Tài liệu Finding Rows in a DataTable ppt

Find Button.Click Uses three different techniques—the DataTable.Select method, the DataTable.Rows.Find method, and the DataView.RowFilter property—to find rows in the Orders table matc

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Recipe 3.8 Finding Rows in a DataTable

Problem

You need to find a row or group of rows in a DataTable meeting certain criteria

Solution

Choose from the three techniques shown in the sample code to locate data in the table meeting user-specified criteria

The sample code contains two event handlers:

Form.Load

Sets up the sample by creating a DataTable containing the Orders table from the Northwind sample database The default view of the table is bound to the data grid

on the form

Find Button.Click

Uses three different techniques—the DataTable.Select( ) method, the

DataTable.Rows.Find( ) method, and the DataView.RowFilter property—to find rows in the Orders table matching the user-specified Country

The C# code is shown in Example 3-8

Example 3-8 File: FindDataTableRowsForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Data;

using System.Data.SqlClient;

// Table name constants

private const String ORDERS_TABLE = "Orders";

// Field name constants

private const String ORDERID_FIELD = "OrderID";

private const String SHIPCOUNTRY_FIELD = "ShipCountry";

//

private void FindDataTableRowsForm_Load(object sender, System.EventArgs e) {

// Fill the Orders table

SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Orders",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable dt = new DataTable(ORDERS_TABLE);

da.Fill(dt);

da.FillSchema(dt, SchemaType.Source);

// Bind the table to the grid

dataGrid.DataSource = dt.DefaultView;

}

private void findButton_Click(object sender, System.EventArgs e)

{

// Get the table bound to the grid

DataTable dt = ((DataView)dataGrid.DataSource).Table;

// Build the filter using contents of the text box

String filter = SHIPCOUNTRY_FIELD + " = '" +

shipCountryTextBox.Text + "'";

// Locate the records using the Select( ) method of the DataTable

DataRow[] drc = dt.Select(filter);

resultTextBox.Text = "DataTable.Select returned " + drc.Length +

" record(s)." + Environment.NewLine;

// Iterate over the collection of rows filtered in the previous step

// and find them in the table using the Find( ) method of the

// DataRowCollection for the DataTable

int findCount = 0;

foreach(DataRow row in drc)

{

DataRow foundRow = dt.Rows.Find(row[ORDERID_FIELD]);

if (foundRow != null)

findCount++;

}

resultTextBox.Text += "DataTable.Rows.Find returned " + findCount +

" record(s)." + Environment.NewLine;

// Locate records using the RowFilter property of the DataView

DataView dv = new DataView(dt);

dv.RowFilter = filter;

resultTextBox.Text += "DataView.RowFilter returned " + dv.Count +

" record(s).";

}

Discussion

There are three ways to locate one or more rows in a table:

• Use the Select( ) method of the DataTable to return an array of DataRow objects

matching the specified filter criteria By default, the rows in the array are ordered

by the primary key or, lacking a primary key, by the order in which the rows were added to the table A sort order can be specified in an optional argument The Select( ) method also takes an optional argument that can also be used to select records matching a specified row state from the DataViewRowState enumeration

• Use the Find( ) method of the DataRowCollection of the table to return a row

matching the primary key value or values passed as an object argument or an array

of object arguments, respectively To use the Find( ) method, the DataTable to which the DataRowCollection belongs must have a primary key defined,

otherwise a MissingPrimaryKeyException is raised If the primary key does not exist in the DataRowCollection, the method returns null

• Use a DataView based on the DataTable to locate records in one of the following

ways:

o Use the RowFilter property of the DataView Create a DataView based on the DataTable and set the RowFilter property to a filter expression

o Use the Find( ) method of the DataView to return the index of the row matching the sort key value or values passed as an object argument or an array of object arguments, respectively If the sort key value does not exist

in the DataView, null is returned

o Use the FindRows( ) method of the DataView to return an array of

DataRowView objects whose columns match the specified sort key value

If the sort key value does not exist, an empty DataRowView array is returned

For more information about the Find( ) and FindRows( ) methods of the DataView, see Recipe 3.9

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