9.5 Using Row Version Information

ADO.NET maintains up to three versions of each DataRow object. The DataAdapter reconciles changes made since the data was loaded from the data source, thereby making changes to the disconnected data permanent. Two versions of each row are maintained to allow the DataAdapter to determine how to perform the reconciliation. The Original version contains the values that were loaded into the row. The Current version contains the latest version of the data, including the changes made since the data was originally loaded. The Original version isn't available for newly created rows.

ADO.NET also allows a row to be put into edit mode which temporarily suspends events for the row and allows the user to make multiple changes to the row without triggering validation rules. The BeginEdit( ) method of the DataRow puts the row into edit mode, while the EndEdit( ) and CancelEdit( ) methods take the row out of edit mode. AcceptChanges( ) also takes the row out of edit mode because it implicitly calls EndEdit( ) , as does RejectChanges( ) , which implicitly calls CancelEdit( ) .

A Proposed row version is made available while the row is in edit mode and contains the changes that have been made to the row while it was in edit mode. If the EndEdit( ) method is called, the changes made are copied from the Proposed row to the Current row. If the CancelEdit( ) method is called, the values in the Proposed version are simply discarded. In either case, once the editing is completed, the Proposed version of the row is no longer available.

Finally, a Default row version returns the Current version if the row isn't being edited or the Proposed row if it is.

The HasVersion( ) method of the DataRow can determine whether a specific version of the row exists. If the version exists, column values for it can be retrieved using one of the three overloads of the DataRow indexer. The following example shows how to check for and retrieve the Proposed version of a row:

 DataRow dr; // ... code to build, fill, and modify the row object objColVal; // check if the Proposed version of the row exists if (dr.HasVersion(DataRowVersion.Proposed)) {     // retrieve the value for the first column in the Proposed row     objColVal = dr[0, DataRowVersion.Proposed]; }