Retrieve model name in custom display name attribute

Question

Here is my development requirement,

My label values are stored in the database, and I still want to use the data annotation in a declarative way, this is to make my model more readable.

And here is my approach,

I decided to write custom DisplayNameAttribute, where the default value provided by my model will be overwritten by the value retrieved from the database.

Here is the property defined in the model,

    [CustomDisplay(Name: "First Name")]
    [CustomRequired(ErrorMessage: "{0} is required")]
    public String FirstName { get; set; }

Here is the custom display name attribute class,

public class CustomDisplayAttribute : DisplayNameAttribute
{
    private string _defaultName;
    private string _displayName;

    public CustomDisplayAttribute(string Name)
    {
        _defaultName = Name;
    }

    public override string DisplayName
    {
        get
        {
            if (String.IsNullOrEmpty(_displayName))
            {
                _displayName = DAO.RetrieveValue(**ModelName**, _defaultName);
            }
            return _displayName;
        }
    }
}

Now, you can see in the above code, ModelName is something I need, but I don't have!!

While debugging, I dig into ModelMetadataProviders.Current and can see the availability of the current model in action. But, as it is part of non-public static members I am unable to access it through my code.

I have written the below method to retrieve the model name through reflection,

private static string GetModelName()
{
    var modelName = String.Empty;
    FieldInfo info = typeof(CachedAssociatedMetadataProvider<CachedDataAnnotationsModelMetadata>)
                        .GetField("_typeIds", BindingFlags.NonPublic | BindingFlags.Static);
    var types = (ConcurrentDictionary<Type, string>)info.GetValue(null);
    modelName = types.FirstOrDefault().Key.Name;
    return modelName;
}

But the problem is, the types collection provides me entries for all the models (visited at least once by the user). And there is no clue to know, which is currently in action!!

Erik Philips · Answer 1 · 2017-01-24T22:16:35.030

IMHO Attributes should not be used to make database calls. Attributes should be used to add metadata to Classes/Properties etc...

So If you're willing to change your code to be more like the Microsoft architecture for MVC then you'd have your custom Attribute and a custom ModelMetadataProvider:

public class CustomDisplayAttribute : Attribute
{
    public CustomDisplayAttribute(string name)
    {
        Name = name;
    }

    public string Name { get; private set; }
}

Then a new ModelMetadataProvider:

public class DatabaseModelMetadataProvider : DataAnnotationsModelMetadataProvider
{
  public DatabaseModelMetadataProvider()
  {
  }

  protected override ModelMetadata CreateMetadata(
    IEnumerable<Attribute> attributes, 
    Type containerType, 
    Func<object> modelAccessor, 
    Type modelType, 
    string propertyName)
  {
    var metadata = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);

    var displayAttribute = containerType == null
        ? null as CustomDisplayAttribute
        : containerType.GetProperty(propertyName)
           .GetCustomAttributes(false)
           .OfType<CustomDisplayAttribute>()
           .FirstOrDefault();
    if (displayAttribute != null)
    {
      var displayValue = DAO.RetrieveValue(containerType.ToString(), displayAttribute.Name)

      metadata.DisplayName = displayValue;
    }
    return metadata;
  }
}

Where

public class MyViewModel
{
  public MyPropertyType PropertyName { get; set; }
}

containerType = MyViewModel
modelType = MyPropertyType
propertyName = PropertyName

Then register the provider (global.asax or whatever):

ModelMetadataProviders.Current = new LocalizedModelMetadataProvider();

Also you can take a look at the ModelMetadata it has a few other things you might want to change in the future.

Retrieve model name in custom display name attribute

1 Answers1