A1 Repro (ASP.Net CORE): Loading Lookup Collection in Action Filter and Simple Dropdownlist Editor

There are times when a collection of lookup to populate a drop down list is needed; this is very common. The usual solution is to create an Enumerable property in the view model to hold the lookup values, inject a service in the controller then in the action load the list to the view model and load the view. A complete example can be accessed at Pluralsight where dropdown lists are polulated in Razor views using the MVVM design pattern, Entity Framework, and Ajax.

Another approach is to load the lookup collection to the ViewData and access the values from the view or a template editor. This note is about a modification of this approach where the lookup collection is loaded into the ViewData using a Fiter Service which decorates the action requiring the loopkup collection.

The Filter
The following filter loads a collection of AssetTypes and converts the collection of DTOs into a SelectListItems using an extension method and loads the list on the ViewData.



The way to consume this filter service attribute is through the ServiceFilter, decorating the action with [ServiceFilter(typeof(AssetTypeCollectionAttribute))] this way:



Inject Service
Like any other service, the Filter Service needs to be injected in order to be discovered, therefore for an ASP.Net CORE application AssetTypeCollectionAttribute needs to  be injected.  In this example is added for the scope of the request:



Simple Drop Down List Editor
The editor template is simple, and can be reused for other lookup lists.



ViewModel and View
To end the note; the editor is invoked from the view passing two parameters in the ViewData; the index or key used to store the collection in the ViewData and the initial default message to load in the drop down list.



None of the above would work if the ViewModel does not have property AssetType decorated with [UIHint("ViewDropdown")]

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