Mark Dixon Page 1 18 – Persistent data storage: relational databases and ADO.

Mark Dixon

18 – Persistent data storage: relational databases and ADO

Mark Dixon

Question: Self-Contained

• Are the following routines self contained?Dim g

Dim w

Sub Square(ByRef res As Double, ByVal n1 As Double)

res = n1 * n1

End Sub

Function u(num As Double) As Double

Return num * (w + g)

End Function

Mark Dixon

Session Aims & Objectives• Aims

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

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

– create a relational database table– create a web page (ASP) that displays data

from a single table in a database• using ActiveX Data Objects (ADO)

– use SQL in your programs to create more complex record-sets

Mark Dixon

Persistent Data Storage• So far

– programs (web-pages) 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)

Mark Dixon

Example: People (analysis)SPECIFICATION

• User Requirements – need to have access to people's details

• Software Requirements– Functional:

–Display list of people from a database– Non-functional

should be viewable anywhere in the world

Mark Dixon

Record Field

Example: People (Database)

ID Surname Forenames Phone Gender

1 Dixon Mark 01752 232556 Male

2 Smith John 01752 111111 Male

3 Jones Sally 01752 888888 Female

• Information organised into– tables (e.g. person)– fields (e.g. phone)– records (e.g. 1 Dixon Mark 01752 232556 …)

Person

Mark Dixon

• How many fields?

• How many records?

Questions: Music (Database)

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

9

3

Mark Dixon

DBMS• Database Management Systems (DBMS)

provide 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

Mark Dixon

MS Access

Music database

Mark Dixon

ActiveX Data Objects• 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

Mark Dixon

Using Record Sets

Const cs = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=D:\People.mdb;"Dim rs As Object rs = CreateObject("ADODB.Recordset") rs.Open("Person", cs)

Do Until rs.EOF() … rs.MoveNext() Loop

rs.Close() rs = Nothing

Connection string – identify database

Open record set with table

Move to next record

Close record set

Mark Dixon

ADO Record Set Object• Used to interact with tables• Properties

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

• Methods– Open: used to open record set– 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 record set

Mark Dixon

Connection Strings: UDL files• Generate connection strings

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

– Double click– Select provider (MS Jet 4.0 OLE DB Provider)– Click Next– Select or enter DB name– Click Test Connection button– Click OK– Open with Notepad, cut & paste text

Mark Dixon

People.aspx

Example: People (rs)rs

Sub Page_Load() Const cs = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\People.mdb;" Dim rs As Object Dim s As String rs = CreateObject("ADODB.Recordset") rs.Open("Person", cs) s = "" Do Until rs.EOF() s = s & rs.Fields("Surname").Value & " " rs.MoveNext() Loop parData.InnerHtml = s rs.Close() rs = Nothing End Sub

Mark Dixon

People.aspx

Example: People (s)rs


s

Mark Dixon

People.aspx

Example: People (recordset)rs


s

Mark Dixon

People.aspx

Example: People (Open)rs


s

ID Surname Forenames Phone gender1 Dixon Mark 01752 232556 Male2 Smith John 01752 111111 Male3 Jones Sally 01752 888888 Female

Mark Dixon

People.aspx

Example: Peoplers


s


Mark Dixon

People.aspx

Example: People (EOF)rs


s


Mark Dixon

People.aspx

Example: Peoplers


sDixon

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People.aspx

Example: People (MoveNext)rs


sDixon

Mark Dixon

People.aspx

Example: People (Loop)rs


sDixon

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People.aspx



sDixon

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People.aspx

Example: Peoplers


sDixon Smith Dixon

Mark Dixon

People.aspx



sDixon Smith

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People.aspx





Mark Dixon

People.aspx

Example: Peoplers


sDixon Smith Jones Dixon Smith

Mark Dixon

People.aspx



sDixon Smith Jones

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People.aspx





Mark Dixon

People.aspx

Example: Peoplers


Dixon Smith Jones 

s

Mark Dixon

Example: People v2

Sub Page_Load() Const cs = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\People.mdb;" Dim rs As Object Dim s As String rs = CreateObject("ADODB.Recordset") rs.Open("Person", cs) s = "" Do Until rs.EOF() If rs.Fields("Gender").value = "Male" Then s = s & rs.Fields("Surname").Value & " " End If rs.MoveNext() Loop parData.InnerHtml = s rs.Close() rs = Nothing End Sub

