Tuesday, September 11, 2012

Creating Calculated Fields

The picture below shows the Order Details form in edit mode.

Order Details edit form displayed without an Extended Price field.

Let’s create a calculated field called Extended Price that will display the extended price of the Order Details item.

Calculated fields are also known as virtual fields. The field value is not stored in the database - it is calculated at runtime based on values of other fields in the data row.

Creating the virtual Field

Activate the Project Designer. In the Project Explorer, switch to the Controllers tab. Right-click on OrderDetails / Fields node, and press New Field.

New Field context menu option for OrderDetails controller in the Project Explorer.

Assign the following values:

Property Value
Name ExtendedPrice
Type Currency
Label Extended Price
Allow Query-by-Example true
Allow Sorting true

Press OK to save. Drag OrderDetails / Fields / ExtendedPrice node onto OrderDetails / Views / grid1 node to bind the field to the view grid1.

Dragging ExtendedPrice field node onto 'grid1' view.     Data field 'ExtendedPrice' created in view 'grid1'.

Drag OrderDetails / Fields / ExtendedPrice node onto OrderDetails / Views / editForm1 / c1 – Order Details node to bind the field to view editForm1.

Dragging 'ExtendedPrice' field onto 'c1 - Order Details' category node.     Data Field 'ExtendedPrice' created in 'c1 - Order Details' category.

Finally, drag OrderDetails / Fields / ExtendedPrice node onto OrderDetails / Views / createForm1 node.

Dragging 'ExtendedPrice' field onto 'createForm1' view node.     Data field 'ExtendedPrice' created in view 'createForm1'.

A binding of field to a view is called a data field.

On the toolbar, press Browse and navigate to the Order Manager page. The Extended Price data field is visible in the grid and in the form views of Order Details. However, the field is rendered as blank.

Extended Price field is available as a blank field in grid view and create form.

Note that if you have a custom category template associated with the form view, then the field will not be visible automatically. In that case, the custom category template for editForm1 needs to be updated to display the data field.

Read the next section to learn how to include the new virtual data field in the template, or skip to the following section discussing how to provide an SQL Formula for the field.

Updating the Custom Category Template

Switch to the Project Designer. In the Project Explorer, switch to the Pages tab. Right-click on Order Manager / c103 / control1 node and press Edit in Visual Studio.

Edit in Visual Studio context menu option in the Project Explorer.

The template file will be opened in Visual Studio. Replace the existing code after the <%@ Control %> element with the following:

<div style="display: none;">
    <div id="OrderDetails_editForm1_c1">
        <table>
            <tr>
                <td style="padding-right: 36px;font-weight:bold;">Product:</td>
                <td style="padding-right: 18px;">
                    <span class="FieldPlaceholder DataOnly">{ProductID}</span>
                </td>
                <td style="padding-right: 18px;">Discount:</td>
                <td>
                    <span class="FieldPlaceholder DataOnly">{Discount}</span>
                </td>                
            </tr>
            <tr>
                <td>Unit Price:</td>
                <td>
                    <span class="FieldPlaceholder DataOnly">{UnitPrice}</span>
                </td>
                <td>Quantity:</td>
                <td>
                    <span class="FieldPlaceholder DataOnly">{Quantity}</span>
                </td>
                <td style="padding-left:18px;"><i>Extended Price:</i></td>
                <td>
                    <span class="FieldPlaceholder DataOnly">{ExtendedPrice}</span>
                </td>
            </tr>
        </table>
    </div>
</div>

Save the file, and refresh the webpage. The Extended Price data field will be displayed in edit form.

Extended Price field has been added to the Order Details category.

SQL Formula

Let’s provide an SQL expression evaluated when the data rows of order details are selected from the database.

In the Project Explorer, switch to the Controllers tab and double-click on OrderDetails / Fields / ExtendedPrice node.

ExtendedPrice field node of OrderDetails controller in the Project Explorer.

Change the following:

Property New Value
The value of this field is computed at run-time by SQL expression. true
SQL Formula
OrderDetails.UnitPrice * OrderDetails.Quantity * (1 - OrderDetails.Discount)
Values of this field cannot be edited true
Data Format String c

Press OK to save the field. On the toolbar, press Browse. The Extended Price field will not be editable, and the value will be presented when the form is rendered.

Extended Price is rendered as a read-only field that is calculated when the form is rendered.

SQL Formula provides the highest possible performance for the calculation since it is being evaluated by the database engine. The complexity of calculated fields depends on the capabilities of the database engine. There are numerous built-in functions that the developer can take advantage of.

Fields based on SQL Formula can be sorted and filtered with the highest possible performance as well.

Calculating Field Values Just-in-Time

Extended Price is not recalculated when a user changes values of Unit Price, Discount, or Quantity fields.

Extended Price field is not updated when the other fields are changed.

The SQL Formula of the Extended Price field is evaluated only when the data is selected from the database. If the user makes changes in the browser window, the values will not be submitted to the server until the record is saved. Developers can implement a server-side or client-side calculation that will be performed just-in-time as users change the values of the formula’s base fields.

The application framework includes a business rule engine that allows implementing rules in SQL, C#/Visual Basic, or JavaScript.

SQL and C#/Visual Basic business rules require a round-trip between the web browser and the web server. They can look up database information and interact with external systems when necessary.

JavaScript business rules are executed in the browser and provide the highest possible performance when server-side data is not required for calculation.

Let’s consider implementing the calculation using all three flavors of business rules. Note that the developer needs only one of them to accomplish just-in-time calculation of Extended Price.

SQL Business Rule

In the Project Explorer, double-click on OrderDetails / Fields / ExtendedPrice node.

ExtendedPrice field in the OrderDetails controller.

