1. Database vs. DBMS Database Database Management System
A collection of organized, related tables (data stored in rows and columns)
Database Management System
Also known as DBMS
Software used to create and maintain a database

2. Entity-Relationship Diagram
Also known as ERD
Graphical representation showing the relationships of entities in a database
Entities
things of interest to business (products, employees, suppliers, customers, purchases, sales,…)
Relationships
real-world associations between entities
products purchased by customers
employees who designed a particular part
suppliers who provided a particular raw material

3. ERD Cardinality Related to one Related to one or zero (optional)
Related to zero or more
Related to one or more
Student
Course
Teacher
Each course belongs to a specific teacher (manager)
A teacher may teach one or more courses
A student can sign up for one or more courses
A course may have no students (not offered)

4. Normalized Databases Normalization
A process of organizing database tables to increase stability through reduced (controlled) data redundancy.
Higher normal forms further restrict how attributes are grouped within records
3NF (Third Normal Form) is the generally accepted, minimum standard for designing a database
Every nonkey field is directly related to only to the entire key field and nothing else
{Emp # (key), Emp Name, Dept Code, Dept Name} is not in 3NF since Dept Name can be derived entirely from dept code (both non-key fields)
{Prod # (key), Prod Name, Qty, Cost, ValueinInventory} is not in 3NF since ValueInInventory is a calculated value (from Qty & Cost)
{RawMat # (key), Prod #, AmtReqrd} is not in 3NF since AmtReqrd is derived from both RawMat# and Prod #

5. Database Terminology Northwind DB tables
Second record or row of Categories table describes condiments
Relationship based on shared data in two tables
Key fields
Records 3, 6 8 are condiments

6. Databases Accessible by VB
VB Native format
Microsoft Jet database engine
Microsoft Access
Jet engine can also access
Excel, dBASE, FoxPro, Lotus, Paradox, text files
VB Professional with Open DataBase Connectivity (ODBC) drivers
Can also access SQL Server, Oracle, and DB2

7. Data Control
Provides access to data stored in databases using any one of three types of Recordset objects:
table
snapshot
synaset
Enables data navigation viewed through bound controls.
Without a Data control, data-bound controls on a form can't automatically access data.
Validate event occurs just before new record becomes current.
data control

8. Data Control Properties
Caption
Text that appears inside the control on the form
Connect
Identifies DBMS source of database (Access)
DatabaseName
Assigns the database filename with path (use dialog)
ReadOnly
Defaults to False & must be set to true if user is not allowed to change contents
RecordSource
Assigns the table or query (view) of the database to be used by the VB program
BOF and EOF
Flags set to true when current record pointer positioned before first record or after last record

9. Data-Bound Controls
Same controls we’ve used thus far with additional properties set
Labels (user cannot change), Textboxes (user can change), Checkboxes (T/F or Y/N), etc.
DataSource
point to database (specify name of data control)
DataField
field name in database table that relates to this
It is possible to navigate data in a database simply by designing a form with the data control and binding data-aware controls to the data control -- no coding is needed!

10. Programming the Data Control
Recordset Object
Defined by setting RecordSource property of data control
Accessing Recordset properties in code
datName.Recordset.Property
Since this represents a value, it can only be part of a statement (e.g., assign it to variable or assign something to it)
Applying methods to Recordset object
datName.Recordset.Method
Since this represents a process, it is written like a statement

11. Recordset Properties Checking the database pointer
datName.Recordset. BOF
Flag that is true when record pointer is before first database record (select previous on first record)
datName.Recordset. EOF
Flag that is true when record pointer is after last database record (select next on last record)
Counting the number of DB records
datName.Recordset.RecordCount
Setting or tracking the current DB record
datName.Recordset.BookMark
Determining if desired record was found
datName.Recordset.NoMatch

12. Recordset Move & Refresh Methods
Navigating DB via Code
Move to next database record
datName.Recordset.MoveNext
Move to last database record
datName.Recordset.MoveLast
Move to previous database record
datName.Recordset.MovePrevious
Move to first database record
datName.Recordset.MoveFirst
Refresh method
Explicitly opens the database
datName.Refresh

