ADO.NET: Using a Collection Class

After establishing a connection to a database, you can use a command to specify the type of operation you want to perform, such as selecting records from the columns of a table, optionally using a condition. To get the data produced by the command, we saw that you could either use a data reader or a data adapter. If you use a data adapter, you can retrieve the values from the data adapter and store them in a data set object:

This is where, once again, a data set object becomes (very) valuable. Remember that a data set object contains one or more tables. Once you can identify a table from a data set, you can create a class that shares its structure. Then use the data from that table and temporarily store it in a collection-based class:

Once the data is available in a collection class, you can manipulate it using a regular class you would have created. This allows you to use your knowledge of collections to explore a database.

1. Create a new Windows Application named CollegeParkAutoParts3
2. In the Solution Explorer, right-click Form1.cs and click Rename
3. Type CollegeParkAutoParts.cs and press Enter
4. Double-click the middle of the form and write code as follows:
   

   using System;
   using System.Collections.Generic;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Linq;
   using System.Text;
   using System.Windows.Forms;
   using System.Data.SqlClient;
   
   namespace CollegeParkAutoParts3
   {
       public partial class CollegeParkAutoParts : Form
       {
           public CollegeParkAutoParts()
           {
               InitializeComponent();
           }
   
           void CreateDatabase()
           {
               using (SqlConnection cnnCPAP =
                   new SqlConnection("Data Source=(local);" +
                                     "Integrated Security=SSPI;"))
               {
                   SqlCommand cmdCPAP = 
   		    new SqlCommand("CREATE DATABASE CollegeParkAutoParts1;", cnnCPAP);
                   cnnCPAP.Open();
   
                   cmdCPAP.ExecuteNonQuery();
                   MessageBox.Show(
   		  "A database named CollegeParkAutoParts has been created.");
               }
   
               using (SqlConnection cnnCPAP =
                   new SqlConnection("Data Source=(local);" +
                                     "Database=CollegeParkAutoParts1;" +
                                     "Integrated Security=SSPI;"))
               {
                   string strCreate = "CREATE TABLE AutoParts(" +
                                      "PartNumber int identity(100001, 1) NOT NULL, " +
                                      "CarYear int, " +
                                      "Make varchar(50), " +
                                      "Model varchar(50), " +
                                      "Category varchar(50), " +
                                      "PartName varchar(100), " +
                                      "UnitPrice money, " +
                                      "CONSTRAINT PK_AutoParts PRIMARY " +
                                      "    KEY (PartNumber));";
                   SqlCommand cmdCPAP = new SqlCommand(strCreate, cnnCPAP);
                   cnnCPAP.Open();
   
                   cmdCPAP.ExecuteNonQuery();
                   MessageBox.Show("A table named Parts has been created.");
               }
   
               using (SqlConnection cnnCPAP =
                   new SqlConnection("Data Source=(local);" +
                                     "Database=CollegeParkAutoParts1;" +
                                     "Integrated Security=SSPI;"))
               {
                   string strCreate = "CREATE TABLE CustomersOrders(" +
                                      "CustomerOrderID int identity(1001, 1) NOT NULL, " +
                                      "ReceiptNumber int NOT NULL, " +
                                      "PartNumber int NULL, " +
                                      "PartName varchar(100), " +
                                      "UnitPrice money, " +
                                      "Quantity int, " +
                                      "SubTotal money, " +
   				   "PartsTotal money, " +
   				   "TaxRate decimal(6, 2), " +
   				   "TaxAmount money, " +
   				   "OrderTotal money, " +
                                      "CONSTRAINT PK_CustomersOrderts PRIMARY " +
                                      "    KEY (CustomerOrderID));";
                   SqlCommand cmdCPAP = new SqlCommand(strCreate, cnnCPAP);
                   cnnCPAP.Open();
   
                   cmdCPAP.ExecuteNonQuery();
                   MessageBox.Show("A table named Parts has been created.");
               }
           }
   
           private void CollegeParkAutoParts_Load(object sender, EventArgs e)
           {
               CreateDatabase();
           }
       }
   }

5. Execute the application to create the database
6. Close the form and return to your programming environment
7. To create a dialog box, on the main menu, click Project -> Add Windows Form...
8. Set the name to MakeEditor and click Add
9. Design the form as follows:
    

   Control Text Name Other Properties Label &Make:     TextBox   txtMake Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
   Form Property	Value
   FormBorderStyle	FixedDialog
   Text	Make Editor
   StartPosition	CenterScreen
   AcceptButton	btnOK
   CancelButton	btnCancel
   MaximizeBox	False
   MinimizeBox	False
   ShowInTaskbar	False

10. To create a dialog box, on the main menu, click Project -> Add Windows Form...
11. Set the name to ModelEditor and click Add
12. Design the form as follows:
     

    Control Text Name Other Properties Label &Model:     TextBox   txtModel Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
    Form Property	Value
    FormBorderStyle	FixedDialog
    Text	Model Editor
    StartPosition	CenterScreen
    AcceptButton	btnOK
    CancelButton	btnCancel
    MaximizeBox	False
    MinimizeBox	False
    ShowInTaskbar	False

13. To create a dialog box, in the Solution Explorer, right-click CollegeParkAutoParts3 -> Add -> Windows Form...
14. Set the name to CategoryEditor and click Add
15. Design the form as follows:
     

    Control Text Name Other Properties Label &Category:     TextBox   txtCategory Modifiers: Public Button OK btnOK DialogResult: OK Button Cancel btnCancel DialogResult: Cancel
    Form Property	Value
    FormBorderStyle	FixedDialog
    Text	Category Editor
    StartPosition	CenterScreen
    AcceptButton	btnOK
    CancelButton	btnCancel
    MaximizeBox	False
    MinimizeBox	False
    ShowInTaskbar	False

