Beginning Web Development With Perl : From Novice to ... - Nabo

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50CHAPTER 3 ■ DATABASES AND PERLThe DBI loads one or more database drivers (generally referred to as DBD, for databasedependent). The DBD, which will be discussed shortly, has the specific software and coderequired to access a given type of database. It provides the interface between the DBI and thetype of database for the connection.Without a DBD, the DBI in and of itself isn’t terribly useful. However, the DBI providesthe methods that you use to work with the database itself. When coupled with the appropriateDBD, the DBI is the key to making database connections work.The DBI gives you three objects, called handles, that enable you to work with the database.These are the driver, database, and statement handles. Driver handles are not commonly usedwithin a CGI program, and will not be discussed here. Database handles are used within a programin order to make a connection to the database. Statement handles are children of databasehandles that are used to send SQL statements to the database. These two types of handles arediscussed in detail later in this chapter, in the “Database Handles” and “Statement Handles”sections.Database DriversA database driver provides the database-interaction methods that are specific to the individualdatabase implementation. It is commonly referred to as the DBD, for database dependent,since its code depends on which database is being used. For example, a MySQL database hasdifferent syntax than an Oracle database. The DBI operates independently of the database,leaving the implementation-specific bits to the DBD.You might be curious as to which drivers are installed on your server. The DBI module providesa function for listing all of the currently installed drivers. Listing 3-1 uses the available_drivers()function of the DBI module to retrieve the drivers available on the server.Listing 3-1. Listing Currently Installed Drivers#!/usr/bin/perluse strict;use DBI;my @drivers;@drivers = DBI->available_drivers();foreach my $dbd (@drivers) {print "$dbd driver is available\n";}exit;You run this program from the command line. The output will look something like this:ExampleP driver is availableProxy driver is availablemysql driver is available
CHAPTER 3 ■ DATABASES AND PERL 51The program incorporates the DBI into the namespace with this line:use DBI;The available drivers are placed into an array called @drivers with this line:@drivers = DBI->available_drivers;Finally, the array is expanded within the foreach loop and printed to STDOUT, producingthe output.As you saw from the output, the MySQL DBD is installed on this server. If you wanted toconnect to a different type of database, you would need to obtain the DBD module from yourfavorite CPAN mirror or install it from your distribution’s repository. For example, Debian 3.0includes a number of DBDs, a listing of which is available by searching the repository with thecommand apt-cache search dbd.Some of the more popular DBDs include the following:• MySQL: As previously stated, MySQL is one quarter of the prized LAMP (Linux-Apache-MySQL-Perl) development platform that’s so popular around the world.• PostgreSQL: Another popular open-source database is PostgreSQL. The DBD forPostgreSQL is similar to that of MySQL.• ODBC: The ODBC DBD is commonly used to connect to databases that run on Windowssystems, such as Microsoft SQL Server and Microsoft Access, but the ODBC driver couldbe used to connect to virtually any database that offers ODBC connectivity.• Sybase: Another popular DBD is used with the Sybase database server. This server andthe DBD for it won’t be covered in this book. For more information about runningSybase on Linux and the DBD for Sybase, see http://www.peppler.org/.Data Source Names, Credentials, and AttributesA data source name, or DSN for short, is the information needed by the DBI in order to connectto the database. This information includes the DSN itself, as well as other informationsuch as the hostname of the server hosting the database, the name of the database, a portnumber, and so on. The exact information that you must supply depends on the DBD thatyou’re using to connect. For example, an Oracle DBD might require or accept differentparameters than the MySQL DBD uses.The DSN is a simple string, frequently stored in a variable called $dsn. DSNs begin withthe characters dbi:, followed by the name of the driver. For example, the DSN for a MySQLdatabase is dbi:mysql. You can expand the code in Listing 3-1 to show the valid DSNs for thegiven database drivers on your system by using the data_sources() DBI method, as shown inListing 3-2.Listing 3-2. Listing Valid DSNs#!/usr/bin/perluse strict;use DBI;
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Beginning Web Development with Perl
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PART 5 ■ ■ ■ Creating Web Tem
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■CONTENTSvii■CHAPTER 4 System I
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■CONTENTSixCreating a SOAP Listen
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■CONTENTSxiTemplate Toolkit Synta
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About the Author■STEVE SUEHRING i
Page 16 and 17: AcknowledgmentsThanks to James Lee
Page 18 and 19: xx■INTRODUCTIONThis book will use
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Page 104 and 105: CHAPTER 5■ ■ ■LWP ModulesLWP
