Introduction to Perl - Day 2

1. Introduction to Perl Day 2 An Introduction to Perl Programming Dave Cross Magnum Solutions Ltd [email_address]

2. What We Will Cover Types of variable

3. Strict and warnings

4. References

5. Sorting

6. Reusable Code

7. Object Orientation

8. What We Will Cover Testing

9. Dates and Times

10. Templates

11. Databases

12. Further Information

13. Schedule 09:30 – Begin

14. 11:00 – Coffee break (30 mins)

15. 13:00 – Lunch (90 mins)

16. 14:30 – Begin

17. 16:00 – Coffee break (30 mins)

18. 18:00 – End

19. Resources Slides available on-line http://mag-sol.com/train/public/2009/yapc Also see Slideshare http://www.slideshare.net/davorg/slideshows Get Satisfaction http://getsatisfaction.com/magnum

20. Types of Variable

21. Types of Variable Perl variables are of two types

22. Important to know the difference

23. Lexical variables are created with my

24. Package variables are created by our

25. Lexical variables are associated with a code block

26. Package variables are associated with a package

27. Lexical Variables Created with my

28. my ($doctor, @timelords, %home_planets);

29. Live in a pad (associated with a block of code) Piece of code delimited by braces

30. Source file Only visible within enclosing block

31. "Lexical" because the scope is defined purely by the text

32. Packages All Perl code is associated with a package

33. A new package is created with package package MyPackage; Think of it as a namespace

34. Used to avoid name clashes with libraries

35. Default package is called main

36. Package Variables Live in a package's symbol table

37. Can be referred to using a fully qualified name $main::doctor

38. @Gallifrey::timelords Package name not required within own package

39. Can be seen from anywhere in the package (or anywhere at all when fully qualified)

40. Declaring Package Vars Can be predeclared with our

41. our ($doctor, @timelords, %home_planet);

42. Or (in older Perls) with use vars

43. use vars qw($doctor @timelords %home_planet);

44. Lexical or Package When to use lexical variables or package variables?

45. Simple answer Always use lexical variables More complete answer Always use lexical variables

46. Except for a tiny number of cases http://perl.plover.com/local.html

47. local You might see code that uses local

48. local $variable;

49. This doesn't do what you think it does

50. Badly named function

51. Doesn't create local variables

52. Creates a local copy of a package variable

53. Can be useful In a small number of cases

54. local Example $/ is a package variable

55. It defines the record separator

56. You might want to change it

57. Always localise changes

58. { local $/ = “\n\n”; while (<FILE> ) { ... } }

59. Strict and Warnings

60. Coding Safety Net Perl can be a very loose programming language

61. Two features can minimise the dangers

62. use strict / use warnings

63. A good habit to get into

64. No serious Perl programmer codes without them

65. use strict Controls three things

66. use strict 'refs' – no symbolic references

67. use strict 'subs' – no barewords

68. use strict 'vars' – no undeclared variables

69. use strict – turn on all three at once

70. turn them off (carefully) with no strict

71. use strict 'refs' Prevents symbolic references

72. aka "using a variable as another variable's name"

73. $what = 'dalek'; $$what = 'Karn'; # sets $dalek to 'Karn'

74. What if 'dalek' came from user input?

75. People often think this is a cool feature

76. It isn't

77. use strict 'refs' (cont) Better to use a hash

78. $what = 'dalek'; $alien{$what} = 'Karn';

79. Self contained namespace

80. Less chance of clashes

81. More information (e.g. all keys)

82. use strict 'subs' No barewords

83. Bareword is a word with no other interpretation

84. e.g. word without $, @, %, &

85. Treated as a function call or a quoted string

86. $dalek = Karn;

87. May clash with future reserved words

88. use strict 'vars' Forces predeclaration of variable names

89. Prevents typos

90. Less like BASIC - more like Ada

91. Thinking about scope is good

92. use warnings Warns against dubious programming habits

93. Some typical warnings Variables used only once

94. Using undefined variables

95. Writing to read-only file handles

96. And many more...

97. Allowing Warnings Sometimes it's too much work to make code warnings clean

98. Turn off use warnings locally

99. Turn off specific warnings

100. { no warnings 'deprecated'; # dodgy code ... }

101. See perldoc perllexwarn

102. References

103. Introducing References A reference is a bit like pointer in languages like C and Pascal (but better)

104. A reference is a unique way to refer to a variable.

105. A reference can always fit into a scalar variable

106. A reference looks like SCALAR(0x20026730)

107. Creating References Put \ in front of a variable name $scalar_ref = \$scalar;

108. $array_ref = \@array;