16. On the main menu, click Project -> Add Windows Form...
17. Set the Name to PartEditor and click Add
18. Design the form as follows:
     

    Control Text Name Other Properties Label &Year:     ComboBox   cbxYears   Label &Make:     ComboBox   cbxMakes   Button New C&ategory... btnNewMake   Label M&odel:     ComboBox   cbxModels   Button New Mo &del... btnNewModel   Label &Category:     ComboBox   cbxCategories   Button New Ca&tegory btnNewCategory   Label &Part Name:     TextBox   txtPartName   Label &Unit Price:     TextBox 0.00 txtUnitPrice TextAlign: Right Label Part #:     TextBox   txtPartNumber Enabled: False Button Submit btnSubmit   Button Close btnClose DialogResult: Cancel
    Form Property	Value
    FormBorderStyle	FixedDialog
    Text	College Park Auto -Parts: Part Editor
    StartPosition	CenterScreen
    MaximizeBox	False
    MinimizeBox	False
    ShowInTaskbar	False

19. Double-click the New Make button and implement its event as follows:
    

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.Data.SqlClient;
    
    namespace CollegeParkAutoParts3
    {
        public partial class PartEditor : Form
        {
            public PartEditor()
            {
                InitializeComponent();
            }
    
            private void btnNewMake_Click(object sender, EventArgs e)
            {
                MakeEditor editor = new MakeEditor();
    
                if (editor.ShowDialog() == DialogResult.OK)
                {
                    if (editor.txtMake.Text.Length > 0)
                    {
                        string strMake = editor.txtMake.Text;
    
                        // Make sure the category is not yet in the list
                        if (cbxMakes.Items.Contains(strMake))
                            MessageBox.Show(strMake + " is already in the list");
                        else
                        {
                            // Since this is a new category, add it to the combox box
                            cbxMakes.Items.Add(strMake);
                        }
    
                        cbxMakes.Text = strMake;
                    }
                }
            }        
        }
    }

20. Return to the Part Editor form and double-click the New Model button
21. Implement its event as follows:
    

    private void btnNewModel_Click(object sender, EventArgs e)
    {
        ModelEditor editor = new ModelEditor();
    
        if (editor.ShowDialog() == DialogResult.OK)
        {
            if (editor.txtModel.Text.Length > 0)
            {
                string strModel = editor.txtModel.Text;
    
                // Make sure the category is not yet in the list
                if (cbxModels.Items.Contains(strModel))
                    MessageBox.Show(strModel + " is already in the list");
                else
                {
                    // Since this is a new category, add it to the combox box
                    cbxModels.Items.Add(strModel);
                }
    
                cbxModels.Text = strModel;
            }
        }
    }

22. Return to the Part Editor form and double-click the New Category button
23. Implement its event as follows:
    

    private void btnNewCategory_Click(object sender, EventArgs e)
    {
        CategoryEditor editor = new CategoryEditor();
    
        if (editor.ShowDialog() == DialogResult.OK)
        {
            if (editor.txtCategory.Text.Length > 0)
            {
                string strCategory = editor.txtCategory.Text;
    
                // Make sure the category is not yet in the list
                if (cbxCategories.Items.Contains(strCategory))
                    MessageBox.Show(strCategory + " is already in the list");
                else
                {
                    // Since this is a new category, add it to the combo box
                    cbxCategories.Items.Add(strCategory);
                }
    
                cbxCategories.Text = strCategory;
            }
        }
    }

24. Return to the Part Editor form and double-click the Submit button
25. Implement the event as follows:
    

    private void btnSubmit_Click(object sender, EventArgs e)
    {
        double UnitPrice = 0.00;
    
        if (cbxYears.Text == "")
        {
            MessageBox.Show("You must specify the year of the car.");
            return;
        }
    
        if (cbxMakes.Text == "")
        {
            MessageBox.Show("You must specify the car manufacturer.");
            return;
        }
    
        if (cbxModels.Text == "")
        {
            MessageBox.Show("You must specify the car model.");
            return;
        }
    
        if (txtPartName.Text == "")
        {
            MessageBox.Show("You must enter the name of the part.");
            return;
        }
    
        if (txtUnitPrice.Text == "")
        {
            MessageBox.Show("You must enter the unit price of the part.");
            return;
        }
    
        try
        {
            UnitPrice = double.Parse(txtUnitPrice.Text);
        }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Unit Price.");
        }
    
        using (SqlConnection cnnNewPart =
               new SqlConnection("Data Source=(local);" +
                                 "Database=CollegeParkAutoParts1;" +
                                 "Integrated Security=SSPI;"))
        {
            string strAutoPart = "INSERT INTO AutoParts(" +
                                 "CarYear, Make, Model, Category, " +
                                 "PartName, UnitPrice) VALUES('" +
                                 cbxYears.Text + "', '" +
                                 cbxMakes.Text + "', '" +
                                 cbxModels.Text + "', '" +
                                 cbxCategories.Text + "', '" +
                                 txtPartName.Text + "', '" +
                                 txtUnitPrice.Text + "');";
    
            SqlCommand cmdAutoPart = new SqlCommand(strAutoPart, cnnNewPart);
    
            cnnNewPart.Open();
            cmdAutoPart.ExecuteNonQuery();
    
            MessageBox.Show("The new part has been added.");
        }
    }

26. Save the file and close the form
27. In the Solution Explorer, double-click CollegeParkAutoParts.cs to open the form
28. To create an icon, on the main menu, click Project -> Add New Item...
29. In the Templates list, click Icon File
30. Set the Name to cpap1 and click Add
31. Right-click the white area and click Delete Image Type
32. Design the 16x16, 16 colors version of the icon as follows:
     
