System.Data.Common Namespace   DataAdapter Class

Calls the respective INSERT, UPDATE, or DELETE statements for each inserted, updated, or deleted row in the specified DataSet.

[ VB ]
MustOverride Public Function Update ( _
   ByVal dataSet As DataSet _
) As Integer

[ C# ]
public abstract int Update (
   DataSet dataSet
);

[ C++ ]
public: virtual int Update (
   DataSet* dataSet
 ) = 0;

[ JScript ]
public abstract function Update (
   dataSet : DataSet
) : int;

dataSet

The DataSet used to update the data source.

The number of rows successfully updated from the DataSet.

When an application calls the Update method, the DataAdapter examines the RowState property, and executes the required INSERT, UPDATE, or DELETE statements based on the order of the indexes configured in the DataSet. For example, Update might execute a DELETE statement, followed by an INSERT statement, and then another DELETE statement, due to the ordering of the rows in the DataTable.

It should be noted that these statements are not performed as a batch process; each row is updated individually. An application can call the GetChanges method in situations where you must control the sequence of statement types ( for example, INSERTs before UPDATEs ). For more information, see Updating the Database with a DataAdapter and the DataSet.

If INSERT, UPDATE, or DELETE statements have not been specified, the Update method generates an exception. However, you can create a SqlCommandBuilder or OleDbCommandBuilder object to automatically generate SQL statements for single-table updates if you set the SelectCommand property of a .NET data provider. Then, any additional SQL statements that you do not set are generated by the CommandBuilder. This generation logic requires key column information to be present in the DataSet. For more information see Automatically Generated Commands.

The Update method retrieves rows from the table listed in the first mapping before performing an update. The Update then refreshes the row using the value of the UpdatedRowSource property. Any additional rows returned are ignored.

After any data is loaded back into the DataSet, the OnRowUpdated event is raised, allowing the user to inspect the reconciled DataSet row and any output parameters returned by the command. After a row updates successfully, the changes to that row are accepted.

When using Update, the order of execution is as follows:

1. The values in the DataRow are moved to the parameter values.
2. The OnRowUpdating event is raised.
3. The command executes.
4. If the command is set to FirstReturnedRecord, then the first returned result is placed in the DataRow.
5. If there are output parameters, they are placed in the DataRow.
6. The OnRowUpdated event is raised.
7. AcceptChanges is called.

Each command associated with the DataAdapter usually has a parameters collection associated with it. Parameters are mapped to the current row through the SourceColumn and SourceVersion properties of a .NET data provider's Parameter class. SourceColumn refers to a DataTable column that the DataAdapter references to obtain parameter values for the current row.

SourceColumn refers to the unmapped column name before any table mappings have been applied. If SourceColumn refers to a non-existent column, the action taken depends on one of the following MissingMappingAction values.

The SourceColumn property is also used to map the value for output or input/output parameters back to the DataSet. An exception is generated if it refers to a non-existent column.

The SourceVersion property of a .NET data provider's Parameter class determines whether to use the Original, Current, or Proposed version of the column value. This capability is often used to include original values in the WHERE clause of an UPDATE statement to check for optimistic concurrency violations.

The following example uses the derived OleDbDataAdapter class to Update the data source.

public DataSet updateData ( DataSet myDataSet, 
      string connString, string query ) {
   OleDbConnection myConn = new OleDbConnection ( connString );
   OleDbDataAdapter adapter = new OleDbDataAdapter ( );
   adapter.SelectCommand = new OleDbCommand ( query, myConn );
   OleDbCommandBuilder custCB = new OleDbCommandBuilder ( adapter );
   DataSet myDataSet = new DataSet ( );

   myConn.Open ( );
   adapter.Fill ( myDataSet );

   // ... code to modify data in dataset here ...

   // without the OleDbCommandBuilder this line would fail
   adapter.Update ( myDataSet );

   myConn.Close ( );
   return myDataSet;
}

Public Function updateData ( myDataSet As DataSet, _
      connString As String, query As String )
   Dim myConn As New OleDbConnection ( connString )
   Dim adapter As New OleDbDataAdapter ( )
   adapter.SelectCommand = New OleDbCommand ( query, myConn )
   Dim custCB As New OleDbCommandBuilder ( adapter )
   Dim myDataSet As DataSet = New DataSet

   myConn.Open ( )
   adapter.Fill ( myDataSet )

   ' ... code to modify data in DataSet here ...

   ' without the OleDbCommandBuilder this line would fail.
   adapter.Update ( myDataSet )

   myConn.Close ( )
   updateData = myDataSet
End Function

DataAdapter Members