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