    
33. On the main menu, click File -> Save cpap1.ico As
34. Select the bin\Debug folder of the current folder and click Save
35. On the main menu, click File -> Close
36. In the Solution Explorer, expand bin and expand Debug
37. In the Solution Explorer, right-click the Debug folder -> Add -> New Item...
38. In the Templates list, make sure Icon File is selected.
    Set the Name to cpap2 and click Add
39. Right-click the white area and click Delete Image Type
40. Design the 16x16, 16 colors version of the icon as follows:
     
    
41. Save the file and close the icon window
42. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
43. In the Templates list, make sure Icon File is selected.
    Set the Name to year1 and click Add
44. Right-click the white area and click Delete Image Type
45. Design the 16x16, 16 colors version of the icon as follows:
     
    
46. Save the file and close the icon window
47. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
48. In the Templates list, make sure Icon File is selected.
    Set the Name to year2 and click Add
49. Right-click the white area and click Delete Image Type
50. Design the 16x16, 16 colors version of the icon as follows:
     
    
51. Save the file and close the icon window
52. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
53. In the Templates list, make sure Icon File is selected.
    Set the Name to make1 and click Add
54. Right-click the white area and click Delete Image Type
55. Design the 16x16, 16 colors version of the icon as follows:
     
    
56. Save the file and close the icon window
57. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
58. In the Templates list, make sure Icon File is selected.
    Set the Name to make2 and click Add
59. Right-click the white area and click Delete Image Type
60. Design the 16x16, 16 colors version of the icon as follows:
     
    
61. Save the file and close the icon window
62. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
63. In the Templates list, make sure Icon File is selected.
    Set the Name to model1 and click Add
64. Right-click the white area and click Delete Image Type
65. Design the 16x16, 16 colors version of the icon as follows:
     
    
66. Save the file and close the icon window
67. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
68. In the Templates list, make sure Icon File is selected.
    Set the Name to model2 and click Add
69. Right-click the white area and click Delete Image Type
70. Design the 16x16, 16 colors version of the icon as follows:
     
    
71. Save the file and close the icon window
72. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
73. In the Templates list, make sure Icon File is selected.
    Set the Name to category1 and click Add
74. Right-click the white area and click Delete Image Type
75. Design the 16x16, 16 colors version of the icon as follows:
     
    
76. Save the file and close the icon window
77. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
78. In the Templates list, make sure Icon File is selected.
    Set the Name to category2 and click Add
79. Right-click the white area and click Delete Image Type
80. Design the 16x16, 16 colors version of the icon as follows:
     
    
81. Save the file and close the icon window
82. From the Components section of the Toolbox, click ImageList and click the form
83. In the Properties window, click (Name) and type imgAutoParts
84. Click the ellipsis button of the Images field
85. In the Image Collection Editor, click Add
86. Locate the folder that contains the icons you created and display it in the Look In combo box
87. Select cpap1.ico and click Open
88. In the same way, add the other pictures in the following order: cpap2.ico, year1.ico, year2.ico, make1.ico, make2.ico, model1.ico, model2.ico, category1.ico, and category1.ico
     
    
89. Click OK
90. Design the form as follows:
     

    Control Text Name Other Properties Label College Park Auto-Parts   Font: Times New Roman, 20.25pt, style=Bold ForeColor: Blue Panel     Height: 2 GroupBox Part Identification     TreeView   tvwAutoParts ImageList: imgAutoParts GroupBox Available Parts     ListView   lvwAutoParts FullRowSelect: True GridLines: True View: Details Columns   (Name) Text TextAlign Width colPartNumber Part #     colPartName Part Name   300 colUnitPrice Unit Price Right 80 GroupBox Customer Order - Selected Parts     Label Part #     Label Part Name     Label Unit Price     Label Qty     Label Sub Total     TextBox   txtPartNumber   TextBox   txtPartName   TextBox 0.00 txtUnitPrice TextAlign: Right TextBox 0 txtQuantity TextAlign: Right TextBox 0.00 txtSubTotal TextAlign: Right Button Add/Select btnAdd ListView   lvwSelectedParts FullRowSelect: True GridLines: True View: Details Columns   (Name) Text TextAlign Width colPartNumberSelected Part #   45 colPartNameSelected Part Name   274 colUnitPriceSelected Unit Price Right 58 colQuantitySelected Qty Right 28 colSubTotalSelected Sub-Total Right 58 GroupBox Order Summary Button New Au&to Part... btnNewAutoPart   Label Receipt #:   TextBox txtSave Button Save btnSave Label Tax Rate: TextBox 7.75 txtTaxRate TextAlign: Right Label % Label Parts Total: TextBox 0.00 txtPartsTotal TextAlign: Right Button &New Customer Order btnNewCustomerOrder   Label Receipt #:   TextBox txtOpen Button Save btnOpen Label Tax Amount: TextBox 0.00 txtTaxAmount TextAlign: Right Label Order Total: TextBox 0.00 txtOrderTotal TextAlign: Right Button Close btnClose

