Section 16.4. Searching by Category

16.4. Searching by Category

Making a web service method call for each ISBN you want to check is by far not the most efficient approach possible. Not only does it involve multiple round trips to the Amazon service, but it is likely that the ISBNs you list will become out of date almost immediately as new competitors come on the market, and others go out of print.

Fortunately, Amazon can search by category. In the next (and final) iteration of this program, you'll dispense with your XML files with ISBNs and instead simply ask Amazon for all the books in the ASP.NET, C#, and VB.NET categories.

To keep the example simple, you'll use the default of retrieving just 10 books in each category. Amazon Web Services allow a great deal of tailoring of your request, but for this example, we'll go with the minimal properties required.

Create a copy of the SalesRankDBWebServices project and name it AmazonWebServiceClientSearching. You'll modify it as shown in Example 16-5.

Example 16-5. SalesRankDBWebServices02

#region Using directives using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Windows.Forms; #endregion namespace AmazonWebServiceClient {    partial class AmazonWebServiceClient : Form    {       private int timeRemaining;       const int WaitTime = 900; // 15 minutes       private string connectionString;       private System.Data.SqlClient.SqlConnection connection;       private System.Data.SqlClient.SqlCommand command;       public AmazonWebServiceClient( )       {          InitializeComponent( );       }       private void AmazonWebServiceClient_Load( object sender,          EventArgs e )       {          // connection string to connect to the Sales Rank Database          connectionString =       "server=localhost;Trusted_Connection=true;database=AmazonSalesRanks";          // Create connection object, initialize with           // connection string.           connection =             new System.Data.SqlClient.SqlConnection( connectionString );          // Create a SqlCommand object and assign the connection          command =             new System.Data.SqlClient.SqlCommand( );          command.Connection = connection;          timeRemaining = 1;  // when you first start up, get the info.          UpdateButton( );       }       private void btnStart_Click( object sender, EventArgs e )       {          // toggle the timer          updateTimer.Enabled = updateTimer.Enabled ? false : true;          UpdateButton( );       }       private void btnNow_Click( object sender, EventArgs e )       {          timeRemaining = 2;       }       private void UpdateButton( )       {          btnStart.Text = updateTimer.Enabled ? "Stop" : "Start";       }       private void updateTimer_Tick( object sender, EventArgs e )       {          if ( updateTimer.Enabled )             txtClock.Text = ( --timeRemaining ).ToString( ) + " seconds";          else             txtClock.Text = "Stopped";          // hi ho, hi ho, it's off to work we go...          if ( timeRemaining < 1 )          {             timeRemaining = WaitTime;  // reset the clock             timeRemaining = WaitTime;             GetInfoFromAmazon( "ASP.NET", "ASPNET" );             GetInfoFromAmazon( "C#", "CSHARP" );             GetInfoFromAmazon( "VB.NET", "VBNET" );          }       }       private void GetInfoFromAmazon( string keyword, string technology )       {                    AWSProductData productData = new AWSProductData( );          ItemSearch srch = null;          try          {             ItemSearchRequest req = new ItemSearchRequest( );             req.Keywords = keyword;             req.SearchIndex = "Books";             srch = new ItemSearch( );             srch.AssociateTag = "libertyassocia00A";              srch.SubscriptionId = " Your Subscription ID ";             srch.Request = new ItemSearchRequest[1];             srch.Request[0] = req;          }          catch ( System.Exception e )          {             lblStatus.Text = e.Message;          }          ItemSearchResponse response;          int salesRank = -1;          string isbn = string.Empty;          string author = string.Empty;          string pubDate = string.Empty;           string publisher = string.Empty;           string title = string.Empty;           string strURL = string.Empty;          Items[] responseItems = null;          try          {             // get back ItemSearchResponse             response = productData.ItemSearch( srch );             // Items returns array of Items             responseItems = response.Items;             foreach ( Items items in responseItems )             {                // Item property of Items is an array of Item objects                Item[] arrayOfItem = items.Item;                           foreach ( Item item in arrayOfItem )                {                   isbn = FixQuotes( item.ItemAttributes.ISBN );                   salesRank = item.SalesRank ==                       null ? -1 : Convert.ToInt32( item.SalesRank );                   author = FixQuotes( item.ItemAttributes.Author[0] );                   pubDate = FixQuotes(                        item.ItemAttributes.PublicationDate);                   publisher = FixQuotes( item.ItemAttributes.Publisher );                   title = FixQuotes( item.ItemAttributes.Title );                   strURL = item.DetailPageURL;                   // update the list box                   string results = title + " by " + author + ": " +                      publisher + ", " + pubDate + ". Rank: " + salesRank;                   lbOutput.Items.Add( results );                   lbOutput.SelectedIndex = lbOutput.Items.Count - 1;                   // update the database                   string commandString = @"Update BookInfo set isbn = '" +                      isbn + "', title = '" + title + "', publisher = '" +                      publisher + "', pubDate = '" +                       pubDate + "', rank = " +                      salesRank + ", link = '" +                       strURL + "', lastUpdate = '" +                      System.DateTime.Now + "', technology = '" +                      technology + "', author = '" +                      author + "' where isbn = '" +                      isbn + "'";                   command.CommandText = commandString;                   try                   {                      // if no rows were affected, this is a new record                      connection.Open( );                      int numRowsAffected = command.ExecuteNonQuery( );                      if ( numRowsAffected == 0 )                      {                         commandString = @"Insert into BookInfo values ('" +                            isbn + "', '" + title + "', '" + publisher +                             "', '" +                            pubDate + "', '" + FixQuotes( strURL ) + "', "                             + salesRank + ", '" +                            System.DateTime.Now +                            "', '" + technology + "', '" + author + "')";                         command.CommandText = commandString;                         command.ExecuteNonQuery( );                      }                   }                   catch ( Exception ex )                   {                      lblStatus.Text = ex.Message;                      lbOutput.Items.Add( "Unable to update database!" );                      lbOutput.SelectedIndex = lbOutput.Items.Count - 1;                   }                   finally                   {                      connection.Close( );      // clean up                   }                   Application.DoEvents( );      // update the UI                }             }          }          catch ( System.Exception ex)          {             lblStatus.Text = ex.Message;          }       }     // close for GetInfoFromAmazon       private string FixQuotes( string s )       {          if ( s == null )             return string.Empty;          return s.Replace( "'", "''" );       }    } // end class } // end name space

In this version, all the code to manipulate the XML files is removed. The method GetInfoFromISBN is replaced by GetInfoFromAmazon. Instead of creating an ItemLookupRequest object, you create a KeywordRequest object:

private void GetInfoFromAmazon( string keyword, string technology ) {        AWSProductData productData = new AWSProductData( );    ItemSearch srch = null;    try    {       ItemSearchRequest req = new ItemSearchRequest( );       req.Keywords = keyword;       req.SearchIndex = "Books";       srch = new ItemSearch( );       srch.AssociateTag = "libertyassocia00A";        srch.SubscriptionId = "Your Subscription ID";       srch.Request = new ItemSearchRequest[1];       srch.Request[0] = req;    }

Notice that the keyword property has been assigned the keyword parameter passed in (i.e., C#, ASP.NET, or VB.NET). The SearchIndex property limits the search to books (rather than, for example, records).

Once the ItemSearchRequest object is created, you embed it in an ItemSearch object that holds the AssociateTag and the SubscriptionID.

What you get back is an ItemSearchResponse object. The Items property of this object is an array of Item objects. Each Item object has an Item property which, not surprisingly, is an array of Item objects. It is in these Item objects that you'll find the information about the matching books.