Disallow Navigation on ForeignKey FieldTemplate – Dynamic Data

This article originates from a post I ding on the ASP.NET Dynamic Data Forum here Re: A few problems with my dynamic data website, Rick Anderson suggesting that it would be a useful post to link to in his FAQ. So here it is for easy access rather than having to search the forum for it.

Firstly the idea is that you want to show the name of the entity but not link to if from the ForeignKey FieldTemplate.

Figure 1 - Category has Navigation disabled

The code we need for this comes in three parts

1. The Attribute
2. The modification the the FieldTemplate
3. The Metadata.

The Attribute

[AttributeUsage(AttributeTargets.Property)]
public class AllowNavigationAttribute : Attribute
{
    public Boolean Show { get; private set; }

    public AllowNavigationAttribute(Boolean show)
    {
        Show = show;
    }
    // this will allow us to have a default set to false
    public static AllowNavigationAttribute Default = new 
        AllowNavigationAttribute(true);
}

Listing 1 – AllowNavigation attribute

Note the use of the Default see Writing Attributes and Extension Methods for Dynamic Data for the details on why.

The modification the the FieldTemplate

Now we need to add a little change to the ForeignKey.aspx.cs file which can be found in the ~/DynamicData/FieldTemplates folder of your Dynamic Data site.

protected string GetNavigateUrl()
{
    var allow = Column.Attributes.OfType<AllowNavigationAttribute>()
                .DefaultIfEmpty(new AllowNavigationAttribute(true))
                .FirstOrDefault().Show;
    if (!AllowNavigation || !allow)
    {
        return null;
    }

    if (String.IsNullOrEmpty(NavigateUrl))
    {
        return ForeignKeyPath;
    }
    else
    {
        return BuildForeignKeyPath(NavigateUrl);
    }
}

Listing 2 – ForeignKey FieldTemplate modifications

All we’ve done here is get the attribute into the allow variable and the add it to the checks in the if statement so that:

• If the internal AllowNavigation is set then null is returned.
• If the custom attribute is set null is returned.

The Metadata

[MetadataType(typeof(ProductMD))]
public partial class Product
{
    public partial class ProductMD
    {
       //EntityRef
        [AllowNavigation(false)]
        public object Category {get;set;}
    }
}

Listing 3 – sample Metadata

Now if you attribute a foreign key column up with the AllowNavigationAttribute you can turn off the hyperlink.

Happy Coding and remember You’re a PC