Make the following changes:

Property New Value
The value of this field is calculated by a business rule expression. true
Context Fields UnitPrice,Quantity,Discount

Press OK to save. Right-click on OrderDetails / Business Rules node, and press New Business Rule.

New Business Rule context menu option for OrderDetails controller in the Project Explorer.

Assign these values:

Property Value
Type SQL
Command Name Calculate
Phase Execute
Script
set @ExtendedPrice = @UnitPrice * @Quantity * (1 - @Discount)

Press OK to save. On the toolbar, press Browse. Select and start editing an Order Details record.

Order Details form without any changed values.

Change the value in Quantity field. Press Enter or shift the focus to a different field. The Extended Price will be updated.

When focus is shifted away from the field, the Extended Price field will be recalculated.

The client library executes Calculate action, which causes transfer of field values to the server. The application framework will pass the business rule script along with the parameter values to the database engine for execution. Then, it evaluates parameters and returns changed values to the client web browser.

SQL business rules involve client, application server, and database engine tiers. The advantage of SQL business rules is the ability to access any database information when necessary.

Code Business Rule

The business rule can also be implemented using C# or Visual Basic.

If you have the SQL business rule created in the previous section, then you will need to delete or rename the business rule. Double-click on OrderDetails / Business Rules / Calculate node.

Calculate business rule in Order Details controller.

Change the Command Name property:

Property Value
Command Name DoNotRun

Press OK to save. Alternatively, business rule r100 can be deleted.

Right-click on OrderDetails / Business Rules node, and press New Business Rule.

New Business Rule context menu option for Order Details controller in the Project Explorer.

Assign these values:

Property Value
Type C# / Visual Basic
Command Name Calculate
Phase Execute

Press OK to save.

Code business rule files do not exist until the application generator has created them. On Project Designer toolbar, press Browse.

When complete, right-click OrderDetails / Business Rules / Calculate business rule node, and press Edit Rule in Visual Studio.

Edit Rule in Visual Studio context menu option for Code business rule.

The file will be opened in Visual Studio. The entire class definition and parameters of the business rule method are already defined.

Replace the body of the rule with the call of UpdateFieldValue method:

C#:

using System;
using MyCompany.Data;

namespace MyCompany.Rules
{
    public partial class OrderDetailsBusinessRules : MyCompany.Data.BusinessRules
    {
        
        [Rule("r101")]
        public void r101Implementation(int? orderID, 
            string orderCustomerID, string orderCustomerCompanyName, 
            string orderEmployeeLastName, string orderShipViaCompanyName, 
            int? productID, string productProductName, string productCategoryCategoryName, 
            string productSupplierCompanyName, decimal? unitPrice, short? quantity, 
            float? discount, decimal? extendedPrice)
        {
            UpdateFieldValue("ExtendedPrice", 
                Convert.ToDouble(unitPrice.Value) * quantity.Value * (1 - discount.Value));
        }
    }
}

Visual Basic:

Imports MyCompany.Data
Imports System

Namespace MyCompany.Rules

    Partial Public Class OrderDetailsBusinessRules
        Inherits MyCompany.Data.BusinessRules

        <Rule("r101")> _
        Public Sub r101Implementation(
                ByVal orderID As Nullable(Of Integer),
                ByVal orderCustomerID As String,
                ByVal orderCustomerCompanyName As String,
                ByVal orderEmployeeLastName As String,
                ByVal orderShipViaCompanyName As String,
                ByVal productID As Nullable(Of Integer),
                ByVal productProductName As String,
                ByVal productCategoryCategoryName As String,
                ByVal productSupplierCompanyName As String,
                ByVal unitPrice As Nullable(Of Decimal),
                ByVal quantity As Nullable(Of Short),
                ByVal discount As Nullable(Of Single),
                ByVal extendedPrice As Nullable(Of Decimal)
            )
            UpdateFieldValue("ExtendedPrice",
                Convert.ToDouble(unitPrice.Value) * quantity.Value * (1 - discount.Value))
        End Sub
    End Class
End Namespace

Save the file, and refresh the webpage.

The same behavior as with the SQL business rule will be exhibited every time a context field is changed in the form. The client library will make a short trip to the web server to perform the calculation. The application framework will call the business rules class method which is linked to the business rule defined in OrderDetails data controller.

JavaScript Business Rule

If the values of the base fields are known on the client at the time when a calculation needs to be performed, then the web server round-trip is redundant. JavaScript business rules offer an option to implement complex logic executed by the web browser.

First, disable execution of the previously created C#/Visual Basic business rule. Double-click on OrderDetails / Business Rules / Calculate node.

SQL business rule 'Calculate' of OrderDetails controller in the Project Explorer.

Change the Command Name property:

Property Value
Command Name DoNotRun

Press OK to save. Alternatively, business rule r101 can be deleted.

Right-click on OrderDetails / Business Rules node, and press New Business Rule.

New Business Rule context menu option for Order Details controller.

Assign these values:

Property Value
Type JavaScript
Command Name Calculate
Phase Execute
Script
[ExtendedPrice] = [UnitPrice] * [Quantity] * (1 - [Discount]);
this.preventDefault();

At runtime, the client library will automatically translate the script into the following JavaScript code:

this.updateFieldValue('ExtendedPrice', 
    this.selectFieldValue('UnitPrice') * 
    this.selectFieldValue('Quantity') * 
    (1 - this.selectFieldValue('Discount')));
this.preventDefault();

Press OK to save. On the toolbar, press Browse. Open the form view of an order detail.

Order Details form without any changed values.

Change a value in one of the fields. Press Tab to shift focus away from the field. The Extended Price will automatically be updated without performing a server request.

When focus is shifted from a field, the Extended Price will be recalculated.

The call of the method preventDefault() will prevent the client library from processing the Calculate action on the server.

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