Mark Dixon, SoCCE SOFT 131Page 1 17 – Persistent data storage: relational databases and ADO.

Mark Dixon, SoCCE SOFT 131

17 – Persistent data storage: relational databases and ADO


Session Aims & Objectives• Aims

– To introduce the fundamental ideas involved in persistent data storage and relational databases

• Objectives,by end of this week’s sessions, you should be able to:

– create a relational database– use a relational database to store an

application's data between executions– create an entity-relationship diagram from a

database


Persistent Data Storage• So far

– all programs lose data when closed

• Not realistic– typically data stored to persistent storage device

(e.g. hard disk, key drive, floppy disk, CD-RW)

• Use either– flat files– database (relational, or object oriented)


Record

Field

Flat files: Data Duplication

Track Title Artist Name Country

Paranoid Black Sabbath UK

Falling in Love Aerosmith US

Pink Aerosmith US

Love in an Elevator Aerosmith US

Smooth Criminal Alien Ant Farm US

Meaning of Life Disturbed US

The Game Disturbed US

Voices Disturbed US

Down with the Sickness Disturbed US

Track


Relations (tables)Track Title Artist

ID

Paranoid 1

Falling in Love 2

Pink 2

Love in an Elevator 2

Smooth Criminal 3

Meaning of Life 4

The Game 4

Voices 4

Down with the Sickness 4

Artist ID

Artist Name Country

1 Black Sabbath UK

2 Aerosmith US

3 Alien Ant Farm US

4 Disturbed US

Track

Artist

Primary Key

Foreign Key


Normalisation• Part of database design

• Process of breaking data down

• Codd– 7 stages of normalisation

• Mathematical

• Difficult to apply stages


Exercise: Prescriptions• Identify duplication and separate:

Date Surname Forenames Drug Name

6 Jan 04 Jones Alison Co-codamol

11 Jan 04 Smith Bob Tegretol

18 Jan 04 Hope John Co-codamol

5 Feb 04 Johnson Sally Co-codamol

8 Feb 04 Smith Bob Tegretol

10 Feb 04 Smith Bob Sorbitol

Prescription


Exercise: Solution

Date PatientID DrugID

6 Jan 04 1 1

11 Jan 04 2 2

18 Jan 04 3 1

5 Feb 04 4 1

8 Feb 04 2 2

10 Feb 04 2 3

Prescription

PatientID Surname Forenames

1 Jones Alison

2 Smith Bob

3 Hope John

4 Johnson Sally

Patient

DrugID Drug Name

1 Co-codamol

2 Tegretol

3 Sorbitol

Drug


People Database (with Hobbies)ID Surname Forenames Phone email

1 Dixon Mark 01752 232556 [email protected]

2 Smith John 01752 111111 [email protected]

3 Jones Sally 01752 888888 [email protected]

4 Bloggs Fred 01752 123123 [email protected]

5 Anderson Genny 01752 987987 [email protected]

HobbyID Description PersonID

1 Archery 1

2 Herpetology 1

3 Music 1

4 Football 2

5 Rugby 2

6 Hitting people with swords 1

Hobby

Person


Entity-relationship diagrams• Each table in db

– stores details of entity• shown as rectangular box

•Relationships between tables

–represent relationships between entities

•shown as line between entities (boxes)

Person Hobby


Relationship Types• One-to-one

• One-to-many

• Many-to-one

• Many-to-many– (can't be implemented in relational database)

A B

A B

A B

A B


Exercise: Which relationship type?

ID Surname Forenames Phone email

1 Dixon Mark 01752 232556 [email protected]

2 Smith John 01752 111111 [email protected]

3 Jones Sally 01752 888888 [email protected]

4 Bloggs Fred 01752 123123 [email protected]

5 Anderson Genny 01752 987987 [email protected]

HobbyID Description PersonID

1 Archery 1

2 Herpetology 1

3 Music 1

4 Football 2

5 Rugby 2

6 Hitting people with swords 1

Hobby

Person

Person

Hobby


Database Management Systems• DBMS provides facilities for:

– creating and changing databases• add/remove records• add/remove fields• add/remove data

– For example:• Microsoft Access• dBase• Borland Paradox• MySQL• Microsoft SQL Server• Oracle

home/small business

large scale


MS Access

Music database


ActiveX Data Objects (what & why)

• ActiveX Data Objects (ADO)– common database interface

• allow you to write code for any DBMS

VB orVB Script

codeADO

MS Access

MS SQL Server

…

…DB front end


Enabling ADO• Project menu

– References item• Microsoft ActiveX Data Objects Library (latest 2.7)


ADO RecordSet Object• Used to interact with tables• Properties

– BOF: true if at start of recordset (before first record)– EOF: true if at end of recordset (after last record)– Fields: used to get and set data values

• Methods– Open: used to open recordset– MoveFirst: moves focus to first record– MovePrevious: moves focus to previous record– MoveNext: moves focus to next record– MoveLast: moves focus to last record– Close: closes recordset


Example: Music

Private Sub btnLoad_Click()Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "Track", cs rs.MoveFirst Do Until rs.EOF lstTracks.AddItem rs.Fields("TrackTitle").Value rs.MoveNext Loop rs.Close Set rs = NothingEnd Sub

btnLoad lstTracks


Connection Strings• Connection string – identify data source

Const cs = "Provider=Microsoft.Jet.OLEDB.4.0;" & _ "Data Source=D:\Music.mdb;" & _ "Persist Security Info=False"

Private Sub btnLoad_Click()Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "Track", cs

…

End Sub


UDL files• Generate connection strings

– Right click on desktop– Select New, Text Document– Rename to *.UDL (Yes to warning message)

– Double click– Select provider– Click Next– Select or enter DB name– Click Test Connection button– Click OK– Open with Notepad, cut & paste text


Searching for Data• Recordset methods

– Find: searches for the next record to match given criteria string:

• e.g. "Name = 'Smith' "( " are for VB string)( ' are for database string)


Example: Music v2Private Sub lstTracks_Click()Dim rs As ADODB.RecordsetDim strCriteria As String Set rs = New ADODB.Recordset rs.Open "Track", cs, adOpenDynamic strCriteria = "TrackTitle = '" & _ lstTracks.List(lstTracks.ListIndex) & "'" rs.Find strCriteria txtTrackTitle.Text = rs.Fields("TrackTitle").Value rs.Close Set rs = NothingEnd Sub


Changing Data• Recordset methods

– AddNew: inserts a new record and makes it current

– Update: sends changes back to DB– Delete: deletes currently selected record


Example: Music v3Private Sub txtTrackTitle_Change()Dim rs As ADODB.RecordsetDim strCriteria As String Set rs = New ADODB.Recordset rs.Open "Track", cs, adOpenDynamic, adLockPessimistic strCriteria = "TrackTitle = '" & _ lstTracks.List(lstTracks.ListIndex) & "'" rs.Find strCriteria rs.Fields("TrackTitle").Value = txtTrackTitle.Text rs.Update rs.Close Set rs = NothingEnd Sub

Mark Dixon, SoCCE SOFT 131Page 1 17 – Persistent data storage: relational databases and ADO.

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