Application Programming for Relational Databases Cyrus Shahabi Computer Science Department University of Southern California shahabi usc edu C Shahabi 1 C Shahabi Overview JDBC Package Connecting to databases with JDBC Executing select queries Executing update queries 2 Overview Role of an application Update databases extract info through User interfaces Non interactive programs Development tools Access Oracle C Shahabi For user Interfaces Programming languages C C Java User Interfaces Non Interactive programs More professional 3 Client server architecture Database client C Shahabi Connects to DB to manipulate data Software package Application incorporates software package Client software Provide general and specific capabilities Oracle provides different capabilities as Sybase its own methods 4 Client server architecture Client Server architectures 2 tier 3 tier Layer 1 Layer 2 Middleware Layer 3 user interface DB server Middleware Server for client Client for DB C Shahabi 5 Client server architecture Example Web interaction with DB C Shahabi Layer 1 web browser Layer 2 web server cgi program Layer 3 DB server 6 Client server architecture Application layer 1 User interfaces Other utilities report generator Connect to middleware Can connect to DB too Can have more than one connection Can issue SQL or invoke methods in lower layers Middleware layer 2 C Shahabi More reliable than user applications 7 Database interaction in Access Direct interaction with DB For implementing applications Not professional Developer edition Access application C Shahabi Generates stand alone application GUI Visual Basic for Applications code 8 Database interaction in Access Connection to DB through Microsoft Jet database engine Support SQL access Different file formats Other Database Connectivity ODBC Support SQL DBs Requires driver for each DB server Driver allows the program to become a client for DB C Shahabi Client behaves Independent of DB server 9 Database interaction in Access Making data source available to ODBC application Install ODBC driver manager Install specific driver for a DB server Database should be registered for ODBC manager How application works with data source C Shahabi Contacts driver manager to request for specific data source Manager finds appropriate driver for the source 10 Database interaction in Java Includes Java sql package Set of classes Supports JDBC java database connectivity strategy independent of the DB server Difference between JDBC and ODBC C Shahabi JDBC driver manager is part of the application 11 Database interaction in Embedded SQL Extension of a language C C with new commands Void addEmployee char ssn char lastname char firstname Exec SQL Insert into customer ssn lastname firstname values ssn lastname firstname C Shahabi Not legal language Compilation precedes by a translation preprocessor from embedded SQL into legal C Advantages Disadvantages Not portable between database systems Difficult debugging 12 JDBC Architecture Four Architectural Components C Shahabi Application initiates and terminates connections submits SQL statements Driver manager load JDBC driver Driver connects to data source transmits requests and returns translates results and error codes Data source processes SQL statements 13 JDBC Architecture Contd Four types of drivers Bridge Translates SQL commands into non native API Example JDBC ODBC bridge Code for ODBC and JDBC driver needs to be available on each client Direct translation to native API non Java driver Translates SQL commands to native API of data source Need OS specific binary on each client Network bridge Send commands over the network to a middleware server that talks to the data source Needs only small JDBC driver at each client Direction translation to native API via Java driver C Shahabi Converts JDBC calls directly to network protocol used by DBMS Needs DBMS specific Java driver at each client 14 JDBC package Collection of interfaces and classes C Shahabi DriverManager Loads the driver Driver creates a connection Connection represents a collection DatabaseMetaData information about the DB server Statement executing queries PreparedStatement precompiled and stored query CallableStatment execute SQL stored procedures ResultSet results of execution of queries ResultSetMetaData meta data for ResultSet Reminder Each JDBC package implements the interfaces for specific DB server 15 JDBC different strategies Strategies to USE JDBC JDBC ODBC bridge JDBC database client C Shahabi Con ODBC must be installed Con JDBC driver for each server must be available JDBC middleware client Pro Only one JDBC driver is required Application does not need direct connection to DB e g applet 16 Connecting with JDBC Database connection needs two pieces JDBC package driver class name Package driver provide connection to DB URL of the database JDBC package designator Location of the server Database designator in form of Server name Database name Username password Properties C Shahabi 17 Connecting to DB with JDBC Step 1 Find open and load appropriate driver 1 Class forName sun jdbc odbc JdbcOdbcDriver 2 Class forName oracle thin Driver 3 Class forName symantec dbAnywhere driver Or C Shahabi 4 DriverManager registerDriver your jdbc driver Informs availability of the driver to DriverManager registers the driver with DriverManager Example 1 18 Connecting to DB with JDBC Step 2 Make connection to the DB Connection conn DriverManager URL Properties Properties specific to the driver URL Protocol user Protocol jdbc subprotocol subname E g jdbc odbc mydatabase E g jdbc oracle thin oracle cs fsu edu bighit C Shahabi Example 1 19 Connecting to DB with JDBC Step 3 Make Statement object Used to send SQL to DB executeQuery SQL that returns table executeUpdate SQL that doesn t return table Execute SQL that may return both or different thing Step 4 obtain metadata optional DatabaseMetaData object getTimeDatefunctions all date and time functions C Shahabi Example 2 20 Executing select queries Step 5 issue select queries Queries that return table as result Using statement object Uses executeQuery method Return the results as ResultSet object Every call to executeQuery deletes previous results C Shahabi Meta data in ResultSetMetaData object Example 2 21 Executing select queries Step 6 retrieve the results of select queries Using ResultSet object Returns results as a set of rows Accesses values by column name or column number Uses a cursor to move between the results