Metadata and Metadata Attributes

We already used the DisplayAttribute to specify the display name of properties and the DataTypeAttribute to further constrain a property type, specifying if a DateTime represents a date, a time, or a full DateTime, etc.

The above attributes are used by the ASP.NET Core framework itself to decide how to render ViewModel properties. There are also other attributes supported by ASP.NET Core we can use to define further property features. They are not used directly by ASP.NET Core default tag helpers, but they are available in our views so we can use them in our view code or also, in the definition of our custom tag helpers.

MetaData and MetaData providers

All metadata collected by the framework is available in all views through the ViewData.ModelExplorer property. More specifically, ViewData.ModelExplorer.Metadata contains all metadata associated with the view ViewModel. Metadata is useful for deciding how to render simple properties, so we should use ViewData.ModelExplorer.Metadata only when the view ViewModel is a simple property.

When the view ViewModel is a complex type, we should use ViewData.ModelExplorer.GetExplorerForProperty(string name), instead. It returns all ModelExplorer instances associated with each property of the ViewModel. The code below shows an example: