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27/07/2001 Copyright 2001, Munica Corporation, 1 How to write a DBD driver Daini Xie Strathy President Munica Corporation

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Presentation on theme: "27/07/2001 Copyright 2001, Munica Corporation, 1 How to write a DBD driver Daini Xie Strathy President Munica Corporation"— Presentation transcript:

1 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 1 How to write a DBD driver Daini Xie Strathy President Munica Corporation dainix@munica.com Presentation for the O’Reilly Open Source Convention 2001 San Diego, CA, USA AMDG

2 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 2 Introduction You will learn the elements of a DBD driver and the process of developing one Audience: DBMS developers and Perl developers Prerequisite: Proficiency in Perl, C and SQL

3 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 3 Agenda Introducing DBI5 min Dissecting DBD10 min Writing a DBD Driver25 min Questions5 min

4 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 4 Overview Introducing DBI: Introduces DBI and prepares you for DBD driver development Dissecting DBD: Explains DBD driver deliverables, objects and interfaces Writing a DBD Driver: Details the driver development process

5 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 5 Acronyms PerlPractical Extraction and Report Language DBI Perl Database Interface DBD Perl Database Driver SQLStructured Query Language XSPerl eXternal Subroutine APIApplication Programming Interface PODPlain Old Documentation, a Perl documentation format

6 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 6 What is DBI? DBI is the Perl Database Interface module written by Tim Bunce DBI provides Perl developers a standard interface for accessing databases

7 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 7 Life without DBI Postgres API NetSQL API Oracle API Postgres engine NetSQL engine Oracle engine Perl Scripts

8 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 8 Life with DBI Perl Scripts DBI DBD::Pg DBD::NetSQL DBD::Oracle Postgres engine NetSQL engine Oracle engine

9 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 9 What is a DBD Driver? DBD stands for Database Driver A DBD driver implements the methods defined in the DBI specification with DBMS specific API

10 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 10 DBI Sample Code 1: use DBI; # Load DBI module 2: 3: my $dbh = DBI->connect('DBI:Pg:dbname=payroll‘, ‘’, ‘’) 4:or die "Couldn't connect to database: ". DBI->errstr; 5: 6: my $sth = $dbh->prepare(‘SELECT * FROM people’) 7: or die “Couldn’t prepare statement: ". $dbh->errstr; 8: 9: $sth->execute() or die "Couldn't execute statement: ". $sth->errstr; 10: 11: while ( @data = $sth->fetchrow_array ) { # fetch the selected row 12:print “@data\n”; 13: } 14: 15: $sth->finish; 16: $dbh->disconnect;

11 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 11 Script/DBI/DBD Interaction DBD Driver DBI Perl Scripts DBI->connect $dbh->prepare $sth->execute $sth->fetchrow_array $sth->finish $dbh->disconnect

12 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 12 Writing a DBD Driver Before you start Conventions and deliverables Driver development to-do list DBD driver objects and interface

13 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 13 Before you start Download and install the latest Perl, the DBI module and Unix utilities such as tar and gzip on your host computer. Decide what kind of DBD driver you’d like to write: –Pure Perl DBD driver –C/XS DBD driver if you require C libraries

14 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 14 DBD Driver Package The set of files that comprises a DBD driver distribution package Perl DriverC/XS Driver Driver.pm Makefile.PL README MANIFEST Driver.pm Makefile.PL Driver.xs Driver.h dbdimp.h dbdimp.c README MANIFEST

15 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 15 DBD Driver Files Driver.pm and Driver.so are the DBD driver files. Pure Perl DriverC/XS Driver Driver.pm Driver.so or Driver.dll

16 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 16 DBD Directory Structure Perl Lib DBD Driver.pm auto DBD Driver.so /usr/lib/perl5/site_perl/5.6.0/i386-linux

17 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 17 Driver Development To-do List 1. Prepare Makefile.PL 2a. Write Driver.pm for a Perl DBD driver or 2b. Write a C/XS DBD driver 2b.1 Write Driver.pm 2b.2 Write Driver.so or its Win32 equivalent Driver.dll 2b.1.1 Write dbdimp.c and dbdimp.h 2b.1.2 Write Driver.xs and Driver.h 3. Finishing touch: README and MANIFEST 4. Building a distribution package

18 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 18 Makefile.PL Makefile.PL is a Perl script that generates Makefile for a DBD driver. Checks the prerequisites of the host environment Checks package integrity Preprocesses, compiles, links and installs files

19 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 19 Makefile.PL Samples Pure Perl DriverC/XS Driver DBD::CSVDBD::Pg or DBD::Oracle Both drivers are available at http://www.cpan.org

20 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 20 Dissecting a DBD Driver package DBD::Driver; package DBD::Driver:dr; package DBD::Driver::db; package DBD::Driver::st;

21 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 21 DBD::Driver DBD::Driver is the class for DBD driver. It holds driver specific data and is responsible for the initialization of the DBD driver. Private Data Members: $VERSION, $err, $errstr, $drh Method: driver

