Custom DateTime model binder in Asp.net MVC

Question

I would like to write my own model binder for DateTime type. First of all I'd like to write a new attribute that I can attach to my model property like:

[DateTimeFormat("d.M.yyyy")]
public DateTime Birth { get; set,}

This is the easy part. But the binder part is a bit more difficult. I would like to add a new model binder for type DateTime. I can either

• implement IModelBinder interface and write my own BindModel() method
• inherit from DefaultModelBinder and override BindModel() method

My model has a property as seen above (Birth). So when the model tries to bind request data to this property, my model binder's BindModel(controllerContext, bindingContext) gets invoked. Everything ok, but. How do I get property attributes from controller/bindingContext, to parse my date correctly? How can I get to the PropertyDesciptor of property Birth?

Edit

Because of separation of concerns my model class is defined in an assembly that doesn't (and shouldn't) reference System.Web.MVC assembly. Setting custom binding (similar to Scott Hanselman's example) attributes is a no-go here.

Answer 1

For ASP.NET Core, you can use the following custom model binder. A sample model is given below.

public class MyModel
{        
    public string UserName { get; set; }

    [BindProperty(BinderType = typeof(CustomDateTimeBinder))]
    public DateTime Date1 { get; set; }

    [BindProperty(BinderType = typeof(CustomDateTimeBinder))]
    public DateTime? Date2 { get; set; }
} 

The custom binder for DateTime value. It expects the format dd/MM/yyyy.

public class CustomDateTimeBinder : IModelBinder
{
    public Task BindModelAsync(ModelBindingContext bindingContext)
    {
        if (bindingContext == null)
        {
            throw new ArgumentNullException(nameof(bindingContext));
        }

        var modelName = bindingContext.ModelName;

        var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName);

        if (valueProviderResult == ValueProviderResult.None)
        {
            return Task.CompletedTask;
        }

        bindingContext.ModelState.SetModelValue(modelName, valueProviderResult);

        var value = valueProviderResult.FirstValue;

        if (string.IsNullOrEmpty(value))
        {
            return Task.CompletedTask;
        }

        if (!DateTime.TryParseExact(value, "dd/MM/yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out var dateTime))
        {
            var fieldName = string.Join(" ", Regex.Split(modelName, @"(?<!^)(?=[A-Z])"));
            bindingContext.ModelState.TryAddModelError(
                modelName, $"{fieldName} is invalid.");

            return Task.CompletedTask;
        }


        bindingContext.Result = ModelBindingResult.Success(dateTime);
        return Task.CompletedTask;
    }
}

Answer 2

you can change the default model binder to use the user culture using IModelBinder

public class DateTimeBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        bindingContext.ModelState.SetModelValue(bindingContext.ModelName, value);

        return value.ConvertTo(typeof(DateTime), CultureInfo.CurrentCulture);
    }
}

public class NullableDateTimeBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        bindingContext.ModelState.SetModelValue(bindingContext.ModelName, value);

        return value == null
            ? null 
            : value.ConvertTo(typeof(DateTime), CultureInfo.CurrentCulture);
    }
}

And in the Global.Asax add the following to Application_Start():

ModelBinders.Binders.Add(typeof(DateTime), new DateTimeBinder());
ModelBinders.Binders.Add(typeof(DateTime?), new NullableDateTimeBinder());

Read more at this excellent blog that describe why Mvc framework team implemented a default Culture to all users.

Answer 3

You could implement a custom DateTime Binder like so, but you have to take care about the assumed culture and value from the actual client request. May you get an Date like mm/dd/yyyy in en-US and want it to convert in the systems culture en-GB (which it would be like dd/mm/yyyy) or an invariant culture, like we do, then you have to parse it before and using the static facade Convert to change it in its behaviour.

    public class DateTimeModelBinder : IModelBinder
    {
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            var valueResult = bindingContext.ValueProvider
                              .GetValue(bindingContext.ModelName);
            var modelState = new ModelState {Value = valueResult};

            var resDateTime = new DateTime();

            if (valueResult == null) return null;

            if ((bindingContext.ModelType == typeof(DateTime)|| 
                bindingContext.ModelType == typeof(DateTime?)))
            {
                if (bindingContext.ModelName != "Version")
                {
                    try
                    {
                        resDateTime =
                            Convert.ToDateTime(
                                DateTime.Parse(valueResult.AttemptedValue, valueResult.Culture,
                                    DateTimeStyles.AdjustToUniversal).ToUniversalTime(), CultureInfo.InvariantCulture);
                    }
                    catch (Exception e)
                    {
                        modelState.Errors.Add(EnterpriseLibraryHelper.HandleDataLayerException(e));
                    }
                }
                else
                {
                    resDateTime =
                        Convert.ToDateTime(
                            DateTime.Parse(valueResult.AttemptedValue, valueResult.Culture), CultureInfo.InvariantCulture);
                }
            }
            bindingContext.ModelState.Add(bindingContext.ModelName, modelState);
            return resDateTime;
        }
    }

Anyway, culture dependend DateTime parsing in a stateless Application can by a cruelty...Especially when you work with JSON on javascript clientside and backwards.

Answer 4

I had this very big problem myself and after hours of try and fail I got a working solution like you asked.

First of all since having a binder on just a property is not possibile yuo have to implement a full ModelBinder. Since you don't want the bind all the single property but only the one you care you can inherit from DefaultModelBinder and then bind the single property:

public class DateFiexedCultureModelBinder : DefaultModelBinder
{
    protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
    {
        if (propertyDescriptor.PropertyType == typeof(DateTime?))
        {
            try
            {
                var model = bindingContext.Model;
                PropertyInfo property = model.GetType().GetProperty(propertyDescriptor.Name);

                var value = bindingContext.ValueProvider.GetValue(propertyDescriptor.Name);

                if (value != null)
                {
                    System.Globalization.CultureInfo cultureinfo = new System.Globalization.CultureInfo("it-CH");
                    var date = DateTime.Parse(value.AttemptedValue, cultureinfo);
                    property.SetValue(model, date, null);
                }
            }
            catch
            {
                //If something wrong, validation should take care
            }
        }
        else
        {
            base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
        }
    }
}

In my example I'm parsing date with a fiexed culture, but what you want to do is possible. You should create a CustomAttribute (like DateTimeFormatAttribute) and put it over you property:

[DateTimeFormat("d.M.yyyy")]
public DateTime Birth { get; set,}

Now in the BindProperty method, instead of looking for a DateTime property you can look for a property with you DateTimeFormatAttribute, grab the format you specified in the constructor and then parse the date with DateTime.ParseExact

I hope this helps, it took me very long to come with this solution. It was actually easy to have this solution once I knew how to search it :(

Answer 5

I don't think you should put locale-specific attributes on a model.

Two other possible solutions to this problem are:

• Have your pages transliterate dates from the locale-specific format to a generic format such as yyyy-mm-dd in JavaScript. (Works, but requires JavaScript.)
• Write a model binder which considers the current UI culture when parsing dates.

To answer your actual question, the way to get custom attributes (for MVC 2) is to write an AssociatedMetadataProvider.