Deserializing JSON to object with no default const

问题:

There are quite a few questions around JSON deserialization but a lot of them seem to be for MVC 1 or MVC 2. I don't seem to have found a satisfactory answer to this specifically for MVC 3.

I have an object with immutable properties and no default constructor, which I want to deserialize to in an ASP.NET MVC 3 application. Here is a simplified version:

public class EmailAddress
{
    public EmailAddress(string nameAndEmailAddress)
    {
        Name = parseNameFromNameAndAddress(nameAndEmailAddress);
        Address = parseAddressFromNameAndAddress(nameAndEmailAddress);
    }

    public EmailAddress(string name, string address)
    {
        Guard.Against<FormatException>(!isNameValid(name), "Value is invalid for EmailAddress.Name: [{0}]", name);
        Guard.Against<FormatException>(!isAddressValid(address), "Value is invalid for EmailAddress.Address: [{0}]", address);
        Name = name;
        Address = address;
    }

    public string Address { get; private set; }
    public string Name { get; private set; }

    // Other stuff
}

An example controller action might be:

[HttpPost]
public ActionResult ShowSomething(EmailAddress emailAddress)
{
    return View(emailAddress)
}

The JSON coming in is:

{"Address":"[e-mail]","Name":"Joe Bloggs"}

What is the best way to get this to deserialize in MVC3? Is there some way of implementing a custom model binder or deserializer class that can handle this?

A solution that doesn't interfere with the object itself would be preferable (ie. a separate deserializer class, rather than adding attributes to properties, etc), although open to any good suggestions.

I found a similar question (with no answer) here: Can I deserialize to an immutable object using JavascriptSerializer?

回答1:

Is there some way of implementing a custom model binder or deserializer class that can handle this?

Yes, you could write a custom model binder:

public class EmailAddressModelBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        var addressKey = "Address";
        var nameKey = "Name";
        if (!string.IsNullOrEmpty(bindingContext.ModelName))
        {
            addressKey = bindingContext.ModelName + "." + addressKey;
            nameKey = bindingContext.ModelName + "." + nameKey;
        }

        var addressValue = bindingContext.ValueProvider.GetValue(addressKey);
        var nameValue = bindingContext.ValueProvider.GetValue(nameKey);
        if (addressValue == null || nameValue == null)
        {
            throw new Exception("You must supply an address and name");
        }
        return new EmailAddress(nameValue.AttemptedValue, addressValue.AttemptedValue);
    }
}

which will be registered in Application_Start:

ModelBinders.Binders.Add(typeof(EmailAddress), new EmailAddressModelBinder());

and finally all that's left is to invoke the action:

$.ajax({
    url: '@Url.Action("ShowSomething")',
    type: 'POST',
    data: JSON.stringify({ "Address": "[e-mail]", "Name": "Joe Bloggs" }),
    contentType: 'application/json',
    succes: function (result) {
        alert('success');
    }
});

回答2:

EDITED ANSWER:

I misread the code, looked at the constructor parameters, instead of the properties.

The cause of your problem is the private set of the properties.

Ie, it should be:

public string Address { get; set; }
public string Name { get; set; }

If you make that change, it should all work.

Just remember:

The model binder looks for PROPERTIES, not the constructor!