CODEWITHSUNDEEP
springmodel-view-controllermodelattribute
clark
clark

Reputation: 11

Java Spring @ModelAttribute method model name

I have been reading this forum for quite awhile and find it VERY useful, thank you to the contributors. I have a question that has plagded me for several weeks. And here it goes.

     @RequestMapping(value="updateNote.htm",method=RequestMethod.POST)
     public String updateNote(@ModelAttribute("note")NoteBean nb, BindingResult res,Model model){
        daoobj.updateNote(nb.getName(),nb.getPath(), nb.getNote());

        model.addAttribute("note",daoobj.getByName(nb.getName()));
        return("success");
}

    @RequestMapping(value="updateNote.htm",method=RequestMethod.GET)
    public String updateNote(@ModelAttribute("note")NoteBean nb,Model model){  
        populateNoteBean();
        model.addAttribute("note",daoobj.getByName(nb.getName()));
        return("editNote");
}

@ModelAttribute("WHAT")
  public NoteBean populateNoteBean() {
    NoteBean nnb = new NoteBean();
    return nnb;
  }

With the method populateNoteBean() the model attribute is "WHAT". But, the name that I use is "note". So when I run the code, the NoteBean is correctly saved to the data base. My question is HOW?? It seems that the name "WHAT" should be "note" or that the model attribute is saving it as no name.

Thank for your time.

Upvotes: 1

Views: 1352

Answers (1)

Martin Frey
Martin Frey

Reputation: 10075

With your current code you will have two instances of your notebean in the model!

First spring invokes all modelattribute annotated methods in your controller and places the results in the model. Second it evaluates the ones from your requestmapping method.

The point of a modelattribute annotated method is that you can choose how to create your bean. Load it for example from a database.

We use this approach like that:

  • modelattr method (name="note")

Loads beans from db

  • requestmapping method with modelattr param (name="note")

Merges the note bean created by the first method with the request paramters from a submit for example and you habe directly access to the modifed one.

One nice effect: We do not want to put hidden input fields for all attributes in a form just to be able to merge the entity with the entitymanager. This way you can have a form with only one attribute (plus one for the id to be able to fetch the entity)

Or another one: If your note bean is an abstract class spring has no possibility to instanciate the bean because it does not know what to instanciate. You can for example add a requestparam parameter in the modelattr annotated method and decide what to do yourself.

This is very well described in the documentation. Either the reference or in the api of either controller, reqestmapping or modelattribute i believe.

Upvotes: 1

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