Connecting to a Database through Programs

Database Systems

DB Connections

• Typically only DBA ‘talk’ directly to a database

• End users generally connect to a database through some type of program– Program code– Forms

Connection Part 1

• Database tables are not ‘part’ of a program– So you have to establish a connection to them

• Connections are categorized in 2 categories– READ– Insert, Update and Delete

Not all DBs are Alike

• Not all databases act the same way, you have to know which way your database acts

• This determines the facilities needed for your connection

• Then you have to remember that relational database systems speak SQL

Connection Introduction

• Because database applications today reside in a complicated environment, various standards have been developed for accessing database servers.

• Some of the important standards are– OBDC (Open Database Connectivity) is the early standard for

relational databases.– OLE DB is Microsoft’s object-oriented interface for relational and

other databases.– ADO.NET (Active Data Objects) is Microsoft’s standard

providing easier access to OLE DB data for the non-object-oriented programmer.

The Role of the ODBC Standard

Open Database Connectivity (OBDC)

• The Open Database Connectivity (ODBC) standard provides a DBMS-independent means for processing relational database data.

• It was developed in the early 1990s by an industry committee and has been implemented by Microsoft and many other vendors.

• The goal is to allow a developer to create a single application that can access databases supported by different DBMS products without needing to be changed or recompiled.

ODBC Architecture

OBDC Components (Continued)

• OBDC consists of a data source, an application program, a driver manager, and a DBMS driver.

• A data source is the database and its associated DBMS, operating system, and network platform.– An ODBC data source can be a relational database, a

file server, or a spreadsheet.

• An applications program issues requests to create a connection with a data source.

OBDC Components

• A driver manager determines the type of DBMS for a given ODBC data source and loads that driver in memory.

• A DBMS driver processes ODBC requests and submits specific SQL statements to a given type of data source.

Conformance Levels

• Levels of conformance balance the scope of the OBDC standard.

• There are two types of conformance levels:– ODBC conformance levels concern the features and

functions that are made available through the driver’s application program interface (API).

• A driver API is a set of functions that the application can call to receive services.

– SQL conformance levels specify which SQL statements, expressions, and data types a driver can process.

Summary ofOBDC Conformance Levels

Summary ofSQL Conformance Levels

So, why do conformance levels matter?

You pick the ODBC driver you use based on your needs

How do you connect?

• Depends on the database and the programming environment

• Access can establish a DNS so that Access may be used as a front end to a database (ie front end to an oracle db)

• Java establishes a ODBC connection via the JDBC library

• C#, VB.Net use a Microsoft provided ‘Managed Provider’, ADO.Net or OBDC

The Steps whatever the case

• Establish a connection• Open the connection• Select data using an Object with SQL statement• Retrieve the Data

– Data is not used directly from the database – Retrieved into hold place such as a variable or object– Display the data

• OR Issue a Insert, Update or Delete command– Send data to the database– Usually number of rows affected is returned

Example

• Sample Code– http://science.kennesaw.edu/~mcmurray/dbTa

bles/labjava/Customers.java

• JDBC walkthrough– http://www.javacoffeebreak.com/articles/jdbc/i

ndex.html

Where does the data go?

• Insert, Update, Delete– Pushing data out to the Database– What is returned is the number of rows

affected

• What happens when you read [select] data?– Somehow you have to store the data in

memory

Data retrieval

• How much data are you retrieving?– One row – it’s fairly trivial

• Use variables

– Lots of Rows• Considerations to make and it will depend on the

technology being used

Cursor

• Used by Oracle PL/SQL is known as ‘cursor’

– Way data is accessed row by row

– Can be utilized in Java

Example

• To retrieve data with SQL one row at a time you need to use cursor processing.

• Cursor processing is done in several steps:1. Define the rows you want to retrieve. This is called

declaring the cursor. 2. Open the cursor. This activates the cursor and loads

the data. • Note that declaring the cursor doesn't load data, opening

the cursor does.

3. Fetch the data into variables. 4. Close the cursor.

http://www.fluffycat.com/SQL/Cursor-Oracle/

Cursor References

• http://www.exforsys.com/tutorials/oracle-9i/oracle-cursors.html

• http://www.oracle.com/technology/documentation/berkeley-db/je/GettingStartedGuide/Cursors.html

.NET

• Microsoft’s .NET uses– Datareader

• Processing row by row

– Datasets• Declared space in memory (data structure that

looks like a table)• Defined using XML schema• Loads all results of select statements into memory

for processinghttp://quickstart.developerfusion.co.uk/quickstart/howto/doc/adoplus/GetDataFromDB.aspx

Labs

• ACCESS connecting to Oracle– http://aspalliance.com/893_Creating_an_MS_Access

_2003_Front_End_for_an_Oracle_10g_Express_Edition_Database

• ADO.Net using Visual Studio (for IS and ISA majors)– Need an Oracle Managed Provider

• One is includes with Visual Studio but many problems reported so need to get one from Oracle

• Oracle 11g is has managed provided for ADO.Net built in

• JDBC for CS majors

SOME JAVA Examples

• http://java.sun.com/developer/codesamples/jdbc.html

• http://www.cs.ubc.ca/~ramesh/cpsc304/tutorial/JDBC/jdbc1.html

• http://java.sun.com/j2se/1.3/docs/guide/jdbc/getstart/GettingStartedTOC.fm.html

• http://www.jdbc-tutorial.com/• http://www.javacoffeebreak.com/articles/

jdbc/index.html

Some MySQL PHP Resources• Connecting to a MySQL database via PHP

– http://www.php-mysql-tutorial.com/connect-to-mysql-using-php.php

– http://dev.mysql.com/tech-resources/articles/ddws/21.html

• Resources for graphical support of forms development PHP– http://phpmyadmin.qarchive.org/

• MySQL with JDBC– http://www.developer.com/java/data/article.php/3417381