13. Adding a First button cmdFirst_Click Move to db record 1 RecNum = 1
End
Move to db record 1
Private Sub cmdFirst_Click()
datEx.Recordset.MoveFirst
lblRecNum.Caption = 1
End Sub

14. Adding a Last button cmdLast_Click Move to last db record
RecNum = RecordCount
End
Move to last db record
Private Sub cmdLast_Click()
datEx.Recordset.MoveLast
lblRecNum.Caption = _
datEx.Recordset.RecordCount
End Sub

15. Adding a Next button Private Sub cmdNext_Click() End Sub
cmdFirst_Click
End
Move to next db record
EOF?
True
False
RecNum=RecNum+1
Display already at end - go to start
Private Sub cmdNext_Click()
datEx.Recordset.MoveNext
If datEx.Recordset.EOF Then
Call MsgBox(“msg”,…)
Call cmdFirst_Click
Else
lblRecNum.Caption = _
CInt(lblRecNum.Caption)+1
EndIf
End Sub

16. Adding a Previous button
cmdPrevious_Click
cmdLast_Click
End
Move to previous db record
BOF?
True
False
RecNum=RecNum-1
Display already at start - go to end
Private Sub cmdPrevious_Click()
datEx.Recordset.MovePrevious
If datEx.Recordset.BOF Then
Call MsgBox(“msg”,…)
Call cmdLast_Click
Else
lblRecNum.Caption = _
CInt(lblRecNum.Caption)-1
EndIf
End Sub

17. Recordset Find Methods
Search for a specific type of record and then move to it in the specified direction.
Specifying search criteria
<DBFieldName> <relational operator> <expression>
Find methods define starting point & search direction
Start at first record and search forwards
datName.Recordset.FindFirst (search criteria)
Start at last record and search backwards
datName.Recordset.FindLast (search criteria)
Start at current record and search forwards
datName.Recordset.FindNext (search criteria)
Start at current record and search backwards
datName.Recordset.FindPrevious (search criteria)

18. Searching Example 1) Save the current record 3) Assign search criteria
CurRecord = datName.Recordset.BookMark
3) Assign search criteria
SearchStr = InputBox(“prompt”, “title”, “default”)
Target = “TableName.FieldName = `” & SearchStr & “`”
3) Use search criteria
Call datName.Recordset.FindFirst(Target)
If datName.RecordSet.NoMatch Then
Call MsgBox(“ERROR”)
Else
‘ whatever processing needs to be done with current record
End If

19. Example: Find similar name
Private Sub cmdFindName_Click()
Dim CurRecord As Variant
Dim SearchString As String
' Save location of current record
CurRecord = datEmployee.Recordset.Bookmark
SearchString = "EmpName Like '" & _
txtSearchName.Text & "*'"
Call datEmployee.Recordset.FindFirst(SearchString)
If datEmployee.Recordset.NoMatch Then
Call MsgBox("No such employee", _
vbOkOnly + vbInformation)
' Move pointer to previously saved location
datEmployee.Recordset.Bookmark = CurRecord
Else
' fill display controls with found record’s data
Call ShowDBData
End If
End Sub

20. Methods to change DB content
Delete current database record datName.Recordset.Delete
be sure to add step to go to a valid record
AddNew database record datName.Recordset.AddNew
clears data bound controls so user can enter new data
DB automatically updated by moving to another record or explicitly saving record
Edit database record datName.Recordset.Edit
moves current DB record to copy buffer to allow changes to occur
Update database with addition datName.Recordset.Update
explicitly saves newly entered data
Reset db to previous values datName.Recordset.UpdateControls
resets data bound controls to previous values

21. Example: Add a new record
Private Sub cmdAddRec_Click()
If cmdAddRec.Caption = "&Add" Then ' 1) Clear input controls
Call DisableNavigation
Call datEmployee.Recordset.MoveLast
txtID.Text = Format(datEmployee.Recordset!empid + 1)
Call datEmployee.Recordset.AddNew
txtEmpName.Text = ""
txtBirthdate.Text = ""
txtPayRate.Text = ""
' Change caption to Save and disable other buttons
cmdAddRec.Caption = "&Save"
Call txtEmpName.SetFocus
Else ' the caption must be &Save ' 2) Write user input to DB
Call WriteDBData
datEmployee.Recordset!empid = txtID.Text
Call datEmployee.Recordset.Update
' Change caption to Add and enable other buttons
cmdAddRec.Caption = "&Add"
Call EnableNavigation
End If
End Sub

