1. 9-1 Chapter 9 Working with Databases in VB.NET

2. 9-2 Learning Objectives Understand how databases are used to store business data and how they differ from arrays. Describe the parts of a database and understand database operations including working with ADO.NET and the Dataset. Add oleDBDataAdapter and DataGrid controls to a form and configure them to display records from a database table.

3. 9-3 Learning Objectives (continued) Add the necessary code to find and display records that match some criteria. Add programming instructions and controls to edit database records, add new records, delete existing records, and print records in the Dataset. Use VB.NET and an ADO.NET database to carry out the rental of a DVD.

4. 9-4 Database concepts Database – The storage of different types of data in a such a way that the data can be easily manipulated and retrieved by an end user. Field – A single fact or data item, the smallest unit of named data that has meaning in a database. – Examples A name, address, or phone number on a membership list; A product number in an inventory list; or a price in a price list. – Fields are given field names that are used to identify them.

5. 9-5 More Database Concepts Record – A collection of related data that is treated as a unit – For example, a membership list record that contains numerous fields, including name, phone number, street address, city, state, Zip code Table – A related collection of records, all having the same fields – A table for the Vintage DVDs membership list would have a record for each person on the list In a table, the records are commonly referred to as the rows of the table and the fields are the columns of the table.

6. 9-6 Relational Databases A database with multiple tables that are related is known as a relational database. The most common type of database used today – MS Access – MS SQL Server

7. 9-7 Relational Database Example

8. 9-8 Primary Key and Foreign Key Primary Key – A field in a table that uniquely identifies a record in that same table – In a table containing customers, the Social Security Number field could be the primary key – No two individuals have the same Social Security Number Foreign Key – A field in a table that uniquely identifies a record in another table – In a table containing Payments information, a single field would be used to keep track of who made the payment. – That field (say Social Security Number) is a foreign key

9. 9-9 Database Operations The primary use of a database – To enable the user to obtain information from it in a usable form by constructing queries – For a relational database, these queries are written in a special language known as SQL (for Structured Query Language), Queries enable database users to find records from a table that meet some stated criterion or to create composite records from multiple tables that meet the criterion.

10. 9-10 Databases vs Arrays A database table can store multiple types of data in the same table Any changes to the database are immediately saved to disk as they occur. We can use a sophisticated database engine to handle the processing. It is very easy to connect multiple computers to the same database, so that any changes are immediately known to all computers. Arrays are restricted to a single data type. Arrays are inherently volatile, you need to write code to “persist” changes Array operations all require customized code No such immediate update, still requires code

11. 9-11 Databases in VB.NET ADO.Net – Active Data Object.Net – The data access framework used in VB.Net We use Access as database Similar coding approach would work with any database providing an OLEDB interface

12. 9-12 Step-by-step 9-1: Starting database project Demo

13. 9-13 VB.Net Data Objects and Wizards Data Adapter object – Acts as intermediary between the database on disk and disconnected in-memory representations of the database called DataSets and DataTables DataSet – can be made up of one or more database tables along with their relations DataTable – One table from the database

14. 9-14 ADO.Net’s way: Disconnected Views In ADO.Net typical programming, DataSet’s and DataTable’s are disconnected They are created from the database in computer memory They are manipulated in memory The results are used to update the original database on disk when desired

15. 9-15 Data Adapters in VB.Net Two types of data adapters in VB.NET – oleDbDataAdapter Designed to work with a number of types of databases including Access databases The most generic adapter – sqlDbDataAdapter Specifically designed to work with Microsoft SQL Server databases The most specific adapter

16. 9-16 Data Objects in the Toolbox

17. 9-17 Configuring a Data Adapter 1. Set up database connection 2. Generate SQL to display fields from a table of the database 3. Generate a Dataset

18. 9-18 Setting up a database Connection

19. 9-19 Setting up a database connection

20. 9-20 Creating the SQL to display fields

21. 9-21 The Query Builder

22. 9-22 Generating a dataset Two ways to generate a dataset – Click the “Generate Dataset” hyperlink below the Property window when either the form or data adapter control is selected – Select the Data|Generate Dataset menu option What it does – Creates a class from which a DataSet object can be instantiated – Instantiates an object from the class

23. 9-23 Dataset Generation Dialog Box

24. 9-24 Step-by-Step 9-2: Connecting to the database Demo

25. 9-25 Displaying records in DataGrid Add a DataGrid control to project Set the DataSource property of the control – Use the properties window – At this point, the grid knows the name of the Fields but not the values of the records Fill the DataGrid by calling the Fill method of the DataAdapter to which it is “bound” – oleDBDataAdapter1.Fill(DataSetName,TableName)

26. 9-26 Searching for records Need an SQL Query – General form SELECT fieldnames FROM tables WHERE query ORDER BY fieldname; – Use the * character to indicate all fields SELECT * FROM MyTable – Not all parts of the general form are necessary

27. 9-27 More SQL SELECT * FROM Members WHERE Late_Fees > 10 – Selects only those members with more than $10 in late fees SELECT * FROM Members ORDER By Phone_Number – Order (ascending) the members by their phone number – To obtain a descending order, append DESC at the end SELECT * FROM Members WHERE Phone_Number = ‘706-555-1234’ – Failure to include the apostrophes will lead to an error – The apostrophes indicate a literal string value in SQL

28. 9-28 Implementing a Search Clear the Dataset Create the appropriate query string – Usually on the fly according to some user input Modify the data adapter to use the new query string rather than the one created with the Query Builder wizard during the data adapter configuration process.

