The update is performed on a by-row basis. For every inserted, modified, and deleted row, the DataAdapter.Update(System.Data.DataSet) method determines the type of change that has been performed on it (Insert, Update or Delete). Depending on the type of change, the Insert, Update, or Delete command template executes to propagate the modified row to the data source. When an application calls the DataAdapter.Update(System.Data.DataSet) method, the System.Data.Common.DataAdapter examines the System.Data.DataRow.RowState property, and executes the required INSERT, UPDATE, or DELETE statements iteratively for each row, based on the order of the indexes configured in the System.Data.DataSet. For example, DataAdapter.Update(System.Data.DataSet) might execute a DELETE statement, followed by an INSERT statement, and then another DELETE statement, due to the ordering of the rows in the System.Data.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 System.Data.DataSet.GetChanges method in situations where you must control the sequence of statement types (for example, INSERT before UPDATE). For more information, see Updating the Database with a DataAdapter and the DataSet.

If INSERT, UPDATE, or DELETE statements have not been specified, the DataAdapter.Update(System.Data.DataSet) method generates an exception. However, you can create a System.Data.SqlClient.SqlCommandBuilder or System.Data.OleDb.OleDbCommandBuilder object to automatically generate SQL statements for single-table updates if you set the SelectCommand property of a .NET Framework 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 System.Data.DataSet. For more information see Automatically Generated Commands.

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

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

When using DataAdapter.Update(System.Data.DataSet), the order of execution is as follows:

[The 'ordered' type of list has not been implemented in the ECMA stylesheet.]

Each command associated with the System.Data.Common.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 System.Data.DataTable column that the System.Data.Common.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 nonexistent column, the action taken depends on one of the following System.Data.MissingMappingAction values.

MissingMappingAction.Passthrough	Use the source column names and table names in the System.Data.DataSet if no mapping is present.
MissingMappingAction.Ignore	A SystemException is generated. When the mappings are explicitly set, a missing mapping for an input parameter is usually the result of an error.
MissingMappingAction.Error	A SystemException is generated.

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 nonexistent 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.

Calling the System.Data.DataSet.AcceptChanges method or System.Data.DataTable.AcceptChanges method will commit all changes in the System.Data.DataSet or System.Data.DataTable. If either of these methods are called before the DbDataAdapter.Update(System.Data.DataSet) method is called, no changes will be committed when the DbDataAdapter.Update(System.Data.DataSet) method is called, unless further changes have been made since System.Data.DataSet.AcceptChanges or System.Data.DataTable.AcceptChanges was called.

Namespace: System.Data.Common
Assembly: System.Data (in System.Data.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0