Tài liệu Finding DataRowView Objects in a DataView docx

Finding DataRowView Objects in a DataView You can find the index of a DataRowView in a DataView using the Find() method of a DataView. You can also get an array of DataRowView objects using the FindRows() method of a DataView. You'll learn how to use the Find() and FindRows() methods in this section. Finding the Index of a DataRowView Using the Find() Method The Find() method returns the index of the DataRowView with the specified primary key in your DataView. The int returned by this method is the index of the DataRowView if found; otherwise -1 is returned. To find the correct index, you must first set the Sort property of your DataView to sort on the primary key. For example, if you want to find a DataRowView based on the CustomerID, you must set the Sort property of your DataView to CustomerID, CustomerID ASC, or CustomerID DESC: string sortExpression = "CustomerID"; customersDV.Sort = sortExpression; Assume that the sorted DataRowView objects in customersDV are as follows: AROUT Around the Horn UK BSBEV B's Beverages UK CONSH Consolidated Holdings UK EASTC Eastern Connection UK ISLAT Island Trading UK NORTS North/South UK SEVES Seven Seas Imports UK The following example calls the Find() method to find the index of the DataRowView in customersDV with a CustomerID of BSBEV: int index = customersDV.Find("BSBEV"); Because BSBEV occurs at index 1, the Find() method returns 1. Note DataRowView objects in a DataView start at index 0. Therefore, BSBEV occurs at index 1. Finding DataRowView Objects Using the FindRows() Method The FindRows() method of a DataView finds and returns an array of DataRowView objects for which the primary key column matches the primary key in your DataView. If no rows were found, then the returned array will have zero elements, and the Length property of the array will be 0. To find DataRowView objects using the FindRows() method, you must first set the Sort property of your DataView to sort on the primary key. For example, if you want to find DataRowView objects based on the CustomerID, you must set the Sort property of your DataView to CustomerID, CustomerID ASC, or CustomerID DESC: string sortExpression = "CustomerID"; customersDV.Sort = sortExpression; The following example calls the FindRows() method to find the DataRowView that has the CustomerID of BSBEV: DataRowView[] customersDRVs = customersDV.FindRows("BSBEV"); Since there is only one match, the customersDRVs array will contain one DataRowView. Listing 13.2 shows a program that uses the Find() and FindRows() methods. Listing 13.2: FINDINGDATAROWVIEWS.CS /* FindingDataRowViews.cs illustrates the use of the Find() and FindRows() methods of a DataView to find DataRowView objects */ using System; using System.Data; using System.Data.SqlClient; class FindingDataRowViews { public static void Main() { SqlConnection mySqlConnection = new SqlConnection( "server=localhost;database=Northwind;uid=sa;pwd=sa" ); SqlCommand mySqlCommand = mySqlConnection.CreateCommand(); mySqlCommand.CommandText = "SELECT CustomerID, CompanyName, Country " + "FROM Customers"; SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter(); mySqlDataAdapter.SelectCommand = mySqlCommand; DataSet myDataSet = new DataSet(); mySqlConnection.Open(); mySqlDataAdapter.Fill(myDataSet, "Customers"); mySqlConnection.Close(); DataTable customersDT = myDataSet.Tables["Customers"]; // set up the filter and sort expressions string filterExpression = "Country = 'UK'"; string sortExpression = "CustomerID"; DataViewRowState rowStateFilter = DataViewRowState.OriginalRows; // create a DataView object named customersDV DataView customersDV = new DataView(); customersDV.Table = customersDT; customersDV.RowFilter = filterExpression; customersDV.Sort = sortExpression; customersDV.RowStateFilter = rowStateFilter; // display the rows in the customersDV DataView object foreach (DataRowView myDataRowView in customersDV) { for (int count = 0; count < customersDV.Table.Columns.Count; count++) { Console.WriteLine(myDataRowView[count]); } Console.WriteLine(""); } // use the Find() method of customersDV to find the index of // the DataRowView whose CustomerID is BSBEV int index = customersDV.Find("BSBEV"); Console.WriteLine("BSBEV found at index " + index + "\n"); // use the FindRows() method of customersDV to find the DataRowView // whose CustomerID is BSBEV DataRowView[] customersDRVs = customersDV.FindRows("BSBEV"); foreach (DataRowView myDataRowView in customersDRVs) { for (int count = 0; count < customersDV.Table.Columns.Count; count++) { Console.WriteLine(myDataRowView[count]); } Console.WriteLine(""); } } } Tip If you are using an early version of the .NET SDK, you might encounter the following compilation error when compiling this program: FindingDataRowViews.cs(59,35): error CS0117: 'System.Data.DataView' does not contain a definition for 'FindRows' If you get this error, compile the program with Visual Studio .NET. The output from this program is as follows: AROUT Around the Horn UK BSBEV B's Beverages UK CONSH Consolidated Holdings UK EASTC Eastern Connection UK ISLAT Island Trading UK NORTS North/South UK SEVES Seven Seas Imports UK BSBEV found at index 1 BSBEV B's Beverages UK . Finding DataRowView Objects in a DataView You can find the index of a DataRowView in a DataView using the Find() method of a DataView. You can also. Listing 13.2: FINDINGDATAROWVIEWS.CS /* FindingDataRowViews.cs illustrates the use of the Find() and FindRows() methods of a DataView to find DataRowView