Assembly: System.Web (in System.Web.dll)
The format string is applied only to primary keys, such as those that are identified by the DataKeyNames property of the associated data-bound control, or in delete and update scenarios where the ConflictDetection property is set to the CompareAllValues value and a set of oldValues are passed to the corresponding data method. In this case, the format string is applied to each parameter name in the oldValues collection.
Two common scenarios where you might change the property are as follows:
To differentiate between old and new values in updates. When the ConflictDetection property is set to the CompareAllValues value, parameters for both the original and new values are added to the UpdateParameters collection. Without the formatting string, two parameters with the same name would be created for each data field. By changing the name of the original value parameter, you can compare the data to the original data source to detect conflicts and compare key values.
Some visual designers implement a particular naming scheme for original values and keys.