DynamicData Default Values in ForegnKey_Edit & other FieldTemplates

Metadata method

Add a new class the your website called DefaultValueAttribute with the code below.

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

[AttributeUsage(AttributeTargets.Property)]
public class DefaultValueAttribute : System.Attribute
{
    // As implemented, this identifier is merely the Type of the attribute.
    // However, it is intended that the unique identifier be used to identify 
    // two attributes of the same type.
    public override object TypeId { get { return this; } }

    /// <summary>
    /// Constructor
    /// </summary>
    /// <param name="value">String</param>
    public DefaultValueAttribute(String value)
    {
        this._value = value;
    }

    private String _value;
    public String Value
    {
        get { return this._value; }
    }
}

Listing 1 - DefaultValueAttribute

Add your metadata to the appropriate FK fields

[MetadataType(typeof(OrderMetadata))]
public partial class Order
{
}

public class OrderMetadata
{
    [DefaultValue("3")]
    public Object Shipper { get; set; }
}

Listing 2 - Metadata

Open your DynamicData FieldTemplates folder and edit the ForeigKey_Edit.aspx, and add an OnDataBound="DropDownList1_DataBound" entry as in Listing 3

<asp:DropDownList 
    ID="DropDownList1" 
    runat="server" 
    CssClass="droplist" 
    OnDataBound="DropDownList1_DataBound">
</asp:DropDownList>

Listing 3 - Adding the OnDataBound event handler

Next in the code behind file add the DropDownList1_DataBound event handler Listing 4a

protected void DropDownList1_DataBound(object sender, EventArgs e)
{
    // value gotten via a query string as below 
    //string value = Request.QueryString[Column.Name];

    // value gotten via metadata 
    string value = Column.GetDefaultValue();

    if (this.Mode == DataBoundControlMode.Insert && !string.IsNullOrEmpty(value))
    {
        ListItem item = this.DropDownList1.Items.FindByValue(value);
        if (item != null)
        {
            item.Selected = true;
        }
    }
}

Listing 4a - The OnDataBound event handler Metadata version

In this event handler Listing 4a the default value is aquired via the metadata from Listing 2.

Note: the this.Mode == DataBoundControlMode.Insert which makes sure that the auto-fill of default values only occurs for Inserts.

Query String Method

Open your DynamicData FieldTemplates folder and edit the ForeigKey_Edit.aspx, and add an OnDataBound="DropDownList1_DataBound" entry as in Listing 3, next in the code behind file add the DropDownList1_DataBound event handler Listing 4b see Figure 1 for the query string.

protected void DropDownList1_DataBound(object sender, EventArgs e)
{
    // value gotten via a query string as below 
    string value = Request.QueryString[Column.Name];

    //// value gotten via metadata 
    //string value = Column.GetDefaultValue();

    if (this.Mode == DataBoundControlMode.Insert && !string.IsNullOrEmpty(value))
    {
        ListItem item = this.DropDownList1.Items.FindByValue(value);
        if (item != null)
        {
            item.Selected = true;
        }
    }
}

Listing 4b - The OnDataBound event handler QueryString version

Figure 1 - Query String

In Listing 4b event handler all I'm doing is checking for a value passed in the query string see Figure 1 as in this POST from the ASP.Net DynamicData Forum

Other FieldTemplates

This same pattern can be applied to all FieldTemplates for adding default values see Listing 5 which is added to the Text_Edit.ascx FieldTemplate.

protected void TextBox1_PreRender(object sender, EventArgs e)
{
    // Adding a default value to a textbox
    // value aquired via metadata 
    string value = Column.GetDefaultValue();
    if (this.Mode == DataBoundControlMode.Insert && !string.IsNullOrEmpty(value))
    {
        TextBox1.Text = value;
    }
}

Listing 5

Again the value could be acquired either via metadata or query string Listing 6 would replace the line that contains Column.GetdefaultValue().

// value acquired via query string
string value = Request.QueryString[Column.Name];

Listing 6

My feeling on this is you could do all this in the code behind of any of the pages that perform Inserts, on the OnPreRender event however if you put this code in more than one Insert page then you create a code maintenance issue. You will need to make changes in several different places, plus each extra Insert page you create will need this same code adding. However adding this small amount of code to each FieldTemplate you wish to have auto-fill of default values will reduce then amount of maintenance etc.