Hiding Foreign Key column Globally in Dynamic Data

This article is based on a question in the Dynamic Data forum Hide Foreign Key Column. And so I thought I’d document what I did for posterity or at least so I can find it again if ever the question arises again :D

So I decided  here is what I would need:

1. An Attribute to mark FK relation ships as hidden.
2. Some Extension methods to extract and test the attribute
3. An IAutoFieldGenerator to filter the Columns on a page

The Attribute

[AttributeUsage(AttributeTargets.Class)]
public class HideFKColumnAttribute : Attribute
{
    public Boolean Hidden { get; set; }
    public HideFKColumnAttribute()
    {
        Hidden = false;
    }

    public HideFKColumnAttribute(Boolean hide)
    {
        Hidden = hide;
    }
}

Listing 1 – HideFKColumnAttribute

This attribute will be set to true if the FK relationship is to be hidden and will default to false to make testing for easy.

The Extension Methods

/// <summary>
/// Test if this FK column should be hidden.
/// </summary>
/// <param name="column">
/// The column to test.
/// </param>
/// <returns>
/// Returns true if it the column should be hidden or false if not.
/// </returns>
public static Boolean FkIsHidden(this MetaColumn column)
{
    var fkColumn = column as MetaForeignKeyColumn;
    if (fkColumn != null)
        return fkColumn.ParentTable.GetAttributeOrDefault<HideFKColumnAttribute>().Hidden;
    else
        return false;
}

/// <summary>
/// Get the attribute or a default instance of the attribute
/// if the Table attribute do not contain the attribute
/// </summary>
/// <typeparam name="T">Attribute type</typeparam>
/// <param name="table">Table 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 MetaTable table) where T : Attribute, new()
{
    return table.Attributes.OfType<T>().DefaultIfEmpty(new T()).FirstOrDefault();
}

Listing 2 – Extension methods

FkIsHidden is used to test if the ParentTable has the HideFKColumnAttribute applied. And the extension method GetAttributeOrDefault returns an HideFKColumnAttribute which is false if not set but true if set explicitly.

The IAutoFieldGenerator class

using System.Collections;
using System.Collections.Generic;
using System.Web.DynamicData;
using System.Web.UI;

public class HideColumnFieldsManager : IAutoFieldGenerator
{
    protected MetaTable _table;
    protected PageTemplate _currentPage;

    public HideColumnFieldsManager(MetaTable table, PageTemplate currentPage)
    {
        _table = table;
        _currentPage = currentPage;
    }

    public ICollection GenerateFields(Control control)
    {
        var oFields = new List<DynamicField>();

        foreach (var column in _table.Columns)
        {
            // carry on the loop at the next column  
            // if scaffold table is set to false or DenyRead
            if (!column.Scaffold ||
                column.IsLongString ||
                column.FkIsHidden())
                continue;

            var f = new DynamicField();

            f.DataField = column.Name;
            oFields.Add(f);
        }
        return oFields;
    }
}

Listing 3 – HideColumnFieldManager

This is the same IAutoFieldGenerator class as used in the article Dynamic Data - Hiding Columns in selected PageTemplates only I’ve added an column.FkIsHidden() to the list of tests for column to display.

I think that about wraps this up, you can download the file from the article mentioned in the paragraph above and then add the extension methods and attribute. Then modify the HideColumnFieldManager class to test for the Hidden FK relationship.

Download