Tài liệu Navigating Between Parent and Child Records Using a DataRelation pptx

[ Team LiB ]Recipe 3.4 Navigating Between Parent and Child Records Using a DataRelation Problem You want to navigate between the parent and child records in a hierarchical DataSet.. Sol

[ Team LiB ]

Recipe 3.4 Navigating Between Parent and Child Records Using a DataRelation Problem

You want to navigate between the parent and child records in a hierarchical DataSet

Solution

Use a DataRelation to find the child rows for a parent row in a related table, or to find the parent row for a child row in a related table

The sample code starts by creating a DataSet containing the Orders and Order Details tables from the Northwind sample database and a relation between them The code then iterates over the Orders and uses the relation to return all Order Detail rows for each order Finally, the sample code retrieves the CustomerID field from the parent row and displays it for each child

The C# code is shown in Example 3-4

Example 3-4 File: NavigateDataRelationForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Text;

using System.Data;

using System.Data.SqlClient;

// Table name constants

private const String ORDERS_TABLE = "Orders";

private const String ORDERDETAILS_TABLE = "OrderDetails";

// Relation name constants

private const String ORDERS_ORDERDETAILS_RELATION =

"Orders_OrderDetails_Relation";

// Field name constants

private const String ORDERID_FIELD = "OrderID";

private const String PRODUCTID_FIELD = "ProductID";

private const String QUANTITY_FIELD = "Quantity";

private const String CUSTOMERID_FIELD = "CustomerID";

//

DataSet ds = new DataSet( );

SqlDataAdapter da;

// Fill the Order table and add it to the DataSet

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

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable orderTable = new DataTable(ORDERS_TABLE);

da.Fill(orderTable);

ds.Tables.Add(orderTable);

// Fill the OrderDetails table and add it to the DataSet

da = new SqlDataAdapter("SELECT * FROM [Order Details]",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable orderDetailTable = new DataTable(ORDERDETAILS_TABLE);

da.Fill(orderDetailTable);

ds.Tables.Add(orderDetailTable);

// Create a relation between the tables

ds.Relations.Add(ORDERS_ORDERDETAILS_RELATION,

ds.Tables[ORDERS_TABLE].Columns[ORDERID_FIELD],

ds.Tables[ORDERDETAILS_TABLE].Columns[ORDERID_FIELD],

true);

StringBuilder result = new StringBuilder( );

// Iterate over the first 10 order records

for (int i = 0; i < 10; i++)

{

// Display data from the Order record

result.Append("Order ID:" + orderTable.Rows[i][ORDERID_FIELD] +

Environment.NewLine);

// Iterate over the OrderDetails records for the Order

foreach(DataRow row in

orderTable.Rows[i].GetChildRows(ORDERS_ORDERDETAILS_RELATION)) {

// Display data for the OrderDetails record

result.Append("\tProduct: " + row[PRODUCTID_FIELD] +

"; Quantity: " + row[QUANTITY_FIELD] +

// Retrieve CustomerID from the parent Orders record

"; Customer ID: " + row.GetParentRow

(ORDERS_ORDERDETAILS_RELATION)[CUSTOMERID_FIELD] +

Environment.NewLine);

}

result.Append(Environment.NewLine);

}

resultTextBox.Text = result.ToString( );

Discussion

The GetChildRows( ) method of a row in the parent table returns the child rows as an array of DataRow objects for a specified DataRelation The method takes an optional second argument that you can use to specify the version of the data to retrieve as one of the DataRowVersion enumeration values: Current, Default, Original, or Proposed

Similarly, the GetParentRow( ) method of a row in the child table returns the parent row

as a DataRow object for a specified DataRelation Again, an optional second argument allows a specific version of the data to be returned

The GetParentRows( ) method can also be called on a row in the child table to return parent rows in situations where the child row can have multiple parents This method returns an array of DataRow objects Few commercial database products support many-to-many relationships between parent and child records Many-many-to-many relationships are decomposed into two one-to-many relationships through an intermediate table in

relational database management systems (RDBMS)

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