ASP.NET MVC Model bindING separate day, month, year string fields to single DateTime object

Question

I am currently building a form that requires the user to enter their date of birth. I have determined that the most user friendly way to do this is through separate date day, month, and year input fields.

I have a strongly typed view that contains text boxes for birth day, birth month, and birth year. Once the form is posted to the server I require these posted string values to be converted to a proper DateTime object. I am currently generating this DateTime object in my custom validator that performs age validation tests however I believe there is a far better approach.

So far I have tried building the DateTime object in the model constructor as follows:

public class Applicant
{
    [Required(ErrorMessage = "Day Required")]
    public string DobDay { get; set; }
    [Required(ErrorMessage = "Month Required")]
    public string DobMonth { get; set; }
    [Required(ErrorMessage = "Year Required")]
    [BirthDateValidation("DobDay", "DobMonth")]
    public string DobYear { get; set; }

    public DateTime BirthDate { get; set; }

    public Applicant()
    {
        this.BirthDate = new DateTime(Convert.ToInt32(this.DobYear), Convert.ToInt32(this.DobMonth), Convert.ToInt32(this.DobDay));
    }
}

Is there a way to make this task more automated, as I have tried above, so that when the form is posted to the server a DateTime object is automatically built using the posted birth day, birth month, birth year form values?

Answer 1

Use a custom model binder:

public class MyCustomBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext,
                            ModelBindingContext bindingContext)
    {
        HttpRequestBase request = controllerContext.HttpContext.Request;

        string day = request.Form.Get("DobDay");
        string month = request.Form.Get("DobMonth");
        string year = request.Form.Get("DobYear");
        //etc..
        return new Applicant
        {
            BirthDate = new DateTime(Convert.ToInt32(year), Convert.ToInt32(month), Convert.ToInt32(day))
            //etc..
        };
    }
}

[HttpPost]
public ActionResult Save([ModelBinder(typeof(MyCustomBinder))] Applicant applicant)
{
    return View();
}