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108CHAPTER 6 ■ NET:: TOOLSCreatin
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110CHAPTER 6 ■ NET:: TOOLSThe out
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112CHAPTER 6 ■ NET:: TOOLSmy $pop
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114CHAPTER 6 ■ NET:: TOOLSthe POP
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116CHAPTER 6 ■ NET:: TOOLS($messa
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118CHAPTER 6 ■ NET:: TOOLSListing
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120CHAPTER 6 ■ NET:: TOOLSFor the
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122CHAPTER 6 ■ NET:: TOOLSNet::SM
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124CHAPTER 6 ■ NET:: TOOLS$smtpco
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126CHAPTER 6 ■ NET:: TOOLSuse Net
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128CHAPTER 6 ■ NET:: TOOLSListing
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130CHAPTER 6 ■ NET:: TOOLSFor exa
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132CHAPTER 6 ■ NET:: TOOLSSending
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PART 3■ ■ ■XML and RSS
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138CHAPTER 7 ■ SOAP-BASED WEB SER
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154CHAPTER 8 ■ PERL AND RSSFigure
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156CHAPTER 8 ■ PERL AND RSShttp:/
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158CHAPTER 8 ■ PERL AND RSSDebugg
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160CHAPTER 8 ■ PERL AND RSS$rsswr
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162CHAPTER 8 ■ PERL AND RSSListin
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CHAPTER 9■ ■ ■XML Parsing wit
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CHAPTER 9 ■ XML PARSING WITH PERL
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PART 4■ ■ ■PerformanceEnhance
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184CHAPTER 10 ■ APACHE AND MOD_PE
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202CHAPTER 11 ■ DEVELOPMENT WITH
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CHAPTER 12■ ■ ■The Template T
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CHAPTER 12 ■ THE TEMPLATE TOOLKIT
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CHAPTER 13■ ■ ■Perl Web Sites
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CHAPTER 13 ■ PERL WEB SITES WITH
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284APPENDIX ■ PERL BASICSKeywords
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286APPENDIX ■ PERL BASICS$ perl n
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288APPENDIX ■ PERL BASICSAnd line
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290APPENDIX ■ PERL BASICSCan you
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292APPENDIX ■ PERL BASICSBy defau
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294APPENDIX ■ PERL BASICS#!/usr/b
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296APPENDIX ■ PERL BASICSThe last
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298APPENDIX ■ PERL BASICSThe NOT
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300APPENDIX ■ PERL BASICSprint "S
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302APPENDIX ■ PERL BASICSthe syst
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304APPENDIX ■ PERL BASICS$ perl s
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306APPENDIX ■ PERL BASICSThis cod
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308APPENDIX ■ PERL BASICS$a = 6 *
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310APPENDIX ■ PERL BASICS$a = "A9
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312APPENDIX ■ PERL BASICS#!/usr/b
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314APPENDIX ■ PERL BASICSmy $name
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316APPENDIX ■ PERL BASICSis short
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318APPENDIX ■ PERL BASICSLet’s
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320APPENDIX ■ PERL BASICSOther Te
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322APPENDIX ■ PERL BASICS}}}actio
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326APPENDIX ■ PERL BASICSLooping
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328APPENDIX ■ PERL BASICSuse stri
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330APPENDIX ■ PERL BASICSuntil ($
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332APPENDIX ■ PERL BASICSuse stri
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334APPENDIX ■ PERL BASICSdoneAll
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336APPENDIX ■ PERL BASICS$ perl r
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338APPENDIX ■ PERL BASICSSummaryT
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340■INDEXmethods for retrieving r
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342■INDEXdo() method for, 62dumpi
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344■INDEXhello option for Net::SM
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346■INDEXNet::DNS module, 125-128
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348■INDEXrecord with Net::DNS mod
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350■INDEXstoring mail server in e
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352■INDEXlogging based on, 229pri
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