91. Click the Available Parts list view
92. In the Properties window, click the Events button and, in the Events section, double-click DoubleClick
93. Implement the event as follows:
    

    private void CollegeParkAutoParts_Load(object sender, EventArgs e)
    {
        // CreateDatabase();
    }
    
    private void lvwAutoParts_DoubleClick(object sender, EventArgs e)
    {
        ListViewItem lviAutoPart = lvwAutoParts.SelectedItems[0];
    
        if( (lvwAutoParts.SelectedItems.Count == 0) ||
            (lvwAutoParts.SelectedItems.Count > 1) )
                    return;
    
        txtPartNumber.Text = lviAutoPart.Text;
        txtPartName.Text = lviAutoPart.SubItems[1].Text;
        txtUnitPrice.Text = lviAutoPart.SubItems[2].Text;
    
        txtQuantity.Text = "1";
        txtSubTotal.Text = lviAutoPart.SubItems[2].Text;
    
        txtQuantity.Focus();
    }

94. Return to the CollegeParkAutoParts form
95. Click the Unit Price text box and, in the Events section of the Properties window, double-click Leave
96. Implement the event as follows:
    

    private void txtUnitPrice_Leave(object sender, EventArgs e)
    {
        double UnitPrice = 0.00D;
        int Quantity = 0;
        double SubTotal = 0.00D;
    
        try
        {
            UnitPrice = double.Parse(txtUnitPrice.Text);
        }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Unit Price!");
        }
    
        try { Quantity = int.Parse(txtQuantity.Text); }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Quandtity!");
        }
    
        SubTotal = UnitPrice * Quantity;
        txtSubTotal.Text = SubTotal.ToString("F");
    }
    
    internal void CalculateOrder()
    {
        if (lvwSelectedParts.Items.Count == 0)
        {
            txtTaxAmount.Text = "0.00";
            txtPartsTotal.Text = "0.00";
            txtOrderTotal.Text = "0.00";
            return;
        }
    
        // Calculate the current total order and update the order
        double PartsTotal = 0.00;
        double TaxRate = 0.00;
        double TaxAmount = 0.00;
        double OrderTotal = 0.00;
    
        foreach (ListViewItem lvi in lvwSelectedParts.Items)
        {
            ListViewItem.ListViewSubItem SubItem = lvi.SubItems[4];
    
            PartsTotal += double.Parse(SubItem.Text);
        }
    
        try
        {
            TaxRate = double.Parse(txtTaxRate.Text) / 100;
        }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Tax Rate");
        }
    
        TaxAmount = PartsTotal * TaxRate;
        OrderTotal = PartsTotal + TaxAmount;
    
        txtPartsTotal.Text = PartsTotal.ToString("F");
        txtTaxAmount.Text = TaxAmount.ToString("F");
        txtOrderTotal.Text = OrderTotal.ToString("F");
    }

97. Return to the CollegeParkAutoParts form and click the Qty text box
98. In the Events section of the Properties, click Leave, then click the arrow of its combo box and select txtUnitPrice_Leave
99. Return to the CollegeParkAutoParts form and click the Selected Part list view (the list view in the bottom-right section of the form)
100. In the Events section of the Properties window, double-click DoubleClick
101. Implement the event as follows:
     

     private void lvwSelectedParts_DoubleClick(object sender, EventArgs e)
     {
         ListViewItem lviSelectedPart = lvwSelectedParts.SelectedItems[0];
     
         if ((lvwSelectedParts.SelectedItems.Count == 0) ||
             (lvwSelectedParts.SelectedItems.Count > 1))
             return;
     
         txtPartNumber.Text = lviSelectedPart.Text;
         txtPartName.Text = lviSelectedPart.SubItems[1].Text;
         txtUnitPrice.Text = lviSelectedPart.SubItems[2].Text;
         txtQuantity.Text = lviSelectedPart.SubItems[3].Text;
         txtSubTotal.Text = lviSelectedPart.SubItems[4].Text;
     
         lvwSelectedParts.Items.Remove(lviSelectedPart);
         CalculateOrder();
     }

As reviewed above, before using a regular class to manipulate a database, you should first create a class. To do this, you must know the structure of the table that will be represented by the class. This means that you should be familiar with the tables in the data set object. After creating the class, to get the values from a table, you can declare a variable from a collection-based class. Then, you can use the properties and methods of the collection class, just as we saw in previous lessons.

1. In the Solution Explorer, right-click CollegeParkAutoParts3 -> Add -> Class...
2. Set the name to AutoPart and press Enter
3. Create a class as follows:
   

   using System;
   using System.Collections.Generic;
   using System.Linq;
   using System.Text;
   
   namespace CollegeParkAutoParts3
   {
       public class AutoPart
       {
           public int PartNumber;
           public int CarYear;
           public string Make;
           public string Model;
           public string Category;
           public string PartName;
           public double UnitPrice;
       }
   }

4. Display the Part Editor form and double-click an empty area of its body
5. Implement the event as follows:
   

   private void ResetPartEditor()
   {
       cbxYears.Items.Clear();
       cbxMakes.Items.Clear();
       cbxModels.Items.Clear();
       cbxCategories.Items.Clear();
       txtPartName.Text = "";
       txtUnitPrice.Text = "0.00";
       txtPartNumber.Text = "";
   
       // Put the years in the top combo box
       // Start with next year down to 1960
       for (int i = DateTime.Today.Year + 1; i >= 1960; i--)
           cbxYears.Items.Add(i.ToString());
   
       // Prepare a data set object for the parts
       DataSet dsParts = new DataSet("PartsSet");
   
       // Establish a connection to the database
       using (SqlConnection cnnParts =
           new SqlConnection("Data Source=(local);" +
                             "Database=CollegeParkAutoParts1;" +
                             "Integrated Security=SSPI;"))
       {
           // Create a command that will select the parts
           SqlCommand cmdParts =
               new SqlCommand("SELECT * FROM AutoParts;", cnnParts);
           // Open the connection
           cnnParts.Open();
   