22 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 22 DBD::Driver::dr DBD::Driver::dr is the class for DBD driver handle objects. It holds driver specific data and is responsible for connecting to a given DBMS engine. Private Data Member: imp_data_size Method: connect, disconnect_all, DESTROY

23 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 23 DBD::Driver::db DBD::Driver::db is the class for database handle objects. It holds database specific data and controls the connection and transactions made with a given database. Private Data Member: imp_data_size Methods: prepare, _login, ping, FETCH, STORE, table_info, tables, table_attributes, commit, rollback, type_info_all, disconnect, DESTROY

24 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 24 DBD::Driver::st DBD::Driver::st is the class for statement handle objects. It holds SQL statement specific data and is responsible for parsing, executing and data retrieval of a given SQL statement Private Data Member: imp_data_size Methods: _prepare, FETCH, STORE, bind_param, execute, fetchrow_arrayref, rows, finish, DESTROY

25 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 25 Storing and Retrieving Attributes DBI attributes: Name, Statement, … Driver specific attributes $sth->STORE(‘Statement’, $sqlstr); $sth->FETCH(‘Statement’); Pure Perl Driver: $sth->{‘Statement’} = $sqlstr; C/XS Driver: stored in imp_xxh_t data structures

26 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 26 DBI/DBD Naming Conventions ConventionPertains to UPPER_CASEStandards, e.g. X/Open, ISO SQL 92, etc. (portable) MixedCaseDBI API (portable), underscores are not used lower_caseDriver or database specific (non-portable) _lower_caseInternal DBD methods Private attribute names are prefixed with the driver name or suitable abbreviation (e.g. ora_ for Oracle)

27 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 27 Writing a Pure Perl Driver Set imp_data_size of DBD::Driver::dr, DBD::Driver::db and DBD::Driver::st to zero. Implement the required methods in DBD::Driver, DBD::Driver::dr, DBD::Driver::db and DBD::Driver::st packages. (See slides #21 - #24) In Driver.pm:

28 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 28 Example: DBD::Driver::dr 1: package DBD::Driver::dr; # ==DRIVER=== 2: use strict; 3: 4: $DBD::Driver::dr::imp_data_size = 0; 5: 6: sub connect ($$;$$$) { 7: # insert code to create a $dbh handle 8: } In Driver.pm

29 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 29 C/XS Driver Development Driver.xs Driver.c xsubpp dbdimp.c driver.lib Driver.so Driver.pm otherc.lib Files you implement Files generated by Makefile C libraries used by the driver dbdimp.h

30 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 30 Writing a C/XS Driver DBD::Driver is usually implemented in Perl Part or all of DBD::Driver::dr, DBD::Driver::db and DBD::Driver::st are implemented as Perl external subroutines (XS) and C code

31 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 31 Example: DBD::Pg::st {package DBD::Pg::st; # ===statement# # all implemented in XS } When a Perl method is implemented in Driver.xs and dbdimp.c, it is absent from Driver.pm In Driver.pm

32 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 32 Implementing Perl methods with C/XS Step 1: Define private data structures for DBD::Driver::dr, DBD::Driver::db and DBD::Driver::st Step 2: Implement the required DBD methods in C and place them in dbdimp.c Step 3: Provide an XS Perl wrapper for each method and place it in Driver.xs

33 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 33 Defining Private Data Structures 1: struct imp_drh_t { 2: dbih_drc_tcom; 3: /* insert your driver handle attributes here*/ 4: }; 5: struct imp_dbh_t { 6: dbih_dbc_tcom; 7: /* insert your database handle attributes here*/ 8: }; 9: struct imp_sth_t { 10: dbih_stc_tcom; 11: /* insert your statement handle attributes here*/ 12: }; In dbdimp.h

34 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 34 Example: DBD::Driver::st 1: int dbd_st_execute(SV * sth, 2: imp_sth_t * imp_sth) 3: { 4: /* insert your code here*/ 5: } In dbdimp.c:

35 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 35 Example: DBD::Driver::st 1: MODULE = DBD::Driver PACKAGE = DBD::Driver::st 2: 3: void execute (sth, …) 4: SV * sth; 5: CODE: /*C code fragment*/ 6: D_imp_sth(sth); /*extract imp_sth_t*/ 7: 8: ret = dbd_st_execute(sth, imp_sth); 9: 10: if (ret == 0) { XST_mPV(0, “0E0”);} 11: else if (ret < -1) { XST_mUNDEF(0);} 12: else { XST_mIV(0, ret);} In Driver.xs

36 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 36 Passing data between C and Perl How to pass Perl arguments to C functions How to return data from C functions to Perl

37 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 37 Passing arguments between C and Perl in Driver.xs XS Perl $sth->execute($v1, $v2);void execute (sth, …) SV * sth; CODE: /*C fragment*/ SV *v1, *v2; v1 = ST(1); v2 = ST(2);

