Spring 3 @ModelAttribute with List in model

Question

I have two models :

public class Size {
    private String name;
        // getter and setter
}

public class Product {
    private int id;
    private String designation;
    private Float price;
    private List<Size> availableSizes;
        // Getter and setters
}

I have defined Sizes in my servlet, and now I nead to create products with the availables sizes.

What I do in my index Controller:

ModelAndView render = new ModelAndView("admin/index");
render.addObject("products", productFactory.getProducts());
render.addObject("sizes", sizeFactory.getSizes());
render.addObject("command", p);
return render;

I've a list of products, and my list of sizes.

In my index view, I do:

<form:form method="post" action="/ecommerce/admin/products" class="form-horizontal">
       <form:input path="id" />
    <form:input path="designation" />
    <form:input path="price" />
    <form:select path="availableSizes" items="${sizes}"/>
    <input type="submit" value="Ajouter le produit" class="btn" />
</form:form>

Then, in new product controller, I do :

// To fix: Sizes not saved !
@RequestMapping(value = "/products", method = RequestMethod.POST)
    public ModelAndView newProduct(@ModelAttribute("Product") Product product,
            BindingResult result) {
        productFactory.add(product);
        return buildIndexRender(null, null, product);
    }

The problem is that I keet the posted product, but not the corresponding sizes.

Is there a way to keep selected sizes in the form int the controler, or directly in the model?

Thanks.

Answer 1

It's a very common problem.

To set a List<Size> in Product instance from the post data, that is a string colon separated list with selected sizes, all you need to do is tell the framework how to convert a size String to a Size instance. The most common approach is registering a PropertyEditor on WebDataBinder

class SizePropertyEditor extends PropertyEditorSupport {

        @Override
        public void setAsText(String text) throws IllegalArgumentException {
            Size size = stringToSize(text);  // write this code
            setValue(size);
        }
}

and register the property editor in Controller using @InitBinder annotation

@InitBinder
public void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(Size.class, new SizePropertyEditor());

}

For a more generic approach see ConversionService.