22. Example: Delete a record
Private Sub cmdDeleteRec_Click()
Dim CurRec As Variant
CurRec = datEmployee.Recordset.Bookmark ' The record to delete
datEmployee.ReadOnly = False
Call datEmployee.Refresh
Call datEmployee.Recordset.MoveLast
datEmployee.Recordset.Bookmark = CurRec
Call datEmployee.Recordset.Delete
datEmployee.ReadOnly = True
' Move to the last record
Call cmdLast_Click
If datEmployee.Recordset.EOF Then ' Last record was deleted
Call cmdFirst_Click
If datEmployee.Recordset.BOF Then ' No records left
Call MsgBox("There are no records left-the database" & _
" is empty", vbOkOnly + vbInformation)
End If
End Sub

23. Example: Change a record
Private Sub cmdModifyRec_Click()
' The current record will be the one to be modified
If cmdModifyRec.Caption = "&Modify" Then ' 1) Allow edit of record
Call DisableNavigation
Call datEmployee.Recordset.Edit
' Change caption to Save and disable other buttons
Call txtEmpName.SetFocus
cmdModifyRec.Caption = "&Save"
cmdDeleteRec.Enabled = False
cmdAddRec.Enabled = False
Else ' the caption must be &Save ' 2) Copy updates to DB
Call WriteDBData
Call datEmployee.Recordset.Update
' Change caption to Modify and enable other buttons
cmdModifyRec.Caption = "&Modify"
cmdDeleteRec.Enabled = True
cmdAddRec.Enabled = True
Call EnableNavigation
End If
End Sub

24. Preventing Errors Add code to the Validate Event of data control
Add error handlers in all procedures that access DB
Examples:
The primary key must be non-blank
All data entered must be of correct type and length
The database table has valid records (not an empty table)
Pseudocode/Algorithm
If a required field is empty and both BOF and EOF are False Then
Show error msg
Reset error condition so program can run
Don’t save changes
Endif

25. Checking for Empty Recordsets
If BOF and EOF Then
Display error message
End If
By checking for both BOF & EOF, you are checking for a recordset with no members

26. Queries: Joining DB tables
1) Define query to get all unique field names from both tables
Query = “Select * From TableName1, TableName2 Where ” & _
“ TableName1.FieldX = TableName2.FieldY”
Query = “Select TableName1.FieldA, TableName1.FieldB, “ & _
“TableName2.FieldZ Where TableName1.FieldX = “ & _
“TableName2.FieldY”
2) Assign Query to RecordSource property & Open the DB
datName.RecordSource = Query
Call datName.Refresh
3) Start at the first record
Call datName.Recordset.MoveFirst
4) Assign value in current DB field to control on form
lblName.Caption = datName.Recordset(“FieldName”)
lblName.Caption = datName.Recordset!FieldName

27. Filling list with DB field choices
1) Get filename from user (common dialog)
2) Assign user’s file selection to DatabaseName property of data control
3) Define query to get all unique field names
Query = “Select Distinct FieldName From TableName”
datName.RecordSource = Query
4) Use Refresh method to open the database
Call datName.Refresh
5) Clear the list & add any general choices (“Show All”)
6) For each item in the database, add the item to the list and go to next item until done
Call cboName.AddItem(datName.Recordset(”FieldName"))
Call cboName.AddItem(datName.Recordset!FieldName)

28. Returning select DB records
1) Define query using user’s selection
a) General “Show All” choice: Query = “Select * From TableName”
b) Otherwise: Query = “Select * From TableName Where “ & _
“FieldName = `“ & cboName.Text & “`”
2) Assign Query to data control
datName.RecordSource = Query
3) Use Refresh method to open the database
Call datName.Refresh
4) If flexgrid is used on the form, it will automatically contain all fields of the desired records based on the search criteria