           // Create a data adapter that will get the values from the table
           SqlDataAdapter sdaParts = new SqlDataAdapter(cmdParts);
           // Store those values in the data set
           sdaParts.Fill(dsParts);
   
           // Create an auto part object
           AutoPart StoreItem = null;
           // Create an empty list of auto parts
           List<AutoPart> lstAutoParts = new List<AutoPart>();
   
           // Check each record from the (only) table in the data set
           foreach (DataRow row in dsParts.Tables[0].Rows)
           {
               // Use the auto part object ...
               StoreItem = new AutoPart();
               // ... to create a record object
               StoreItem.PartNumber = int.Parse(row[0].ToString());
               StoreItem.CarYear = int.Parse(row[1].ToString());
               StoreItem.Make = row[2].ToString();
               StoreItem.Model = row[3].ToString();
               StoreItem.Category = row[4].ToString();
               StoreItem.PartName = row[5].ToString();
               StoreItem.UnitPrice = double.Parse(row[6].ToString());
               // Once the record is ready, store it in the collection variable
               lstAutoParts.Add(StoreItem);
           }
   
           // To avoid duplicate values in the combo boxes, 
           // we will use collection classes
           List<string> lstMakes = new List<string>();
           List<string> lstCategories = new List<string>();
   
           // Check the list of makes
           foreach (AutoPart part in lstAutoParts)
           {
               // If the list doesn't yet contain the make, add it
               if (!lstMakes.Contains(part.Make))
                   lstMakes.Add(part.Make);
           }
   
           // Once we have the list of makes, 
           // put them in the Make combo box
           foreach (string strMake in lstMakes)
               cbxMakes.Items.Add(strMake);
   
           foreach (AutoPart part in lstAutoParts)
           {
               if (!lstCategories.Contains(part.Category))
                   lstCategories.Add(part.Category);
           }
   
           foreach (string strCategory in lstCategories)
               cbxCategories.Items.Add(strCategory);
       }
   }
   
   private void PartEditor_Load(object sender, EventArgs e)
   {
       ResetPartEditor();
   }

6. Call the ResetPartEditor() method before the closing curly bracket of the Click event of the Submit button:
   

   private void btnSubmit_Click(object sender, EventArgs e)
   {
       . . . No Change            
                
       ResetPartEditor();
   }

7. Return to the Part Editor form and double-click the Year combo box
8. Implement the event as follows:
   

   private void cbxYears_SelectedIndexChanged(object sender, EventArgs e)
   {
       // If the user was working on a previous part, cancel it
       cbxModels.Items.Clear();
   }

9. Return to the Part Editor form and double-click the Make combo box
10. Implement its event as follows:
    

    private void cbxMakes_SelectedIndexChanged(object sender, EventArgs e)
    {
        // Create a data set of parts
        DataSet dsParts = new DataSet("PartsSet");
    
        // Establish a connection to the database
        using (SqlConnection cnnParts =
            new SqlConnection("Data Source=(local);" +
                              "Database=CollegeParkAutoParts1;" +
                              "Integrated Security=SSPI;"))
        {
    	// Create a command that will select the parts
            SqlCommand cmdParts = 
    	    new SqlCommand("SELECT * FROM AutoParts;", cnnParts);
    	// Open the connection
            cnnParts.Open();
    
    	// Create a data adapter that will get 
    	// the record from the command
            SqlDataAdapter sdaParts = new SqlDataAdapter(cmdParts);
    
    	// Store those records in the data set
            sdaParts.Fill(dsParts);
    
    	// Create an empty object that can receive one record
            AutoPart StoreItem = null;
    	// Create an empty list that can receive a list of records
            List<AutoPart> lstAutoParts = new List<AutoPart>();
    
    	// Check each record
            foreach (DataRow row in dsParts.Tables[0].Rows)
            {
    	    // Get the values of the current record
                StoreItem = new AutoPart();
    	    // Store the values in the object
                StoreItem.PartNumber = int.Parse(row[0].ToString());
                StoreItem.CarYear = int.Parse(row[1].ToString());
                StoreItem.Make = row[2].ToString();
                StoreItem.Model = row[3].ToString();
                StoreItem.Category = row[4].ToString();
                StoreItem.PartName = row[5].ToString();
                StoreItem.UnitPrice = double.Parse(row[6].ToString());
    	    // Once the record is ready, store it in the collection
                lstAutoParts.Add(StoreItem);
            }
    
    	// This will hold the list of parts
            List<string> lstModels = new List<string>();
    
            foreach (AutoPart part in lstAutoParts)
            {
                if ((part.CarYear == int.Parse(cbxYears.Text)) &&
                    (part.Make == cbxMakes.Text))
                {
                    if (!lstModels.Contains(part.Model))
                        lstModels.Add(part.Model);
                }
            }
    
            foreach (string strModel in lstModels)
                cbxModels.Items.Add(strModel);
        }
    }

11. Access the CollegeParkAutoParts form, right-click it and click View Code
12. Make the following changes:
    

    void ShowAutoParts()
    {
        tvwAutoParts.Nodes.Clear();
        TreeNode nodRoot = 
    	tvwAutoParts.Nodes.Add("College Park Auto-Parts",
                                   "College Park Auto-Parts", 0, 1);
        // Show the years nodes
        for (int years = DateTime.Today.Year + 1; years >= 1960; years--)
            nodRoot.Nodes.Add(years.ToString(), years.ToString(), 2, 3);
    
        tvwAutoParts.SelectedNode = nodRoot;
        // Expand the root node
        tvwAutoParts.ExpandAll();
    
        // Create an empty data set
        DataSet dsParts = new DataSet("PartsSet");
    
