Tuesday, June 19, 2012

Value Conversion

Project requirements may dictate that conversion should be performed on field values.

For example, the Customer# field of the Customers table in the Northwind database may need to be converted to uppercase.

Customer# field value is uppercase.

However, there is no mechanism preventing users from saving lowercase letters in the field.

Customer# field has no validation to prevent lowercase letters.

Let’s create an SQL Business Rule to perform field value conversion.

Validate on Insert or Update

Start the Project Designer. In the Project Explorer, switch to the Controllers tab. Right-click on Customers / Business Rules node, and select New Business Rule.

New Business Rule for Customers controller.

Use the following properties:

Property Value
Command Name Insert|Update
Type SQL
Phase Before
Script
set @CustomerID = UPPER(@CustomerID)

Press OK to save the business rule. On the toolbar, press Browse.

Navigate to the Customers page, and edit a record. Insert some mixed-case letters in the Customer# field.

Value of Customer# with lowercase letters.

Save the record. The field value will be converted to uppercase.

Value of Customer# has been converted to uppercase.

Validate on Calculate

You can also perform just-in-time value conversion, when the user moves focus away from the field.

Switch back to the Project Designer. In the Project Explorer, double-click on Customers / Business Rule / Insert|Update node.

InsertUpdate business rule for Customers controller.

Change the Command Name property:

Property New Value
Command Name Calculate

Press OK to save the business rule. In order for the calculation to be performed, the field needs to cause a server request.

In the Project Explorer, double-click on Customers / Fields / CustomerID field node.

CustomerID field of Customers controller.

Make the following changes:

Property New Value
The value of this field is calculated by a business rule expression. True
Context Fields CustomerID

Press OK to save the field. On the toolbar, press Browse.

On the Customers page, edit a record. Insert mixed-case characters into the Customer# field.

Lower case characters inserted into CustomerID field.

Press Tab on your keyboard or click on another field. The client library will convert the value in Customer# field into uppercase.

CustomerID value converted to uppercase.

Expanding the Business Rule

The user may still click on the OK button and save the lowercase characters in the field. Therefore, you may need to combine both Insert|Update and Calculate command handling. The following Command Name will cover all possible methods of changing the field.

Property New Value
Command Name Calculate|Insert|Update

The same business logic can be implemented with the help of C#/Visual Basic Business Rules.

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