The ObjectDataSourceView.OldValuesParameterFormatString format string is applied to primary keys only, such as those that are identified with the DataKeyNames property of a data-bound control or in delete and update scenarios, where the ObjectDataSourceView.ConflictDetection property is set to the System.Web.UI.ConflictOptions.CompareAllValues value and the set of original values that are passed to the corresponding data method.

Two common scenarios where you might change the ObjectDataSourceView.OldValuesParameterFormatString property are as follows:

• To differentiate between old and new values in updates. When the ObjectDataSourceView.ConflictDetection property is set to the System.Web.UI.ConflictOptions.CompareAllValues value, parameters for both the original and new values are added to the ObjectDataSource.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.

The value of the ObjectDataSourceView.OldValuesParameterFormatString is stored in view state.