Change default format for DateTime parsing in ASP.NET Core

Had the same problem. While passing DateTime in request body works fine (because Json converter handles this staff), passing DateTime in query string as a parameter has some culture issues.

I did not like the "change all requests culture" approach, bacause this could have impact on other type's parsing, which is not desirable.

So my choise was to override the default DateTime model binding using IModelBinder: https://learn.microsoft.com/en-us/aspnet/core/mvc/advanced/custom-model-binding

What I did:

1) Define custom binder (c# 7 syntax for 'out' parameter is used):

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

        // Try to fetch the value of the argument by name
        var modelName = bindingContext.ModelName;
        var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName);
        if (valueProviderResult == ValueProviderResult.None)
            return Task.CompletedTask;

        bindingContext.ModelState.SetModelValue(modelName, valueProviderResult);

        var dateStr = valueProviderResult.FirstValue;
        // Here you define your custom parsing logic, i.e. using "de-DE" culture
        if (!DateTime.TryParse(dateStr, new CultureInfo("de-DE"), DateTimeStyles.None, out DateTime date))
        {
            bindingContext.ModelState.TryAddModelError(bindingContext.ModelName, "DateTime should be in format 'dd.MM.yyyy HH:mm:ss'");
            return Task.CompletedTask;
        }

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

2) Define provider for your binder:

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

        if (context.Metadata.ModelType == typeof(DateTime) || 
            context.Metadata.ModelType == typeof(DateTime?))
        {
            return new DateTimeModelBinder();
        }

        return null;
    }
}

3) And finally, register your provider to be used by ASP.NET Core:

services.AddMvc(options =>
{
    options.ModelBinderProviders.Insert(0, new DateTimeModelBinderProvider());
});

Now your DateTime will be parsed as expected.

Consider using a custom TypeConverter for your datetime (Source):

using System;
using System.ComponentModel;
using System.Globalization;
using System.Drawing;

public class DeDateTimeConverter : TypeConverter {
   // Overrides the CanConvertFrom method of TypeConverter.
   // The ITypeDescriptorContext interface provides the context for the
   // conversion. Typically, this interface is used at design time to 
   // provide information about the design-time container.
   public override bool CanConvertFrom(ITypeDescriptorContext context, 
      Type sourceType) {

      if (sourceType == typeof(string)) {
         return true;
      }
      return base.CanConvertFrom(context, sourceType);
   }
   // Overrides the ConvertFrom method of TypeConverter.
   public override object ConvertFrom(ITypeDescriptorContext context, 
      CultureInfo culture, object value) {
      if (value is string) {
         if (DateTime.TryParse(((string)value), new CultureInfo("de-DE") /*or use culture*/, DateTimeStyles.None, out DateTime date))
             return date;
      }
      return base.ConvertFrom(context, culture, value);
   }
}

and use TypeConverter attribute on your property:

[TypeConverter(typeof(DeDateTimeConverter))]
public DateTime CustomDateTime { get; set; }

Update

Based on my experience and thanks to this answer and @zdeněk comment, TypeConverter attribute do not work and you should register TypeConverter in Startup.cs:

TypeDescriptor.AddAttributes(typeof(DateTime), new TypeConverterAttribute(typeof(DeDateTimeConverter)));

I wanted to format the dates in my responses and I did the following in ConfigureServices method:

services.AddMvc()
.AddJsonOptions(options =>
{
    options.SerializerSettings.DateFormatString = "mm/dd/yy, dddd";
});

Hope that helps.

Try setting the culture manually in your web.config

<configuration>
   <system.web>    
      <globalization culture="de-DE" uiCulture="de-DE"/>
   </system.web>
</configuration>

EDIT: Since i just realized this is Core, you can do it this way in StartUp.Configure:

var cultureInfo = new CultureInfo("de-DE");
CultureInfo.DefaultThreadCurrentCulture = cultureInfo;
CultureInfo.DefaultThreadCurrentUICulture = cultureInfo;

MVC has always used InvariantCulture for route data and query strings (parameters that go in the URL). The reason behind it is that URLs in localized application must be universal. Otherwise, one url can provide different data depending on the user locale.

You can replace the query and route ValueProviderFactories with your own that respect current culture (or use method="POST" in forms)

public class CustomValueProviderFactory : IValueProviderFactory
{
    public Task CreateValueProviderAsync(ValueProviderFactoryContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        var query = context.ActionContext.HttpContext.Request.Query;
        if (query != null && query.Count > 0)
        {
            var valueProvider = new QueryStringValueProvider(
                BindingSource.Query,
                query,
                CultureInfo.CurrentCulture);

            context.ValueProviders.Add(valueProvider);
        }

        return Task.CompletedTask;
    }
}

services.AddMvc(opts => {
    // 2 - Index QueryStringValueProviderFactory
    opts.ValueProviderFactories[2] = new CustomValueProviderFactory(); 
})

P.S. It is reasonable behavior, but I don't understand why documentation don't cover this very important thing.