• Display Surname of Male people:

Mark Dixon

Example: People v3• Display Surname of Male people:

Sub Page_Load() Const cs = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\People.mdb;" Dim rs As Object Dim s As String Dim sql As String rs = CreateObject("ADODB.Recordset") sql = "SELECT * FROM [Person] WHERE [Gender] = 'Male';" rs.Open(sql, cs) s = "" Do Until rs.EOF() s = s & rs.Fields("Surname").Value & " " rs.MoveNext() Loop parData.InnerHtml = s rs.Close() rs = Nothing End Sub

SQL statement

Mark Dixon

SQL: Queries• main purpose of databases:

– get information back out: searching

• Structured Query Language– dedicated to interacting with databases

• 3rd Generation Language (such as VB, C++)– code describes how to do task

• 4th Generation Language (such as SQL)– code describes what to do (not how to do it)

Mark Dixon

SQL: SELECT statement• SELECT statement

– used to get data– can be embedded in VB, via rs.Open:

rs.Open("Person", cs)

rs.Open("SELECT * FROM [Person]", cs)

all fields

Mark Dixon

SQL: WHERE & ORDER BY• WHERE clause

– used to restrict data

SELECT * FROM [People] WHERE [age]>=18;

• ORDER BY clause– used to change order of data

SELECT * FROM [People] ORDER BY [Surname];

Mark Dixon

SQL: strings (text data)• Possible confusion:

SELECT * FROM Person WHERE Surname = Smith

this will look for field called Smith - gives error need single (SQL) quotes to signify literal text SELECT * FROM Person WHERE Surname = 'Smith'

Mark Dixon

SQL & MS access queries• MS Access

– Queries: select data from database– really SQL select statements

– can use queries to test SQL code

MS Access: People.mdb

Mark Dixon

Questions: SQL• Create an SQL

statement to extract Track Title of records by Aerosmith




Pink Aerosmith US


Smooth Criminal Alien Ant Farm

US



Voices Disturbed US

Down with the Sickness

Disturbed US

Track

SELECT [Track Title] FROM Track WHERE [Artist Name] = 'Aerosmith';

MS Access: Music.mdb

Mark Dixon

Questions: SQL• Create an SQL

statement to extract all fields of songs by Disturbed, ordered by track name




Pink Aerosmith US


Smooth Criminal Alien Ant Farm

US



Voices Disturbed US

Down with the Sickness

Disturbed US

Track

SELECT * FROM Track WHERE [Artist Name] = 'Disturbed' ORDER BY [Track Title];

MS Access: Music.mdb

Mark Dixon

Example: People v4

• User controls what is displayed:

Mark Dixon

SQL: DISTINCT records

SELECT [Artist Name]FROM [Track];

Artist Name

Black Sabbath

Aerosmith

Aerosmith

Aerosmith

Alien Ant Farm

Disturbed

Disturbed

Disturbed

Disturbed

Artist Name

Black Sabbath

Aerosmith

Alien Ant Farm

Disturbed

SELECT DISTINCT [Artist Name]FROM [Track];

Mark Dixon

Tutorial Exercise: People• Task 1: Create your own People database:

– Open MS Access– Create a new database file– Create a new table– Create fields– Enter data

• Task 2: Get the People v1 example (from the lecture) working.• Task 3: Modify your page so that it displays phone number as well as the

person's name.• Task 4: Modify your page so that it displays the data in an html table.• Task 5: Modify your page so that records for males are displayed in blue, and

records for females are displayed in red.• Task 6: Modify your page as per version 4. You will need to:

– Add a form to the page, and three submit buttons– In your code, detect when a button has been pressed (have a look at

previous weeks)• Task 7: Modify your page so that the user can type a letter, and only names

starting with that letter are displayed.• Task 8: Modify your page so that the user can type a series of numerical digits

and only phone numbers containing those digits are displayed.• Task 9: Modify your code so that the user can order the data by surname, or

email address (You may want to use a Query String)

Mark Dixon Page 1 18 – Persistent data storage: relational databases and ADO.

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