Saving Master-Details form using XML

CREATE TABLE Purchase (
	InvoiceID numeric(18, 0) NOT NULL IDENTITY (1, 1),
	InvoiceDate datetime NOT NULL,
	SupplierName varchar(50) NULL
) 
GO

CREATE TABLE PurchaseDetails (
	InvoiceID int NOT NULL ,
	[Description] varchar (75) NOT NULL ,
	Quantity int NOT NULL ,
	Rate numeric(18, 2) NOT NULL ,
	Amount numeric(18, 2) NOT NULL 
)
GO
CREATE PROC InsertPurchaseOrder (@InvoiceDate DATETIME, @SupplierName VARCHAR(50), @PurchaseDetails NTEXT)
AS
BEGIN
 	DECLARE @InvoiceID INT
 	DECLARE @idoc INT

	INSERT INTO Purchase( InvoiceDate, SupplierName)
 	VALUES (@InvoiceDate, @SupplierName)

 	SET @InvoiceID = @@IDENTITY

	-- Create an internal representation of the XML document.
	EXEC sp_xml_preparedocument @idoc OUTPUT, @PurchaseDetails
	-- Insert the values in the details table
	INSERT PurchaseDetails (InvoiceID, [Description], Quantity, Rate, Amount)
	SELECT @InvoiceID, [Description], Quantity, Rate, Amount
	FROM OPENXML (@idoc, '/PurchaseOrder/Details', 2)
	WITH PurchaseDetails
	-- Destory the internal representation of the XML document.
	EXEC sp_xml_removedocument @idoc
END

GO