Fail more gracefully when option collections cleared

[lammia07]

Hi.
When I try to call Html.TextBox on a decimal? Property in a View, with a null value, I get a NullReferenceException.

at Microsoft.AspNetCore.Mvc.DataAnnotations.Internal.NumericClientModelValidator.GetErrorMessage(ModelMetadata modelMetadata)

Can you please provide me with some help.

regards Michael

[Eilon]

@dougbu can you take a look? Some issue with nullable decimals?

[dougbu]

Sure

[javiercn]

I gave a quick try to this yesterday, (just rendering a Product with a decimal? property set to null) and it didn't repro for me, I would test the scenario in which you add an error and render the view again

[javiercn]

@lammia07 Can you provide the full call stack, or even better, a repro for this? What version are you using RC2?

[lammia07]

Hi.
Yes I am using the rc2.
I hope thats okay. I've only got it in german.
The exception occures because the ModelMetadata.ModelBindingMessageProvider is null.

[lammia07]

Yes, I am using rc2.
The exception occurs, because the ViewData.ModelMetadata.ModelBindingMessageProvider is null.
Sry. I have the call stack only in german. I hope it helps.

[lammia07]

Hi.
I have investigated the problem and I think I found the solution.
I have written an own IDisplayMetadataProvider for my DataAnnotations because I want to translate my DataAnnotation with my Database and not with a ResourceFile. Now the problem was calling in my StartupFIle MvcOptions.ModelMetadataDetailsProviders.Clear() and so all Providers were removed. Now i have only replaced the DataAnnotationsMetadataProvider and it works again perfectly.

Sry for bothering you.

Best regards Michael

[rynowak]

Thanks for the update. If this is happening due to clearing something in the options we should give a better error message than just a nullref

[Eilon]

If this is about failing more gracefully, I'm moving it to 1.0.1.

[dougbu]

Went through all MVC-defined options and broke them in two groups. Will send a PR to improve failure modes for the first group.

Worth improving errors when null or empty

MvcOptions

// BodyModelBinder will always throw an UnsupportedContentTypeException.
options.InputFormatters.Clear();
// ModelBinderFactory will always throw an InvalidOperationException, Could not create binder.
options.ModelBinderProviders.Clear();
// ModelMetadata.ModelBindingMessageProvider left null, leading to an NRE. ModelMetadata.IsEnum and
// IsFlagsEnum never true. In-box e.g. [Bind] and DataAnnotations attributes have no impact. No
// excluded bindings or suppressed validations.
options.ModelMetadataDetailsProviders.Clear();
// CompositeModelValidatorProvider will never provide a validator. ValidationVisitor will mark all
// existing ModelState entries as valid.
options.ModelValidatorProviders.Clear();
// HTTP 406 in all ObjectResult cases.
options.OutputFormatters.Clear();

RazorViewEngineOptions

// DefaultRazorViewEngineFileProviderAccessor will not find or watch any files. RazorViewEngine
// will thus never match. InvalidOperationException with expected searched locations.
options.FileProviders.Clear();

MvcViewOptions

// CompositeViewEngine will never match. InvalidOperationException with empty searched locations.
options.ViewEngines.Clear();

Behaviour when null or empty fine as-is

Completely valid for collection to be empty. Or errors occur and are fairly obviously linked to the cleared collection / null value.

MvcOptions

// Dictionary is normally empty. But, if user code added a profile earlier, ResponseCacheAttribute
// will always throw an InvalidOperationException, Profile is not defined.
options.CacheProfiles.Clear();
// No-op. This collection is empty unless AddWebApiConventions() was called.
options.Conventions.Clear();
// UnsupportedContentTypeException not mapped to HTTP 415. TempData not saved or restored. If using
// Web API compat shim, HttpResponseException not mapped to an ObjectResult.
options.Filters.Clear();
// CompositeValueProvider will never provide a value, leading to model binding errors despite data.
options.ValueProviderFactories.Clear();

RazorViewEngineOptions

// No-op. This collection is normally empty.
options.AdditionalCompilationReferences.Clear();
// RazorViewEngine will always throw an ArgumentException, AreaViewLocationFormats cannot be empty.
options.AreaViewLocationFormats.Clear();
// No-op. This collection is empty unless AddLocalizationServices() was called.
options.ViewLocationExpanders.Clear();
// RazorViewEngine will always throw an ArgumentException, ViewLocationFormats cannot be empty.
options.ViewLocationFormats.Clear();

MvcViewOptions

// CompositeClientModelValidatorProvider will not add data- validation attributes. Quiet.
options.ClientModelValidatorProviders.Clear();
// ArgumentNullException when generating id attribute.
options.HtmlHelperOptions.IdAttributeDotReplacement = null;
// ArgumentException when creating TagBuilder.
options.HtmlHelperOptions.ValidationMessageElement = null;
// ArgumentException when creating TagBuilder.
options.HtmlHelperOptions.ValidationSummaryMessageElement = null;

[dougbu]

OutputFormatters was listed in both groups. Fixed.

[dougbu]

Was actually on the fence about MvcOptions.ModelValidatorProviders. After talking w/ @rynowak, decided not to bother changing the behaviour there. Note that behaviour is pretty similar to validating a model type that has no ValidationAttributes.

[dougbu]

Left out checks for MvcOptions.ModelMetadataDetailsProviders. After cleaning up how ModelBindingMessageProvider is initialized, makes sense for this collection to be empty e.g. when using EmptyModelMetadataProvider.

New list of must-not-be-empty options properties:

MvcOptions

// BodyModelBinder will always throw an UnsupportedContentTypeException.
options.InputFormatters.Clear();
// ModelBinderFactory will always throw an InvalidOperationException, Could not create binder.
options.ModelBinderProviders.Clear();
// HTTP 406 in all ObjectResult cases.
options.OutputFormatters.Clear();

RazorViewEngineOptions

// DefaultRazorViewEngineFileProviderAccessor will not find or watch any files. RazorViewEngine
// will thus never match. InvalidOperationException with expected searched locations.
options.FileProviders.Clear();

MvcViewOptions

// CompositeViewEngine will never match. InvalidOperationException with empty searched locations.
options.ViewEngines.Clear();

[dougbu]

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