Connecting to Databases

connecting to DB DB server typically a standalone application Server runs on localhost for smaller sites –i.e. Same machine as web server Separate machine for larger sites DB server examples: –MySQL, PostgreSQL - free –SQL Server, Oracle - commercial

relational databases tables and relations accessed using SQL database -specific functionality –transaction processing commit and rollback –different SQL dialects –auto-numbered table rows –programming

connection technologies ODBC –Access, SQLServer, most databases have an ODBC interface –Excel, CSV files JDBC –most databases have JDBC drivers OLE DB –Windows only specific database drivers client libraries –database specific APIs

common tasks locking mechanisms –exclusive locks –read-only (sharing) locks) database connection –data source name (DSN) –userID –password

common tasks query the database retrieve a result set process the result set error handling release resources

Database Connectivity with Perl CGI

DBM files classic Perl data format essentially persistent associative arrays –elements are key-value pairs look up values using keys perform efficient insertion/deletion of values

DBM Example File1.pl dbmopen(%vals,"test.db",0666) || die("Can't open DB!"); $vals{'name1'}="Douglas"; $vals{'name2'}="Adams"; dbmclose(%map); File2.pl dbmopen(%vals,"test.db",0666) || die("Can't open DB!"); print $vals{'name1'}; print $vals{'name2'} dbmclose(%map);

CSV files Comma Separated Value text format use DBI module with DBD:CSV module allows SQL manipulation of CSV files only simple queries possible slower than conventional text processing good prototyping approach before moving to an RDBMS

Perl DBI module abstract set of tools to interact with (relational) databases uses database specific drivers (DBD) to implement commands –DBD modules DBD:ODBC DBD:Oracle DBD:CSV etc

interaction with databases prepare –parse SQL –validate SQL –create a statement handle execute –passes statement to database –database constructs query results

interaction with databases fetch –query results pulled into Perl data structures –processing then carried out on fetched data deallocation –release of database resources at end of processing –clears memory, removes any locks –handled automatically

Example... use DBI; my $db = DBI->connect ("dbi:Oracle:fridge", "user", "pass"); my $sql = $db->prepare ("SELECT * FROM FREEZER"); = $sql->fetchrow_array();...

summary of Perl DBI powerful approach DBD modules available for most databases available on most platforms –compatibility problems with different Perl versions CGI not suitable for high-end systems –speed and security problems flock command –exclusive locks or sharing locks –resources released when filehandles are destroyed

database connectivity with PHP

database-specific extensions written in C++ non-portable –bound to one database pg_query(…) fast –optimised to database support all functionality non-standard interface significant code-rewriting to change database frameworks like Cake help

PEAR DB Library database independent abstraction layer provided as standard with PHP sits on top of DB client libraries code more portable to other databases supports only standard DB functionality runs slightly slower than specific extensions

Example <?php require_once ('DB.php'); $db = DB::connect $sql = "SELECT * FROM FREEZER"; $q = $db->query ($sql); while ($q->fetchInto($item)) {... } ?>

PHP with PEAR DB powerful approach current technology of choice for small to mid- size 3-tier systems easy to implement portable across different platforms specific extensions can optimise performance limited use for high-end applications –because of general PHP scaleability issues

database connectivity with JSP and servlets

JDBC Java API for Databases –packaged with Java Enterprise interacts with three major database architectures –relational main design focus of JDBC –object-oriented data and methods bundled together in a class hierarchy –object-relational

JDBC advantages –object to relational mapping –tables become objects with standard properties and methods –database independence –full Java support for distributed computing

JDBC driver types Type 1 –bridges to client libraries –requires client software example:JDBC-ODBC bridge Type 2 –native API drivers –JDBC driver calls native methods –native methods provided by database vendors –requires client software

JDBC driver types Type 3 generic client API uses sockets to call database-specific middleware most flexible can provide simultaneous access to multiple databases

JDBC driver types Type 4 database specific, but networked talk directly to database using sockets use proprietary network protocols almost never documented purchased directly from database vendors

Example public class Fridge { public static void main(String [] args) { String url = "jdbc:msql://fridge.com/fridge"; Connection db = null;... try { db = DriverManager.getConnection (url,"user","pass"); Statement sql = db.createStatement ();

Example String query = "SELECT * FROM FREEZER"; ResultSet r = sql.executeQuery (query); while (r.next()) { … // do some stuff } catch(Exception e){e.printStackTrace ();} try {db.close ();} catch(Exception e){e.printStackTrace ();} }

summary of JDBC integrates well with JSP/servelet programming full power of Java programming robust error and exception handling suitable for mid-to-high-end 3- and multi-tier systems –too sophisticated for simpler systems useful tools to ease development –IDEs: NetBeans, Eclipse –Jakarta Turbine

database connectivity with ASP

ADO ActiveX Data Objects provide an API for accessing databases use OLE DB, ODBC Windows platform specific ASP processor creates standard objects to manipulate and retrieve data –Command, Connection, Recordset, Record, Field, Error, Parameter, Property, Stream

Example <% Set db = Server.CreateObject ('ADODB.Connection') str = "driver=MySQL; ; uid='user'; pwd='pass'; database=Fridge" 'open the connection. db.Open str 'create a recordset Set r = Server.CreateObject ('ADODB.Recordset')... continued...

Example... continued... 'construct the SQL for the query sql = "SELECT * FROM FREEZER" 'get the data into the recordset r.Open sql, db... 'release resources Set r = Nothing Set db = Nothing %>

summary of ASP and ADO powerful set of tools platform specific (Windows) versioning incompatibilities –different versions of Windows –different versions of ADO difficult to use –improved under.NET framework not worth the effort for low-end systems –PHP a better choice

database connectivity with ColdFusion

ColdFusion database connection through CFQUERY tag –ODBC most databases standard functionality only –OLE DB (Windows only) Access and SQL Server as standard others available –Native drivers database specific database-specific extensions –not portable

CFQUERY syntax <CFQUERY NAME = "query_name" DATASOURCE = "datasource_name" DBTYPE = "dbtype" CONNECTSTRING = "connection_string" > SQL statements Accessed with

Example <CFQUERY NAME = "fridge_query" DATASOURCE = "Fridge" DBTYPE = "ODBC" CONNECTSTRING = "DRIVER=MicroSoft Access Driver (*.mdb);DBQ=D:\dbfiles\Fridge.mdb;FIL=MSAccess ;UID=user;PWD=pass" > SELECT * FROM FREEZER

summary of ColdFusion approach powerful tag-based DB interface no DB-specific knowledge required wide range of databases supported good for medium to high end systems data locking through CFLOCK