Database Lookups

Suppose that you want to change a field that renders as a textbox into a static drop down list of items, such as the Reorder Level field in the Products controller of the Northwind sample. By default, users can enter any numeric value in the field.

Let’s change this by offering a drop down list of predefined items, and have the item values displayed as words.

You can do this at design time, as explained in Creating Static Lookup Items. However, there may be other situations when you don’t want to change the physical properties of the application. For example, the static items maybe displayed only to users in specific roles. For this purpose, you can use virtualization node sets.

First, you will need to enable shared business rules.

Next, switch to the web application generator, select the project name, and press Develop. This will open the project in Visual Studio.

In the Solution Explorer, navigate to ~/App_Code/Rules/SharedBusinessRules.cs(vb). The code will need to enable virtualization if the controller name is “Products”. The virtualized Products controller will have a modified ReorderLevel field. The Items Style will be changed to “Drop Down List”, and it will have the following static items:

Place the code into your SharedBusinessRules.cs(vb) file:

C#:

using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using MyCompany.Data;

namespace MyCompany.Rules
{
    public partial class SharedBusinessRules : MyCompany.Data.BusinessRules
    {
        public override bool SupportsVirtualization(string controllerName)
        {
            if (controllerName == "Products")
                return true;
            return false;
        }

        protected override void VirtualizeController(string controllerName)
        {
            if (controllerName == "Products")
            {
                NodeSet().SelectField("ReorderLevel")
                    .SetItemsStyle("DropDownList")
                    .CreateItem(0, "Zero")
                    .CreateItem(5, "Five")
                    .CreateItem(10, "Ten")
                    .CreateItem(15, "Fifteen")
                    .CreateItem(20, "Twenty")
                    .CreateItem(25, "Twenty-five")
                    .CreateItem(30, "Thirty");
            }
        }
    }
}

Visual Basic:

Imports MyCompany.Data
Imports System
Imports System.Collections.Generic
Imports System.Data
Imports System.Linq

Namespace MyCompany.Rules

    Partial Public Class SharedBusinessRules
        Inherits MyCompany.Data.BusinessRules

        Public Overrides Function SupportsVirtualization(controllerName As String) As Boolean
            If (controllerName = "Products") Then
                Return True
            Else  
                Return False
            End If
        End Function

        Protected Overrides Sub VirtualizeController(controllerName As String)
            If (controllerName = "Products") Then
                NodeSet().SelectField("ReorderLevel") _
                    .SetItemsStyle("DropDownList") _
                    .CreateItem(0, "Zero") _
                    .CreateItem(5, "Five") _
                    .CreateItem(10, "Ten") _
                    .CreateItem(15, "Fifteen") _
                    .CreateItem(20, "Twenty") _
                    .CreateItem(25, "Twenty-five") _
                    .CreateItem(30, "Thirty")
            End If
        End Sub
    End Class
End Namespace

Save this file and run the web application. You will see that the Products controller now displays Reorder Level filter options as words, and the field is rendered as a drop down list.

In the Products table of Northwind sample database, there is a Reorder Level field. It is rendered as a textbox where users can type in any number to trigger the product reorder. If you look at the available filtering options of the Reorder Level field, you can see that there is a limited number of values stored in the database (0, 5, 10, 15, 20, 25, and 30).

Let’s change this field into a static dropdown list, and have the values displayed as words instead of numbers. For example, “0” will be Zero, “5” will be Five, and so on.

Open the web application generator, select the project name, and select Design. Switch to the Controllers tab in the Project Explorer, and double-click on Products / Fields / Reorder Level node. Change Items Style of Reorder Level field to “Drop Down List”, and press OK to save the field.

Scroll to the top of the Designer, and click on the Items tab. On the action bar, select New | New Item.

Each item represents an option available in the dropdown list. The Value is stored in the database, while the Text is displayed to the user.

Enter the following values:

Press OK to save the item. Using the same method, create more items with the following values:

In the top left corner, press Generate to generate the web app. A Preview window will open. Navigate to Products page, and you will see that the Reorder Level is now displayed with words. Edit a record, and the Reorder Level is now a static dropdown lookup.

The adaptive filter in the Reorder Level column also reflects the static values.

On the action bar, select Report | PDF Document. You will see that Reorder Level displays the Text, and not the Value of the field.