1 Low Level ADO.NET Operations II Microsoft Visual C# 2008 Step by Step Chapter 25

2 Getting Started Download and expand the Northwind Product Browser as we left it last class. Downloads/2011_03_31_Low_Level_ADO_Operations/ Downloads/2011_03_31_Low_Level_ADO_Operations/ File Northwind_Product_Browser.zip Build and run

3 SqlDataReader Class SqlDataReader provides two ways for us to access various columns of the current query result: Column name Position

4 Access by Column Name We have seen one example of the name based method Form1.cs, btnGetData_Click while (rdr.Read()) { String Product_Name = (String)rdr["ProductName"]; Product_List.Add(Product_Name); }

5 Access by Position We could have written: while (rdr.Read()) { String Product_Name = rdr.GetString(0); Product_List.Add(Product_Name); } Get column 0 of the current query result, as a String. No typecast necessary.

6 Reading Other Datatypes The SqlDataReader class has a postion based method for each datatype. GetString() GetInt32() GetInt16() GetDecimal() GetBoolean() … You have to use the right one for the data type of column you want to retrieve. But then you don’t have to typecast the result.

7 Product Browser Let’s extend the Product Browser to display more information about each product.

8 Table Products Contents

9 Table Products Definition

10 Product_Information Form Extended

11 Add Class Product using System; namespace Product_Browser { class Product { private String product_name; private int product_id; private decimal unit_price; private int units_in_stock; private bool discontinued ; }

12 Define Properties for Product Fields Select field. Refactor > Encapsulate Field

13 Product_List In Form1.cs modify Product_List to be a list of Products. List Product_List = new List ();

14 Changes to Form1.cs New SQL command in Form1.cs, Get_SqlDataReader : SqlCommand1.CommandText = "SELECT * FROM Products ORDER BY ProductName";

15 Recall Definition of Table Products

16 Update btnGetData_Click while (rdr.Read()) { Product p = new Product(); p.Product_name = rdr.GetString(1); p.Product_id = rdr.GetInt32(0); if (rdr.IsDBNull(5)) { p.Unit_price = 0.00M; } else { p.Unit_price = rdr.GetDecimal(5); } Must check any column that could be Null. A Decimal literal (M for “money”)

17 More Compactly while (rdr.Read()) { Product p = new Product(); p.Product_name = rdr.GetString(1); p.Product_id = rdr.GetInt32(0); p.Unit_price = rdr.IsDBNull(5) ? 0.0M : rdr.GetDecimal(5); p.Units_in_stock = rdr.IsDBNull(6) ? 0 : rdr.GetInt16(6); p.Discontinued = rdr.GetBoolean(9); Product_List.Add(p); }

18 Changes to Product_Information.cs Update references to List to be List. Update Display_Current_Record as shown on next slide.

19 Chanages to Display_Current_Record() private void Display_Current_Record() { Product p = (Product) Product_List[Current_Record_Number]; tbProductName.Text = p.Product_name; tbProductID.Text = p.Product_id.ToString(); tbUnitPrice.Text = p.Unit_price.ToString("C"); tbUnitsInStock.Text = p.Units_in_stock.ToString(); cbDiscontinued.Checked = p.Discontinued; tbRecordNumber.Text = "Record " + (Current_Record_Number + 1) + " of " + Product_List.Count; Update_Buttons(); } Format as currency Build and run.

20 Compile Error!

21 Class Product We have to declare class Product as “public”.

22 Class Product Try again to build and run.

23 Enhanced Product Browser in Action End of Section

24 A Better Solution Forms should be limited to just UI functions. Knowledge of how products are represented in the database is better confined to a separate class. Separation of responsibilities. Let class Product be responsible for knowledge of how to initialize a product object using results of a database query. Anyone else who needs product info should use the Product class.

25 Class Product We will add a constructor that takes the query result as a parameter. Initializes object with data from a SqlDataReader. Add using System.Data.SqlClient;

26 Class Product Constructor // This constructor initializes a product using a query result. public Product(SqlDataReader rdr) { Product_name = rdr.GetString(1); Product_id = rdr.GetInt32(0); Unit_price = rdr.IsDBNull(5) ? 0.0M : rdr.GetDecimal(5); Units_in_stock = rdr.IsDBNull(6) ? 0 : rdr.GetInt16(6); Discontinued = rdr.GetBoolean(9); } Copy from btnGetData_Click()

27 Class Products Let another class be responsible for knowledge of how to do the query. Static class Products will hold a static method Get_Products. Code previously included in Form1 Make username and password parameters. Return List No constructor. The class cannot be instantiated. Just a home for the static Get_Products method.

28 Get_Products() public static List Get_Products(String Username, String Password) { List Product_List = new List (); SqlDataReader rdr; SqlConnection SqlConnection1; SqlConnection1 = Setup_Connection(Username, Password); rdr = Get_SqlDataReader(SqlConnection1); while (rdr.Read()) { Product p = new Product(rdr); Product_List.Add(p); } rdr.Close(); SqlConnection1.Close(); return Product_List; }

29 Setup_Connection() private static SqlConnection Setup_Connection(String Username, String Password) { String connection_string = "server=scorpius.eng.usf.edu; " + "database=Northwind;" + "User=" + Username + "; " + "Password=" + Password; SqlConnection SqlConnection1 = new SqlConnection(connection_string); SqlConnection1.Open(); return SqlConnection1; }

30 Get_SqlDataReader() private static SqlDataReader Get_SqlDataReader( SqlConnection SqlConnection1) { SqlCommand SqlCommand1 = new SqlCommand(); SqlCommand1.CommandText = "SELECT * FROM Products ORDER BY ProductName"; SqlCommand1.Connection = SqlConnection1; return SqlCommand1.ExecuteReader(); }

31 Form1.cs private void btnGetData_Click(object sender, EventArgs e) { try { Product_List = Products.Get_Products(tbUserName.Text, tbPassword.Text); } catch (Exception ex) { MessageBox.Show(ex.Message); return; } // Instantiate the form that displays product information. Product_Information pif = new Product_Information(Product_List); this.Hide(); pif.ShowDialog(); this.Close(); }

32 A Better Solution The functionality is unchanged from previous version. Class Form1 is now simpler. Limited to UI functions. Class Products is responsible for interfacing with the database. Class Product is responsible for internal representation of products. This is an example of refactoring.

33 Assignment Before next class: Explore the Northwind Traders database. Familiarize yourself with its tables. Browse with Visual Studio or Management Studio Express. Try some queries. If you haven't already done so, download and read the Northwind Traders Call Center concept document from the Downloads area of the class web site: Downloads/Northwind_Call_Center/ File Concept_v1_3.doc Downloads/Northwind_Call_Center/ End of Presentation