        // Create a connection to the database
        using (SqlConnection cnnParts =
            new SqlConnection("Data Source=(local);" +
                              "Database=CollegeParkAutoParts1;" +
                              "Integrated Security=SSPI;"))
        {
            // Use a command to specify what action we want to take
            SqlCommand cmdParts = 
    		new SqlCommand("SELECT * FROM AutoParts;", cnnParts);
            // Open the connection
            cnnParts.Open();
    
            // Use a data adapter to retrieve the values from the command
            SqlDataAdapter sdaParts = new SqlDataAdapter(cmdParts);
            // Fill the data set with the values from the data adapater
            sdaParts.Fill(dsParts);
    
            // Prepare a variable from the class we will use
            AutoPart StoreItem = null;
            // Create a collection
            List<AutoPart> lstAutoParts = new List<AutoPart>();
    
            // Check each record from the table from the data set
            foreach (DataRow row in dsParts.Tables[0].Rows)
            {
                // Identify each record as a value of our class
                StoreItem = new AutoPart();
                // Get the values of the record and put them in the class
                StoreItem.PartNumber = int.Parse(row[0].ToString());
                StoreItem.CarYear = int.Parse(row[1].ToString());
                StoreItem.Make = row[2].ToString();
                StoreItem.Model = row[3].ToString();
                StoreItem.Category = row[4].ToString();
                StoreItem.PartName = row[5].ToString();
                StoreItem.UnitPrice = double.Parse(row[6].ToString());
                // Store the record in the collection
                lstAutoParts.Add(StoreItem);
            }
    
            // Now that we have the records, 
            // we can use them as a normal collection
            foreach (TreeNode nodYear in nodRoot.Nodes)
            {
                List<string> lstMakes = new List<string>();
    
                foreach (AutoPart  part in lstAutoParts)
                {
                    if (nodYear.Text == part.CarYear.ToString())
                    {
                        if (!lstMakes.Contains(part.Make))
                            lstMakes.Add(part.Make);
                    }
                }
    
                foreach (string strMake in lstMakes)
                    nodYear.Nodes.Add(strMake, strMake, 4, 5);
            }
    
            foreach (TreeNode nodYear in nodRoot.Nodes)
            {
                foreach (TreeNode nodMake in nodYear.Nodes)
                {
                    List<string> lstModels = new List<string>();
    
                    foreach (AutoPart  part in lstAutoParts)
                    {
                        if ((nodYear.Text == part.CarYear.ToString()) &&
                            (nodMake.Text == part.Make))
                        {
                            if (!lstModels.Contains(part.Model))
                                lstModels.Add(part.Model);
                        }
                    }
    
                    foreach (string strModel in lstModels)
                        nodMake.Nodes.Add(strModel, strModel, 6, 7);
                }
            }
    
            foreach (TreeNode nodYear in nodRoot.Nodes)
            {
                foreach (TreeNode nodMake in nodYear.Nodes)
                {
                    foreach (TreeNode nodModel in nodMake.Nodes)
                    {
                        List<string> lstCategories = new List<string>();
    
                        foreach (AutoPart  part in lstAutoParts)
                        {
                            if ((nodYear.Text == part.CarYear.ToString()) &&
                                (nodMake.Text == part.Make) &&
                                (nodModel.Text == part.Model))
                            {
                                if (!lstCategories.Contains(part.Category))
                                    lstCategories.Add(part.Category);
                            }
                        }
    
                        foreach (string strCategory in lstCategories)
                        nodModel.Nodes.Add(strCategory, strCategory, 8, 9);
                    }
                }
            }
        }
    }
    
    private void CollegeParkAutoParts_Load(object sender, EventArgs e)
    {
        // CreateDatabase();
        ShowAutoParts();
    }
    
    . . . No Change
    	
    

13. Return to the CollegeParkAutoParts form and double-click the New Auto Part button
14. Implement the event as follows:
    

    private void btnNewAutoPart_Click(object sender, EventArgs e)
    {
        PartEditor editor = new PartEditor();
    
        if (editor.ShowDialog() == DialogResult.Cancel)
            ShowAutoParts();
    }

15. Execute the application
16. Click the New Auto Part button and use the Part Editor to create a few parts
17. Close the forms and return to your programming environment
18. Access the  CollegeParkAutoParts form and click the tree view
19. In the Properties window, click the Events button and, in the Events section, double-click NodeMouseClick
20. Implement the event as follows:
    

    private void tvwAutoParts_NodeMouseClick(object sender, 
    		TreeNodeMouseClickEventArgs e)
    {
        TreeNode nodClicked = e.Node;
    
        if (nodClicked.Level == 4)
            lvwAutoParts.Items.Clear();
    
        DataSet dsParts = new DataSet("PartsSet");
    
        using (SqlConnection cnnParts =
            new SqlConnection("Data Source=(local);" +
                              "Database=CollegeParkAutoParts1;" +
                              "Integrated Security=SSPI;"))
        {
            SqlCommand cmdParts = 
    		new SqlCommand("SELECT * FROM AutoParts;", cnnParts);
            cnnParts.Open();
    
            SqlDataAdapter sdaParts = new SqlDataAdapter(cmdParts);
            sdaParts.Fill(dsParts);
    
