12.3 Accessing Data Through a DataView

A DataView isn't just for data binding. You can also use it when making programmatic changes. For example, you might create a DataView that contains rows that match certain criteria and then apply a global change to these rows. For example, the following code creates a view that includes all rows with a null value in the Country field and then deletes them:

 // Find all the rows where a Country isn't specified. DataView view = new DataView(ds.Tables["Customers"]); view.RowFilter = "Country IS NULL"; // Delete these rows. foreach (DataRowView row in view) {     row.Delete(); } // Display the results. dataGrid1.DataSource = ds.Tables["Customers"].DefaultView; 

This example uses the indexer for the DataView , which accesses the collection of DataRowView objects. Each DataRowView represents a single row from the original DataTable . The DataRowView provides most of the same features as the underlying DataRow object, including the ability to begin and end editing, access values using the field name , and delete the row. You can also access the underlying DataRow directly through the DataRowView.Row property.

12.3.1 Searching a DataView

Once you have defined a sort order for a DataView , either by setting the RowFilter or the ApplyDefaultSort properties, you can use criteria to search for rows. The DataView provides two methods for this task: Find( ) and FindRows( ) .

For example, if you have a sort defined on the ContactName column of the Customers table, you can use the Find( ) method to search for a row with the ContactName Roland Mendel. If a match is found, Find( ) returns the index number of the row in the DataView . If no match is found, it returns -1.

 DataView view = new DataView(ds.Tables["Customers"]); view.Sort = "ContactName"; int rowIndex = view.Find("Roland Mendel"); if (rowIndex == -1) {     Console.WriteLine("No match found."); } else {     Console.WriteLine(view[rowIndex]["CustomerID"].ToString() +                        " is a match."); } 

The only limitation is that the string you use to search must match the sort fields exactly. The Find( ) and FindRows( ) methods don't support partial matches or wildcards (in the previous example, you can't search for just "Roland").

If there is a possibility that more than one row will match the criteria you use, you should use the FindRows( ) method instead of Find( ) . It returns an array of DataRowView objects that reference the matching rows. If no match is found, FindRows( ) returns an empty array.

 DataView view = new DataView(ds.Tables["Customers"]); view.Sort = "Country"; DataRowView[] rows = view.FindRows("Germany"); if rows.Length == 0 {     Console.WriteLine("No match found."); } else {     foreach (DataRowView row in rows)     {         Console.WriteLine(row["CustomerID"].ToString() + " is a match.");     } } 

Finally, if you've created a sort expression that incorporates information from multiple columns , you must use an overloaded version of the Find( ) or FindRows( ) methods that accepts an array with search values for all columns, in the same order:

 DataView view = new DataView(ds.Tables["Customers"]); view.Sort = "Country, City"; DataRowView[] rows = view.FindRows(new object[] {"Germany", "Berlin"}; 

The case-sensitivity of search values for the Find( ) and FindRows( ) methods is determined by the CaseSensitive property of the underlying DataTable .

12.3.2 Navigating Relations with a DataView

Unlike the DataRow object, the DataRowView doesn't include methods such as GetChildRows( ) and GetParentRow( ) . However, you can still use DataRelations with the DataView , thanks to the CreateChildView( ) method. CreateChildView( ) accepts a reference to a DataRelation object and creates a new DataView that contains the appropriate child rows.

 // Define a DataRelation. DataColumn parentCol = ds.Tables["Categories"].Columns["CategoryID"]; DataColumn childCol = ds.Tables["Products"].Columns["CategoryID"]; DataRelation relation = new DataRelation("Cat_Prod", parentCol, childCol); ds.Relations.Add(relation); // Create a view on the Categories table. DataView viewCategories = new DataView(ds.Tables["Categories"]); view.Sort = "CategoryName"; // Select a specific category row through the DataRowView. DataRowView rowCategory = viewCategories.Find("Beverages"); // Find products in this category using a new DataView. DataView viewProducts = rowCategory.CreateChildView(relation); // Display the products. foreach (DataRowView row in viewProducts) {     Console.WriteLine(row["ProductName"]); } 

This navigation works in one direction only. There is no direct way to retrieve a reference to the parent row of a DataRowView .



ADO. NET in a Nutshell
ADO.NET in a Nutshell
ISBN: 0596003617
EAN: 2147483647
Year: 2005
Pages: 415

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