29. 9-29 Code for the Search Sub procedure to search for late fees Sub FindLateFees(ByVal decAmount As Decimal) Dim SelString As String DsVintage1.Clear() SelString = "SELECT * “ & _ “FROM Members “ & _ “WHERE Late_Fees > Cstr(decAmount)” MembersAdapter.SelectCommand.CommandText = SelString MembersAdapter.Fill(DsVintage1, "Members") End Sub

30. 9-30 The LIKE operator The general form of the query using the LIKE Operator is: – SELECT * FROM – Table WHERE FieldName – LIKE ’%SearchString%’ % is the wild card character for strings % can be replaced by any number of other characters

31. 9-31 Step-by-Step 9-3: Displaying records in a DataGrid Demo

32. 9-32 Record Operations Editing a record in the DataGrid by changing one or more fields and saving the results back to the database Adding a new record to the database Deleting an existing record Reading records

33. 9-33 Editing records Editing a record that appears in the DataGrid and saving the changes back to the underlying database table is a two-step process: 1. Make changes directly into the cell in the DataGrid 2. Update these changes to modify the database

34. 9-34 Adding a new record 1. Use a dialog form like that discussed in Chapter 8 to input multiple items of data and transfer them to variables in the btnAdd_Click event procedure in the frmMembers code window 2. Create a new row of the Dataset table composed of the variable contents from Step 1 Make sure no row already exists with same primary key 3. Add the new row to the Dataset table and update the database.

35. 9-35 Adding a Row to DataSet Sub AddMembers(ByVal strName As String, ByVal strPhoneNumber As String) ‘Declare a DataRow variable Dim Member_Row As DataRow ‘Create a new DataRow and assign to the DataRow variable Member_Row = DsVintage1.Tables("Members").NewRow ‘Assign values to each of the fields Member_Row("Name") = strName Member_Row("Phone_Number") = strPhoneNumber Member_Row("Late_Fees") = 0 ‘Add the DataRow to the Rows collection of the table DsVintage1.Tables("Members").Rows.Add(Member_Row) ‘Update the database with the changes made to it MembersAdapter.Update(DsVintage1, "Members") End Sub

36. 9-36 Error Handling: The Try-Catch structure The complete form of the Try-Catch structure is: Try Programming statement to be tested Catch variable As exception error Programming statement to be executed if error is caught Finally Programming statements to be executed in all cases End Try

37. 9-37 Deleting a record Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _ Handles btnDelete.Click Const strDelete As String = "Are you sure you want to delete this record?" Dim strPhoneNumber As String, intNumRows, intResponse As Integer strPhoneNumber = InputBox("Input phone number of person to be deleted.") FindPhoneNumber(strPhoneNumber) intNumRows = DsVintage1.Tables("Members").Rows.Count If intNumRows = 0 Then MsgBox("Nobody with that telephone number!") Exit Sub End If intResponse = MsgBox(strDelete, vbYesNoCancel + vbCritical + vbDefaultButton2, "Delete Record") If intResponse = vbYes Then DsVintage1.Tables("Members").Rows(0).Delete() MembersAdapter.Update(DsVintage1, "members") Else MsgBox("Record not deleted", vbInformation, "Vintage") End If End Sub

38. 9-38 FindPhoneNumber Sub FindPhoneNumber(ByVal strPhNum As String) Dim strSelectString As String DsVintage1.Clear() strSelectString = “SELECT * “ & _ “FROM Members “ & “WHERE " & _ "Phone_Number = '" & strPhNum & "'“ MembersAdapter.SelectCommand.CommandText = _ strSelectString MembersAdapter.Fill(DsVintage1, "Members") End Sub

39. 9-39 Reading Matching Records Need two new objects – oleDBCommand – oleDBDataReader The oleDBCommand control can be dragged from the toolbox Use the oleDBCommand objet to generate the oleDBDataReader The oleDBDataReader is used to simply read through a Dataset without making any changes

40. 9-40 Code to read matching records Private Sub btnPrint_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnPrint.Click Dim datReader As OleDb.OleDbDataReader, strOutput As String MembersConnection.Open() ‘MembersCommand is an OleDBCommand object datReader = MembersCommand.ExecuteReader While datReader.Read() strOutput = datReader("Name").ToString() _ & vbTab & datReader("Phone_Number").ToString() _ & vbTab & _ Format(datReader("late_fees").ToString, "currency") Debug.WriteLine(strOutput) End While End Sub

41. 9-41 Step-by-Step 9-4: Record Operations Demo

42. 9-42 Step-by-Step 9-5: Renting a DVD Demo

43. 9-43 Copyright 2004 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein