set.class) {
     protected Object convertElement(Object element) {
       long id = NumberUtils.parseNumber((String) element, Long.class).longValue();
       Tag tag = tagMgr.getTag(element.toString());

       return new Tag(id, tag.getName);
     }
   });
}

Categories: Software