Resolving Data Conflicts

[ Team LiB ] Recipe 6.11 Resolving Data Conflicts Problem You need to effectively resolve data conflicts and prevent overwriting of existing data when attempting to update changes in a DataSet to a database where the underlying data has changed.
Nội dung trích xuất từ tài liệu:
Resolving Data Conflicts[ Team LiB ]Recipe 6.11 Resolving Data ConflictsProblemYou need to effectively resolve data conflicts and prevent overwriting of existing datawhen attempting to update changes in a DataSet to a database where the underlying datahas changed.SolutionHandle the DBConcurrencyException within the RowUpdated event of the DataAdapter.The schema of table TBL0611 used in this solution is shown in Table 6-13. Table 6-13. TBL0611 schema Column name Data type Length Allow nulls?Id int 4 NoField1 nvarchar 50 YesThe sample code contains seven event handlers:Form.Load Creates a DataSet A containing a single DataTable A, filling the schema and data for the table from TBL0611 from the database using a DataAdapter. The ContinueUpdateOnError property of the DataAdapter is set to true. A CommandBuilder object is created to generate the updating logic for the DataAdapter. The default view of DataTable A is bound to a data grid on the form. A conflict table is created to store the original row data for a row when a concurrency error is encountered while updating a row from DataTable A back to TBL0611 in the database. A DataAdapter that uses a parameterized SQL SELECT statement to retrieve the original row data is created. The schema for the conflict table is loaded from TBL0611 using the DataAdapter. The default view of the conflict table is bound to a data grid on the form. A DataSet B and a conflict table for DataTable B row update concurrency errors are created in the same way as described for DataSet A.Refresh A Button.Click Clears the conflict table, clears the data in table A, and uses a DataAdapter to fill table A from TBL0611 in the database.Refresh B Button.Click Clears the conflict table, clears the data in table B, and uses a DataAdapter to fill table B from TBL0611 in the database.Update A Button.Click Clears the conflict table and uses a DataAdapter to update changes made to table A back to table TBL0611 in the database.Update B Button.Click Clears the conflict table and uses a DataAdapter to update changes made to table B back to table TBL0611 in the database.A DataAdapter.RowUpdated Checks to see if a concurrency error occurred when updating the row in DataTable A to table TBL0611 in the database. If an error occurred during the deletion of a row, the RejectChanges( ) method is used to cancel the delete. For all rows with a concurrency error, the Id for the row is retrieved from the row and used with the DataAdapter for the conflict table to try to get the original data for the row from the TBL0611 in the database. An error is set on the row in the conflict table indicating whether it was changed (the row in error was retrieved from the database) or deleted (a row in error could not be retrieved from the database).B DataAdapter.RowUpdated Checks to see if a concurrency error occurred when updating the row in DataTable B to table TBL0611 in the database. If an error occurred during the deletion of a row, the RejectChanges( ) method is used to cancel the delete. For all rows with a concurrency error, the Id for the row is retrieved from the row and used with the DataAdapter for the conflict table to try to get the original data for the row from the TBL0611 in the database. An error is set on the row in the conflict table indicating whether it was changed (the row in error was retrieved from the database) or deleted (a row in error could not be retrieved from the database).The C# code is shown in Example 6-29.Example 6-29. File: ResolveDataConflictsForm.cs// Namespaces, variables, and constantsusing System;using System.Configuration;using System.Text;using System.Data;using System.Data.SqlClient;private const String TABLENAME = TBL0611;private SqlDataAdapter daA, daB;private DataSet dsA, dsB;// . . .private void ResolveDataConflictsForm_Load(object sender, System.EventArgs e){ // Tables A and B are filled from the same data source table. String sqlText = SELECT * FROM + TABLENAME; // Create the DataAdapter for table A. daA = new SqlDataAdapter(sqlText, ConfigurationSettings.AppSettings[Sql_SqlAuth_ConnectString]); daA.ContinueUpdateOnError = true; // Handle the RowUpdated event. daA.RowUpdated += new SqlRowUpdatedEventHandler(daA_RowUpdated); // Get the schema and data for table A in the DataSet. dsA = new DataSet(A); daA.FillSchema(dsA, SchemaType.Source, TABLENAME); daA.Fill(dsA, TABLENAME); // Create the command builder. SqlCommandBuilder cbA = new SqlCommandBuilder(daA); // Bind the default view for table A to the grid. dataGridA.DataSource = dsA.Tables[TABLENAME].DefaultView; // Create a DataAdapter to retrieve original rows // for conflicts when updating table A. conflictDaA = new SqlDataAdapter(sqlText + WHERE Id = @Id, ConfigurationSettings.AppSettings[Sql_ConnectString]); conflictDaA.SelectCommand.Parameters.Add(@Id, SqlDbType.Int, 0); // Create a DataSet with the conflict table schema. conflictDsA = new DataSet( ); daA.FillSchema(conflictDsA, SchemaType.Source, TABLENAME); // Bind the default view for conflict table B to the grid. conflictDataGridA.DataSource = conflictDsA.Tables[TABLENAME].DefaultView; // Create the DataAdapter for table B. daB = new SqlDataAdapter(sqlText, ConfigurationSettings.AppSettings[Sql_SqlAuth_ConnectString]); daB.ContinueUpdateOnError = true; // Handle the RowUpdated event. daB.RowUpdated += new SqlRow ...