c# - Aspnet Core Decimal binding not working on non English Culture

Question

I have an aspnet core app that runs with a non english configuration (spanish):

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        ......
        app.UseRequestLocalization(new RequestLocalizationOptions
        {
            DefaultRequestCulture = new RequestCulture(new CultureInfo("es-AR"))
            ,SupportedCultures = new List<CultureInfo>
            {
                new CultureInfo("es-AR")
            }
            ,SupportedUICultures = new List<CultureInfo>
            {
                new CultureInfo("es")
            }
        });

        .........
    }

In english a decimal number has its decimal part delimited with a dot, but in spanish a comma is used:

• 10256.35 english
• 10256,35 spanish

I have this action in a controller:

 [HttpPost]
 public decimal Test(decimal val)
 {
     return val;
 }

If I use postman and send to that action a json like this {val: 15.30}, then val in the action recives a 0 (binding not working because of the culture). If I send a json like this {val: 15,30} then in the action I recive 15.30 The problem I have is, I need the action to accept decimals with commas, because that is the format that comes from inputs type text in the app's forms. But i also need to accept decimal with a dot that comes from request in json format. There is no way to specify a decimal/float in json that accepts a comma (send it as string is not an option). How can I do this??? I'm driving my self crazy with this.

Thanks!!

Answer 1

Apparently, the decimal binding in ASP.NET core 1.0.0 is not culture invariant by default. The model binding depends on the server culture.

You can change this behavior with a custom model binding as suggested by Stephen Muecke. Here is mine based on Custom Model Binding in ASP.Net Core 1.0 (RTM)

public class InvariantDecimalModelBinderProvider : IModelBinderProvider
{
    public IModelBinder GetBinder(ModelBinderProviderContext context)
    {
        if (context == null) throw new ArgumentNullException(nameof(context));

        if (!context.Metadata.IsComplexType && (context.Metadata.ModelType == typeof(decimal) || context.Metadata.ModelType == typeof(decimal?)))
        {
            return new InvariantDecimalModelBinder(context.Metadata.ModelType);
        }

        return null;
    }
}

public class InvariantDecimalModelBinder : IModelBinder
{
    private readonly SimpleTypeModelBinder _baseBinder;

    public InvariantDecimalModelBinder(Type modelType)
    {
        _baseBinder = new SimpleTypeModelBinder(modelType);
    }

    public Task BindModelAsync(ModelBindingContext bindingContext)
    {
        if (bindingContext == null) throw new ArgumentNullException(nameof(bindingContext));

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

        if (valueProviderResult != ValueProviderResult.None)
        {
            bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);

            var valueAsString = valueProviderResult.FirstValue;
            decimal result;

            // Use invariant culture
            if (decimal.TryParse(valueAsString, NumberStyles.AllowDecimalPoint | NumberStyles.AllowLeadingSign, CultureInfo.InvariantCulture, out result))
            {
                bindingContext.Result = ModelBindingResult.Success(result);
                return Task.CompletedTask;
            }
        }

        // If we haven't handled it, then we'll let the base SimpleTypeModelBinder handle it
        return _baseBinder.BindModelAsync(bindingContext);
    }
}

And in Startup.cs:

services.AddMvc(config =>
{
    config.ModelBinderProviders.Insert(0, new InvariantDecimalModelBinderProvider());
});