Database Lookups

In some situations, you may want to streamline selection of lookup values when users are entering or editing data. For this purpose, lookup fields in Code On Time web applications have the “Activate If Blank” property. If this property is enabled, whenever a user opens an edit view and the lookup is blank, then the lookup window will activate automatically.

Let’s use an example. Create a sample Northwind application. Select the project name on the start page, and press Design.

In the Project Explorer, switch to the Controllers tab. Double-click on Orders / Fields / CustomerID node.

Scroll down and toggle the checkbox next to “Activate If Blank”.

Press OK to save the field.

Enable “Activate If Blank” for EmployeeID and ShipVia fields using the same method. Make sure to save each field. These fields will be activated in the order of the data fields in the view.

Select Browse on the tool bar to generate and open the application in your default web browser. Navigate to the Orders page. On the action bar, press New Orders.

The Customer ID lookup will automatically be activated, as the field is blank.

Select a customer, and the Employee ID lookup will pop up right away.

When you select an employee, then the Ship Via lookup will appear.

This behavior will occur when you edit or create order records that have blank lookup fields, including inline edit or new modes in grid views.

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.