Disallow Navigation on ForeignKey FieldTemplate – Dynamic Data (UPDATED)

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

C#
[AttributeUsage(AttributeTargets.Property)]
public class DisallowNavigationAttribute : Attribute
{
    public Boolean Hide { get; private set; }

    /// <summary>
    /// Initializes a new instance of the <see cref="DisallowNavigationAttribute"/> class.
    /// </summary>
    public DisallowNavigationAttribute()
    {
        Hide = false;
    }

    public DisallowNavigationAttribute(Boolean show)
    {
        Hide = show;
    }
}

VB
<AttributeUsage(AttributeTargets.[Property] Or AttributeTargets.[Field])> _
Public Class DisallowNavigationAttribute
    Inherits Attribute
    Private _hide As [Boolean]
    Public Property Hide() As [Boolean]
        Get
            Return _hide
        End Get
        Private Set(ByVal value As [Boolean])
            _hide = value
        End Set
    End Property

    Public Sub New(ByVal hide As [Boolean])
        Me.Hide = hide
    End Sub

    Public Sub New()
        Me.Hide = False
    End Sub
End Class

Listing 1 – AllowNavigation attribute

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

C#
/// <summary>
/// Get the attribute or a default instance of the attribute
/// if the Column attribute do not contain the attribute
/// </summary>
/// <typeparam name="T">Attribute type</typeparam>
/// <param name="table">Column to search for the attribute on.</param>
/// <returns>The found attribute or a default instance of the attribute of type T</returns>
public static T GetAttributeOrDefault<T>(this MetaColumn column) where T : Attribute, new()
{
    return column.Attributes.OfType<T>().DefaultIfEmpty(new T()).FirstOrDefault();
}

VB
Imports System.Runtime.CompilerServices
Imports System.Web.DynamicData

Public Module ExtensionMethods

    ''' <summary>
    ''' Get the attribute or a default instance of the attribute
    ''' if the Column attribute do not contain the attribute
    ''' </summary>
    ''' <typeparam name="T">Attribute type</typeparam>
    ''' <param name="column">Column to search for the attribute on.</param>
    ''' <returns>The found attribute or a default instance of the attribute of type T</returns>
    ''' <remarks>Used to simplify getting Attributes from metadata</remarks>
    <Extension()> _
    Public Function GetAttributeOrDefault(Of T As {Attribute, New})(ByVal column As MetaColumn) As T
        Return column.Attributes.OfType(Of T)().DefaultIfEmpty(New T()).FirstOrDefault()
    End Function
End Module

Listing 2 -  Extension method to get attribute

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.

C#
protected string GetNavigateUrl()
{
    var dissallow = Column.GetAttributeOrDefault<DisallowNavigationAttribute>();

    if (!AllowNavigation || dissallow.Hide)
    {
        // remove undeline :D
        HyperLink1.Style.Add(HtmlTextWriterStyle.TextDecoration, "none !important");
        return null;
    }

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

VB
Protected Function GetNavigateUrl() As String
    Dim dissallow = Column.GetAttributeOrDefault(Of DisallowNavigationAttribute)()

    If Not AllowNavigation OrElse dissallow.Hide Then
        Return Nothing
    End If
    If String.IsNullOrEmpty(NavigateUrl) Then
        Return ForeignKeyPath
    Else
        Return BuildForeignKeyPath(NavigateUrl)
    End If
End Function

Listing 3 – ForeignKey FieldTemplate modifications

Updated: With the addition of the inline style the underline will not show, of course you could always just set the CssClass of the Hyperlink to a style with textdecoration: none !important; if you wanted.

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

C#
[MetadataTypeAttribute(typeof(Products.ProductsMetadata))]
public partial class Products
{

    internal sealed class ProductsMetadata
    {
        public object ProductID { get; set; }
        public object ProductName { get; set; }
        public object QuantityPerUnit { get; set; }
        public object UnitPrice { get; set; }
        public object UnitsInStock { get; set; }
        public object UnitsOnOrder { get; set; }
        public object ReorderLevel { get; set; }
        public object Discontinued { get; set; }
        public object Order_Details { get; set; }
        [DisallowNavigation(true)]
        public object Categories { get; set; }
        [DisallowNavigation(true)]
        public object Suppliers { get; set; }
    }
}

VB
Imports Microsoft.VisualBasic
Imports System.Web.DynamicData
Imports System.ComponentModel
Imports System.ComponentModel.DataAnnotations

<MetadataType(GetType([Product].[ProductMD]))> _
Partial Public Class [Product]
    Partial Public Class [ProductMD]
        Public ProductID As Object
        Public ProductName As Object
        Public SupplierID As Object
        Public CategoryID As Object
        Public QuantityPerUnit As Object
        Public UnitPrice As Object
        Public UnitsInStock As Object
        Public UnitsOnOrder As Object
        Public ReorderLevel As Object
        Public Discontinued As Object
        Public Order_Details As Object

        <DisallowNavigationAttribute(True)> _
        Public Category As Object
        Public Supplier As Object
    End Class
End Class

Listing 4 – sample Metadata

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

Happy Coding and remember