38 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 38 Return data from C to Perl in Driver.xs $sth->fetchrow_arrayref(); 1: void fetchrow_arrayref(sth) 2: SV * sth; 3: CODE: 4: D_imp_sth(sth);/*get imp_data_t */ 5: AV *av = dbd_st_fetch(sth, imp_sth); /*get row array*/ 6: /* set the return value to array reference */ 7: ST(0) = (av) ? 8: sv_2mortal(newRV_inc((SV *)av)) :&sv_undef;

39 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 39 Return an array from C to Perl $sth->fetchrow_array(); 1: void fetchrow_arrayref(sth) 2: SV * sth; 3: PPCODE: /*because we need to extend stack*/ 4: D_imp_sth(sth);/*get imp_data_t*/ 5: AV *av = dbd_st_fetch(sth, imp_sth); /*get row array*/ 6: int I, num_fields; 7: if (av) {/*push an SV to the argument stack*/ 8: num_fields = AvFill(av) + 1; 9: EXTEND(sp, num_fields); 10: for (I = 0; I< num_fields; ++i) { 11: PUSHs(AvARRAY(av)[I]); 12: } 13: }

40 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 40 Elements in Driver.xs Slide 1 1: DBISTATE_DECLARE; 2: MODULE=DBD::Driver PACKAGE=DBD::Driver 3: PROTOTYPES: DISABLE# disable Perl prototype 4: BOOT:# initialization 5: DBISTATE_INIT;# initialize DBI 6: 7: DBI_IMP_SIZE(“DBD::Driver::dr::imp_data_size”, 8: sizeof(imp_drh_t)); 9: DBI_IMP_SIZE(“DBD::Driver::dr::imp_data_size”, 10: sizeof(imp_drh_t)); 11: DBI_IMP_SIZE(“DBD::Driver::dr::imp_data_size”, 12: sizeof(imp_drh_t)); 13: 14: dbd_init(DBIS);/*Initialize DBI state*/ … next slide

41 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 41 Elements in Driver.xs Slide 2 15: MODULE = DBD::Driver PACKAGE = DBD::Driver::dr 16: # XS Perl wrappers for C methods, see slides #33 - #38 17: 18: MODULE = DBD::Driver PACKAGE = DBD::Driver::db 19: # XS Perl wrappers for C methods, see slides #33 - #38 20: 21: MODULE = DBD::Driver PACKAGE = DBD::Driver::st 22: # XS Perl wrappers for C methods, see slides #33 - #38

42 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 42 Finishing Touch Document installation related information in the README file Document your DBD driver in POD format and append it at the end of Driver.pm List every file that comprises your driver distribution package, one per line, in the MANIFEST file

43 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 43 Building a distribution package Place all the files that comprise your driver distribution package in a directory, say /mydriver Change directory to /mydriver Use the following command to create an archive: make dist (for Unix) nmake dist (for Win32 with VC++)

44 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 44 Building and Installing Unpack the downloaded DBD driver with the following command: tar –zxvf DBD-Driver-1.0.tar.gz Build and install the driver with the following commands: UNIXWindows with VC++ perl Makefile.PL make make install perl Makefile.PL nmake nmake install

45 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 45 Summary You just learned: –the elements in a DBD driver –the process of developing one –using XS to develop Perl external subroutines for your DBD driver

46 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 46 Where to Get More Information Books (from O’Reilly Associates) Programming Perl Advanced Perl Programming for information about object oriented Perl programming and C/XS development Perl DBI for information about DBI programming

47 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 47 Where to Get More Information Web sites: http://supportweb.cs.bham.ac.uk/documentati on/perl-modules/Informix/DBD.html for DBD Driver Writer’s Guide http://supportweb.cs.bham.ac.uk/documentati on/perl-modules/Informix/DBD.html http://www.munica.com/dbd/dbdtmpl.html for DBD driver development templates http://www.munica.com/dbd/dbdtmpl.html http://www.symbolstone.org/technology/perl/ DBI for DBI documentation http://www.symbolstone.org/technology/perl/ DBI http://lists.perl.org for DBI mailing list http://lists.perl.org

48 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 48 Where to Get More Information http://www.perl.com/pub/doc/manual/html/pod/perlg uts.html for information about Perl internal functions and how to exchange data between Perl and C. http://www.perl.com/pub/doc/manual/html/pod/perlg uts.html http://www.perl.com/pub/doc/manual/html/pod/perlx s.html for Perl XS reference manual http://www.perl.com/pub/doc/manual/html/pod/perlx s.html http://www.perl.org for Perl http://www.perl.org http://www.activestate.com for Win32 Perl http://www.activestate.com http://www.cpan.org for DBI and DBD modules http://www.cpan.org http://www.weihenstephan.de/~syring/win32/UnxUtil s.html for Win32 Unix utilities such as tar, bison and gzip etc. http://www.weihenstephan.de/~syring/win32/UnxUtil s.html

49 27/07/2001 Copyright 2001, Munica Corporation, www.munica.com 49 Thank You for Attending

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