            AutoPart StoreItem = null;
            List<AutoPart> lstAutoParts = new List<AutoPart>();
    
            foreach (DataRow row in dsParts.Tables[0].Rows)
            {
                StoreItem = new AutoPart();
                StoreItem.PartNumber = int.Parse(row[0].ToString());
                StoreItem.CarYear = int.Parse(row[1].ToString());
                StoreItem.Make = row[2].ToString();
                StoreItem.Model = row[3].ToString();
                StoreItem.Category = row[4].ToString();
                StoreItem.PartName = row[5].ToString();
                StoreItem.UnitPrice = double.Parse(row[6].ToString());
               lstAutoParts.Add(StoreItem);
           }
    
           try
           {
                foreach (AutoPart part in lstAutoParts)
                {
                    if ((part.Category == nodClicked.Text) &&
                        (part.Model == nodClicked.Parent.Text) &&
                        (part.Make == nodClicked.Parent.Parent.Text) &&
                        (part.CarYear.ToString() == 
    			nodClicked.Parent.Parent.Parent.Text))
                    {
                        ListViewItem lviAutoPart =
                            new ListViewItem(part.PartNumber.ToString());
    
                        lviAutoPart.SubItems.Add(part.PartName);
                  lviAutoPart.SubItems.Add(part.UnitPrice.ToString("F"));
                        lvwAutoParts.Items.Add(lviAutoPart);
                    }
                }
            }
            catch (NullReferenceException)
            {
            }
        }
    }

21. Return to the CollegeParkAutoParts form and double-click the Add/Select button
22. Implement the event as follows:
    

    private void btnAdd_Click(object sender, EventArgs e)
    {
        if (txtPartNumber.Text.Length == 0)
        {
            MessageBox.Show("There is no part to be added to the order");
            return;
        }
                
        DataSet dsParts = new DataSet("PartsSet");
    
        using (SqlConnection cnnParts =
              new SqlConnection("Data Source=(local);" +
                                "Database=CollegeParkAutoParts1;" +
                                "Integrated Security=SSPI;"))
        {
            SqlCommand cmdParts = 
    	    new SqlCommand("SELECT * FROM AutoParts;", cnnParts);
            cnnParts.Open();
    
            SqlDataAdapter sdaParts = new SqlDataAdapter(cmdParts);
            sdaParts.Fill(dsParts);
    
            AutoPart StoreItem = null;
            List<AutoPart> lstAutoParts = new List<AutoPart>();
    
            foreach (DataRow row in dsParts.Tables[0].Rows)
            {
                StoreItem = new AutoPart();
                StoreItem.PartNumber = int.Parse(row[0].ToString());
                StoreItem.CarYear = int.Parse(row[1].ToString());
                StoreItem.Make = row[2].ToString();
                StoreItem.Model = row[3].ToString();
                StoreItem.Category = row[4].ToString();
                StoreItem.PartName = row[5].ToString();
                StoreItem.UnitPrice = double.Parse(row[6].ToString());
                lstAutoParts.Add(StoreItem);
            }
    
            foreach (AutoPart part in lstAutoParts)
            {
                 if (part.PartNumber == int.Parse(txtPartNumber.Text))
                 {
                    ListViewItem lviSelectedPart =
                        new ListViewItem(part.PartNumber.ToString());
    
                    lviSelectedPart.SubItems.Add(part.PartName);
                    lviSelectedPart.SubItems.Add(part.UnitPrice.ToString());
                    lviSelectedPart.SubItems.Add(txtQuantity.Text);
                    lviSelectedPart.SubItems.Add(txtSubTotal.Text);
                    lvwSelectedParts.Items.Add(lviSelectedPart);
                }
            }
    
            CalculateOrder();
        }
    }

23. Return to the CollegeParkAutoParts form and double-click the Save Customer Order button
24. Implement the event as follows:
    

    private void btnSaveCustomerOrder_Click(object sender, EventArgs e)
    {
        if (lvwSelectedParts.Items.Count == 0)
            return;
        else
        {
            int ReceiptNumber = 0;
            string strReceiptNumber = "";
    
            // The following code allows us to get 
    	// the highest receipt number
            //1. Create a connection to the database
            using (SqlConnection cnnReceiptNumber =
                   new SqlConnection("Data Source=(local);" +
                                     "Database=CollegeParkAutoParts1;" +
                                     "Integrated Security=SSPI;"))
            {
                // Use the MAX() function to locate 
    	    // the highest receipt number
                string strSelect = 
    		"SELECT MAX(ReceiptNumber) FROM CustomersOrders;";
                SqlCommand cmdReceiptNumber = 
    		new SqlCommand(strSelect, cnnReceiptNumber);
    
                // 2. Open the connection
                cnnReceiptNumber.Open();
    
                // 3. Use a data reader to get 
    	    //  the values from the Customer Orders table
                SqlDataReader rdrReceiptNumber = 
    		cmdReceiptNumber.ExecuteReader();
    
                // 4. Read through the receipt numbers to get to the last
                while (rdrReceiptNumber.Read())
                    strReceiptNumber = rdrReceiptNumber[0].ToString();
    
                // If there is no receipt number (yet), 
    	    // then set the first to 1000
                if (strReceiptNumber == "")
                    strReceiptNumber = "1000";
    
                // Now that we have a receipt number, we will increase it by 1
                ReceiptNumber = int.Parse(strReceiptNumber) + 1;
            }
    
            // The following variable will hold the whole INSERT statement
            string strCustomerOrder = "";
    
            // Check each selected part and get it ready to add to the table
            // Each selected part of this order will have a common receipt #
            for (int i = 0; i < lvwSelectedParts.Items.Count; i++)
            {
                strCustomerOrder = 
    		strCustomerOrder + 
    		"INSERT INTO CustomersOrders(" +
                    "ReceiptNumber, PartNumber, PartName, " +
                    "UnitPrice, Quantity, SubTotal) VALUES('" +
                    ReceiptNumber.ToString() + "', '" +
                    lvwSelectedParts.Items[i].Text + "', '" +
                    lvwSelectedParts.Items[i].SubItems[1].Text + "', '" +
                    lvwSelectedParts.Items[i].SubItems[2].Text + "', '" +
                    lvwSelectedParts.Items[i].SubItems[3].Text + "', '" +
                    lvwSelectedParts.Items[i].SubItems[4].Text + "'); ";
            }
    
