ASP.NET Core Model Binding Error Messages Localization
To customize framework model binding error messages, you need to set custom accessors for different error message accessors of ModelBindingMessageProvider
.
Example
Here you can download a full source code of what is described in this post. The repository contains example for ASP.NET Core 2.0 (VS 2017.3) and ASP.NET Core 1.1 (VS 2015):
- r-aghaei/AspNetCoreLocalizationSample
Also here you can see the example, live:
- aspnetcorelocalizationsample.azurewebsites.net
Default Error Messages
These are default error messages which the framework shows when model binding to a property fails:
MissingBindRequiredValueAccessor A value for the '{0}' property was not provided.
MissingKeyOrValueAccessor A value is required.
ValueMustNotBeNullAccessor The value '{0}' is invalid.
AttemptedValueIsInvalidAccessor The value '{0}' is not valid for {1}.
UnknownValueIsInvalidAccessor The supplied value is invalid for {0}.
ValueIsInvalidAccessor The value '{0}' is invalid.
ValueMustBeANumberAccessor The field {0} must be a number.
In addition to above messages, ASP.NET Core 2.0 have these messages as well:
MissingRequestBodyRequiredValueAccessor A non-empty request body is required.
NonPropertyAttemptedValueIsInvalidAccessor The value '{0}' is not valid.
NonPropertyUnknownValueIsInvalidAccessor The supplied value is invalid.
NonPropertyValueMustBeANumberAccessor The field must be a number.
Localize ASP.NET Core Model Binding Error Messages
To localize ASP.NET Core model binding error messages, follow these steps:
Create Resource File - Create a resource file under Resources folder in your solution and name the file ModelBindingMessages.fa.resx. The name can be anything else but we will use it to create a localizer. In the example, I used fa (Persian) culture.
Add Resource Keys - Open the resource file and add keys and values which you want to use for localizing error messages. I used keys and values like below image:
Keys which I used are like original messages, except the key for
ValueMustNotBeNull
which was the same asValueIsInvalid
, so I used Null value is invalid. for it.Configure Options - In
ConfigureServices
method, when addingMvc
, configure its options to set message accessors forModelBindingMessageProvider
:public void ConfigureServices(IServiceCollection services) { services.AddLocalization(options => { options.ResourcesPath = "Resources"; }); services.AddMvc(options => { var F = services.BuildServiceProvider().GetService<IStringLocalizerFactory>(); var L = F.Create("ModelBindingMessages", "AspNetCoreLocalizationSample"); options.ModelBindingMessageProvider.ValueIsInvalidAccessor = (x) => L["The value '{0}' is invalid.", x]; options.ModelBindingMessageProvider.ValueMustBeANumberAccessor = (x) => L["The field {0} must be a number.", x]; options.ModelBindingMessageProvider.MissingBindRequiredValueAccessor = (x) => L["A value for the '{0}' property was not provided.", x]; options.ModelBindingMessageProvider.AttemptedValueIsInvalidAccessor = (x, y) => L["The value '{0}' is not valid for {1}.", x, y]; options.ModelBindingMessageProvider.MissingKeyOrValueAccessor = () => L["A value is required."]; options.ModelBindingMessageProvider.UnknownValueIsInvalidAccessor = (x) => L["The supplied value is invalid for {0}.", x]; options.ModelBindingMessageProvider.ValueMustNotBeNullAccessor = (x) => L["Null value is invalid.", x]; }) .AddDataAnnotationsLocalization() .AddViewLocalization(); services.Configure<RequestLocalizationOptions>(options => { var supportedCultures = new[]{new CultureInfo("en"), new CultureInfo("fa")}; options.DefaultRequestCulture = new RequestCulture("en", "en"); options.SupportedCultures = supportedCultures; options.SupportedUICultures = supportedCultures; }); }
Also add this code at beginning of
Configure
method:var supportedCultures = new[] { new CultureInfo("en"), new CultureInfo("fa") }; app.UseRequestLocalization(new RequestLocalizationOptions() { DefaultRequestCulture = new RequestCulture(new CultureInfo("en")), SupportedCultures = supportedCultures, SupportedUICultures = supportedCultures });
Important Note for ASP.NET Core 2.0
In ASP.NET Core 2.0, model binding message provider properties has got read only, but a setter method for each property has been added.
For example, to set
ValueIsInvalidAccessor
, you should useSetValueIsInvalidAccessor()
method this way:options.ModelBindingMessageProvider.SetValueIsInvalidAccessor ( (x) => L["The value '{0}' is invalid.", x]);
With reference to this post that describes in detail the side effects for using BuildServiceProvider inside ConfigureServices, and to this answer regarding resolving services inside ConfigureServices, last but not least, considering the refered improved answer by Andrew Lock, the correct approach to localize model binding error messages should be by creating a custom configuration class that implements IConfigureOptions<T>
then registering it in startup as below:
public class ConfigureModelBindingLocalization : IConfigureOptions<MvcOptions>
{
private readonly IServiceScopeFactory _serviceFactory;
public ConfigureModelBindingLocalization(IServiceScopeFactory serviceFactory)
{
_serviceFactory = serviceFactory;
}
public void Configure(MvcOptions options)
{
using(var scope = _serviceFactory.CreateScope())
{
var provider = scope.ServiceProvider;
var localizer = provider.GetRequiredService<IStringLocalizer>();
options.ModelBindingMessageProvider.SetAttemptedValueIsInvalidAccessor((x, y) =>
localizer["The value '{0}' is not valid for {1}.", x, y]);
options.ModelBindingMessageProvider.SetMissingBindRequiredValueAccessor((x) =>
localizer["A value for the '{0}' parameter or property was not provided.", x]);
options.ModelBindingMessageProvider.SetMissingKeyOrValueAccessor(() =>
localizer["A value is required."]);
options.ModelBindingMessageProvider.SetMissingRequestBodyRequiredValueAccessor(() =>
localizer["A non-empty request body is required."]);
options.ModelBindingMessageProvider.SetNonPropertyAttemptedValueIsInvalidAccessor((x) =>
localizer["The value '{0}' is not valid.", x]);
options.ModelBindingMessageProvider.SetNonPropertyUnknownValueIsInvalidAccessor(() =>
localizer["The supplied value is invalid."]);
options.ModelBindingMessageProvider.SetNonPropertyValueMustBeANumberAccessor(() =>
localizer["The field must be a number."]);
options.ModelBindingMessageProvider.SetUnknownValueIsInvalidAccessor((x) =>
localizer["The supplied value is invalid for {0}.", x]);
options.ModelBindingMessageProvider.SetValueIsInvalidAccessor((x) =>
localizer["The value '{0}' is invalid.", x]);
options.ModelBindingMessageProvider.SetValueMustBeANumberAccessor((x) =>
localizer["The field {0} must be a number.", x]);
options.ModelBindingMessageProvider.SetValueMustNotBeNullAccessor((x) =>
localizer["The value '{0}' is invalid.", x]);
}
}
}
Finally register the new configuration class in startup:
public void ConfigureServices(IServiceCollection services)
{
// ...
services.AddSingleton<IConfigureOptions<MvcOptions>, ConfigureModelBindingLocalization>();
// ...
}