Try the following changes

 public class DateTimeConverter : JsonConverter<DateTime>
{
    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        Debug.Assert(typeToConvert == typeof(DateTime));
       
        return  DateTime.ParseExact(reader.GetString(), "yyyy-MM-dd HH:mm:ss", new CultureInfo("de-DE"));
    }

    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(value.ToUniversalTime().ToString("yyyy-MM-dd HH:mm:ss"));
    }
}

and

builder.Services.AddMvc().AddJsonOptions(options =>
{
    options.JsonSerializerOptions.Converters.Add(new DateTimeConverter());
});

}

Hope this would help.

              using System;
        using System.Collections.Generic;
        using System.Linq;
        using System.Threading.Tasks;
        using Microsoft.AspNetCore.Builder;
        using Microsoft.AspNetCore.Hosting;
        using Microsoft.Extensions.Configuration;
        using Microsoft.Extensions.DependencyInjection;
        using Microsoft.Extensions.Logging;
        using Microsoft.Extensions.Options;
        using System.Globalization;
        using Microsoft.AspNetCore.Localization;

        namespace coreweb
        {
            public class Startup
            {
                public Startup(IHostingEnvironment env)
                {
                    var builder = new ConfigurationBuilder()
                        .SetBasePath(env.ContentRootPath)
                        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                        .AddEnvironmentVariables();

                    if (env.IsDevelopment())
                    {
                        // This will push telemetry data through Application Insights pipeline faster, allowing you to view results immediately.
                        builder.AddApplicationInsightsSettings(developerMode: true);
                    }
                    Configuration = builder.Build();
                }

                public IConfigurationRoot Configuration { get; }

                // This method gets called by the runtime. Use this method to add services to the container.
                public void ConfigureServices(IServiceCollection services)
                {
                    // ... previous configuration not shown
                    services.AddMvc();
                    services.Configure<RequestLocalizationOptions>(
                        opts =>
                        {
                            var supportedCultures = new[]
                            {

                        new CultureInfo("de-DE"),
                            };

                            opts.DefaultRequestCulture = new RequestCulture("de-DE");
                    // Formatting numbers, dates, etc.
                    opts.SupportedCultures = supportedCultures;
                    // UI strings that we have localized.
                    opts.SupportedUICultures = supportedCultures;
                        });
                }

                // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
                public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
                {
                    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
                    loggerFactory.AddDebug();

                 //   app.UseApplicationInsightsRequestTelemetry();

                    if (env.IsDevelopment())
                    {
                        app.UseDeveloperExceptionPage();
                        app.UseBrowserLink();
                    }
                    else
                    {
                        app.UseExceptionHandler("/Home/Error");
                    }

                  //  app.UseApplicationInsightsExceptionTelemetry();

                    app.UseStaticFiles();

                    var options = app.ApplicationServices.GetService<IOptions<RequestLocalizationOptions>>();
                    app.UseRequestLocalization(options.Value);



                    app.UseMvc(routes =>
                    {
                        routes.MapRoute(
                            name: "default",
                            template: "{controller=Home}/{action=Index}/{id?}");
                    });
                }
            }
        }

If you don't mind using the generic StatusCode method to make this call, you can do something like the following:

internal IActionResult CreateResponse(int code, object content = null)
    {
        Type t = content?.GetType();
        bool textContent = t == typeof(string) || t == typeof(bool);
        //
        JsonSerializerSettings dateFormatSettings = new JsonSerializerSettings
        {

            DateFormatString = myDateFormat
        };

        string bodyContent = content == null || string.IsNullOrWhiteSpace(content + "")
                    ? null
                    : textContent
                        ? content + ""
                        : JsonConvert.SerializeObject(content, dateFormatSettings);

        ObjectResult or = base.StatusCode(code, bodyContent);
        string mediaType = 
                    !textContent
                        ? "application/json"
                        : "text/plain";
        or.ContentTypes.Add(new MediaTypeHeaderValue(mediaType));
        return or;
    }

You can add this to a base class and call it like:

return base.CreateResponse(StatusCodes.Status200OK, new { name = "My Name", age = 23});

It's up to you if you want to create your own Ok, BadRequest, etc...methods, but for me this works and I hope it helps anybody else. You could even default int code = 200, if most of your requests are GETs. This code assumes you either want to respond with a string, boolean, or a custom object, but you can easily handle all primitives by checking Type.GetTypeInfo().IsPrimitive and even doing some checks for decimal, string, DateTime, TimeSpan, DateTimeOffset, or Guid.

I had same problem ad almost got mad. I tried everthing with no sucsses. First I found a workaround to solve part of my problem:

Workaround:

string data1 
string horainicio 
string horafim

var ageData = new AgendaData();
var user = await _userManager.GetUserAsync(User);
string usuario = user.Id;
int empresa = user.IdEmpresa;
int Idprospect = Convert.ToInt32(prospect);
int minutos = 0;           
var tipoAgenda = TipoAgenda.Contato;

var provider = CultureInfo.InvariantCulture;
provider = new CultureInfo("en-US");            
string formato = "dd/MM/yyyy HH:mm";

var dataInicio = DateTime.ParseExact(data1 + " " + horainicio, formato, provider);
var dataFim = DateTime.ParseExact(data1 + " " + horafim, formato, provider);           
var dataAlerta = dataInicio.AddMinutes(-minutos);

But, this way i aways have to set invariantculture to all my datetime. I found the solution setting my culture at the configure on startup.cs.

Set Culture on startup.cs

 public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, CRMContext context)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseDatabaseErrorPage();
                app.UseBrowserLink();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }

            //Fixar Cultura para en-US
            RequestLocalizationOptions localizationOptions = new RequestLocalizationOptions
            {
                SupportedCultures = new List<CultureInfo> { new CultureInfo("en-US") },
                SupportedUICultures = new List<CultureInfo> { new CultureInfo("en-US") },
                DefaultRequestCulture = new RequestCulture("en-US")
            };

            app.UseRequestLocalization(localizationOptions);      
            app.UseStaticFiles();
            app.UseIdentity();

            // Add external authentication middleware below. To configure them please see https://go.microsoft.com/fwlink/?LinkID=532715

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });

            context.Database.EnsureCreated();
        }

Hope this help you.