Restore missing ModelMetadata properties (additional metadata)

[dougbu]

In addition to #323, the legacy MVC version of ModelMetadata includes the following in its public surface. May need to copy at least some of these over to WebFx for compatibility.

• RequestValidationEnabled, looks like a model binding gap related to the [AllowHtml] attribute but that attribute doesn't seem to exist (yet?)
• PropertiesAsArray, perhaps minor but sorting may be important in some cases
• ShortDisplayName
• Watermark

[dougbu]

Don't need [AllowHtml] or RequestValidationEnabled because we don't have request validation in this system. Leaving that legacy behind in MVC 5.2. Questions on need for other missing properties remain open.

[dougbu]

One more property not present in MVC 6.0's ModelMetadata:

• AdditionalValues, a Dictionary<string, object> which adds a property bag to ModelMetadata and together with [AdditionalMetadata] supports a non-provider way to extend ModelMetadata. Odd the interface is a concrete class rather than IDictionary<string, object>. Either way we probably want this extensibility point (including [AdditionalMetadata]) in MVC 6.0.

[dougbu]

To reiterate, MVC 5 does not rely on these ModelMetadata properties and instead provides the additional metadata for user extensions to read. But MVC 6 doesn't provide this metadata.

The remaining properties are:

• AdditionalValues described just above and linked with the [AdditionalMetadata] attribute that also doesn't exist (yet) in MVC 6.0.
• ShortDisplayName which it turns out MVC 5 writes based on [Display(ShortName="")] when using the non-default metadata provider (DataAnnotationsModelMetadataProvider) but never reads.
• Watermark which it turns out MVC 5 writes based on [Display(Prompt="")] when using the non-default metadata provider (DataAnnotationsModelMetadataProvider) but never reads.

Leave PropertiesAsArray aside since it's internal, likely mostly for performance (a micro-optimization from the looks of it), and doesn't fit well in this issue.

side note: Not writing two of these properties when using the default metadata provider (CachedDataAnnotationsModelMetadataProvider) may be a minor MVC 5 bug. If we add them in MVC 6, might want to provide correct default values.

[dougbu]

See #1758 for an interesting use case of AdditionalValues. Probably possible to create an ugly mess of static dictionaries to work around the missing property but AdditionalValues is the right way forward.

[yishaigalatzer]

Moving out beyond RTM, we will bring back based on user feedback. Seems lower priority for now,

[Aveline67]

Why is the watermark not imlemented and what sould I use instead ?

[dougbu]

@Aveline67 Watermark isn't implemented in MVC 6 because, unlike most ModelMetadata properties, the framework itself doesn't use it and we had not received previous requests for the feature.

One workaround is to add the watermark to AdditionalValues. See for example how [DisplayAttribute(GroupName = "...")] is handled in AdditionalValuesMetadataProvider and how that provider is added in the Startup class for that test site.

[omuleanu]

why is ModelMetadata.AdditionalValues a readonly dictionary, I can't Add anything to it,
in mvc 5 I was using it in custom attributes (IMetadataAware) to add values that would be used in custom helpers and editor templates

[dougbu]

@omuleanu the ModelMetadata.AdditionalValues property is a IReadOnlyDictionary<object, object> to ensure ModelMetadata instances are immutable. Immutability is a requirement for ModelMetadata in the new system.

You should write an IDisplayMetadataProvider implementation which populates DisplayMetadataProviderContext.DisplayMetadata.AdditionalValues as you wish.

[YetaWF]

At least AdditionalMetadata is easy to fix. Sample code implementing an AdditionalMetadataAttribute at
https://yetawf.com/BlogEntry/Title/AdditionalMetadataAttribute%20Anyone/?BlogEntry=1005

[Eilon]

Closing because there are no plans to implement this.