            // We will also use the same common receipt number 
            // to save the values of the receipt
             strCustomerOrder = 
    		strCustomerOrder + 
    		"INSERT INTO CustomersOrders(" +
                    "ReceiptNumber, PartsTotal, TaxRate, " +
                    "TaxAmount, OrderTotal) VALUES('" +
                    ReceiptNumber.ToString() + "', '" +
                    txtPartsTotal.Text + "', '" +
                    txtTaxRate.Text + "', '" +
                    txtTaxAmount.Text + "', '" +
                    txtOrderTotal.Text + "');";
    
            using (SqlConnection cnnCustomerOrder =
                   new SqlConnection("Data Source=(local);" +
                                     "Database=CollegeParkAutoParts1;" +
                                     "Integrated Security=SSPI;"))
            {
                SqlCommand cmdCustomerOrder = 
    		new SqlCommand(strCustomerOrder, cnnCustomerOrder);
                cnnCustomerOrder.Open();
    
                cmdCustomerOrder.ExecuteNonQuery();
    
                // Let the user know that the order has been created
                MessageBox.Show("The customer order has been saved.");
                // Reset the form
                btnNewCustomerOrder_Click(sender, e);
            }
        }
    }

25. Return to the CollegeParkAutoParts form and double-click the Open button
26. Implement the event as follows:
    

    private void btnOpen_Click(object sender, EventArgs e)
    {
        lvwSelectedParts.Items.Clear();
    
        using (SqlConnection cnnCustomerOrder =
               new SqlConnection("Data Source=(local);" +
                                 "Database=CollegeParkAutoParts1;" +
                                 "Integrated Security=SSPI;"))
        {
            string strSelect = "SELECT * FROM CustomersOrders " +
                               "WHERE (ReceiptNumber = '" +
                               txtReceiptNumber.Text + "') AND " +
                               "PartNumber IS NOT NULL;";
    
            SqlCommand cmdCustomerOrder =
            new SqlCommand(strSelect, cnnCustomerOrder);
            SqlDataAdapter sdaCustomerOrder =
    	        new SqlDataAdapter(cmdCustomerOrder);
    
            cnnCustomerOrder.Open();
    
            DataSet dsCustomerOrder = new DataSet("CustomersOrdersSet");
            sdaCustomerOrder.Fill(dsCustomerOrder);
    
            for (int i = 0; i < dsCustomerOrder.Tables[0].Rows.Count; i++)
            {
                DataRow rowOrder = dsCustomerOrder.Tables[0].Rows[i];
    
                ListViewItem lviOrder =
                    new ListViewItem(rowOrder["PartNumber"].ToString());
                lviOrder.SubItems.Add(rowOrder["PartName"].ToString());
                lviOrder.SubItems.Add(rowOrder["UnitPrice"].ToString());
                lviOrder.SubItems.Add(rowOrder["Quantity"].ToString());
                lviOrder.SubItems.Add(rowOrder["SubTotal"].ToString());
                lvwSelectedParts.Items.Add(lviOrder);
            }
        }
    
        using (SqlConnection cnnInvoice =
               new SqlConnection("Data Source=(local);" +
                                 "Database=CollegeParkAutoParts1;" +
                                 "Integrated Security=SSPI;"))
        {
            string strInvoice = "SELECT ReceiptNumber, PartsTotal, TaxRate, " +
                                "TaxAmount, OrderTotal " +
                                "FROM CustomersOrders " +
                                "WHERE (ReceiptNumber = '" +
                                txtReceiptNumber.Text + "') AND " +
                                "      (PartNumber IS NULL) AND " +
                                "      (PartName IS NULL);";
    
            SqlCommand cmdInvoice = new SqlCommand(strInvoice, cnnInvoice);
    
            cnnInvoice.Open();
            SqlDataReader rdrInvoice = cmdInvoice.ExecuteReader();
    
            while (rdrInvoice.Read())
            {
                txtPartsTotal.Text = rdrInvoice[1].ToString();
                txtTaxRate.Text = rdrInvoice[2].ToString();
                txtTaxAmount.Text = rdrInvoice[3].ToString();
                txtOrderTotal.Text = rdrInvoice[4].ToString();
            }
        }
    }

27. Return to the CollegeParkAutoParts form and double-click the New Customer button
28. Implement the event as follows:
    

    private void btnNewCustomerOrder_Click(object sender, EventArgs e)
    {
        ShowAutoParts();
        lvwAutoParts.Items.Clear();
        txtPartNumber.Text = "";
        txtPartName.Text = "";
        txtUnitPrice.Text = "0.00";
        txtQuantity.Text = "0";
        txtSubTotal.Text = "0.00";
        lvwSelectedParts.Items.Clear();
        txtPartsTotal.Text = "0.00";
        txtTaxRate.Text = "5.75";
        txtTaxAmount.Text = "0.00";
        txtOrderTotal.Text = "0.00";
        txtReceiptNumber.Text = "";
    }

29. Return to the CollegeParkAutoParts form and double-click the Close button
30. Implement the event as follows:
    

    private void btnClose_Click(object sender, EventArgs e)
    {
        Close();
    }

31. Create a few customer orders and save them
32. Close the forms and return to your programming environment
33. Execute the application again and open a previously saved order
34. Close the forms and return to your programming environment