109. $hash_ref = \%hash; Can now treat it just like any other scalar $var = $scalar_ref;

110. $refs[0] = $array_ref;

111. $another_ref = $refs[0];

112. Creating References [ LIST ] creates anonymous array and returns a reference

113. $aref = [ 'this', 'is', 'a', 'list']; $aref2 = [ @array ];

114. { LIST } creates anonymous hash and returns a reference

115. $href = { 1 => 'one', 2 => 'two' }; $href = { %hash };

116. Creating References @arr = (1, 2, 3, 4); $aref1 = \@arr; $aref2 = [ @arr ]; print "$aref1\n$aref2\n";

117. Output ARRAY(0x20026800) ARRAY(0x2002bc00)

118. Second method creates a copy of the array

119. Using Array References Use {$aref} to get back an array that you have a reference to

120. Whole array

121. @array = @{$aref};

122. @rev = reverse @{$aref};

123. Single elements

124. $elem = ${$aref}[0];

125. ${$aref}[0] = 'foo';

126. Using Hash References Use {$href} to get back a hash that you have a reference to

127. Whole hash

128. %hash = %{$href};

129. @keys = keys %{$href};

130. Single elements

131. $elem = ${$href}{key};

132. ${$href}{key} = 'foo';

133. Using References Use arrow ( -> ) to access elements of arrays or hashes

134. Instead of ${$aref}[0] you can use $aref->[0]

135. Instead of ${$href}{key} you can use $href->{key}

136. Using References You can find out what a reference is referring to using ref

137. $aref = [ 1, 2, 3 ]; print ref $aref; # prints ARRAY

138. $href = { 1 => 'one', 2 => 'two' }; print ref $href; # prints HASH

139. Why Use References? Parameter passing

140. Complex data structures

141. Parameter Passing What does this do?

142. @arr1 = (1, 2, 3); @arr2 = (4, 5, 6); check_size(@arr1, @arr2); sub check_size { my (@a1, @a2) = @_; print @a1 == @a2 ? 'Yes' : 'No'; }

143. Why Doesn't It Work? my (@a1, @a2) = @_;

144. Arrays are combined in @_

145. All elements end up in @a1

146. How do we fix it?

147. Pass references to the arrays

148. Another Attempt @arr1 = (1, 2, 3); @arr2 = (4, 5, 6); check_size(\@arr1, \@arr2); sub check_size { my ($a1, $a2) = @_; print @$a1 == @$a2 ? 'Yes' : 'No'; }

149. Complex Data Structures Another good use for references

150. Try to create a 2-D array

151. @arr_2d = ((1, 2, 3), (4, 5, 6), (7, 8, 9));

152. @arr_2d contains (1, 2, 3, 4, 5, 6, 7, 8, 9)

153. This is known a array flattening

154. Complex Data Structures 2D Array using references

155. @arr_2d = ([1, 2, 3], [4, 5, 6], [7, 8, 9]);

156. But how do you access individual elements?

157. $arr_2d[1] is ref to array (4, 5, 6)

158. $arr_2d[1]->[1] is element 5

159. Complex Data Structures Another 2D Array

160. $arr_2d = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

161. $arr_2d->[1] is ref to array (4, 5, 6)

162. $arr_2d->[1]->[1] is element 5

163. Can omit intermediate arrows

164. $arr_2d->[1][1]

165. More Data Structures Imagine the following data file

166. Jones,Martha,UNIT Harkness,Jack,Torchwood Smith,Sarah Jane,Journalist

167. What would be a good data structure?

168. Hash for each record

169. Array of records

170. Array of hashes

171. More Data Structures Building an array of hashes

172. my @records; my @cols = ('s_name', 'f_name', 'job'); while (<FILE>) { chomp; my %rec; @rec{@cols} = split /,/; push @records, \%rec; }

173. Using an Array of Hashes foreach (@records) { print "$_->{f_name} ", "$_->{s_name} ". "is a $_->{job}\n"; }

174. Complex Data Structures Many more possibilities Hash of hashes

175. Hash of lists

176. Multiple levels (list of hash of hash, etc.) Lots of examples in “perldoc perldsc” (the data structures cookbook)

177. Sorting

178. Sorting Perl has a sort function that takes a list and sorts it

179. @sorted = sort @array;

180. Note that it does not sort the list in place

181. @array = sort @array;

182. Sort Order The default sort order is ASCII

183. @chars = sort 'e', 'b', 'a', 'd', 'c'; # @chars has ('a', 'b', 'c', 'd', 'e')

184. This can sometimes give strange results

185. @chars = sort 'E', 'b', 'a', 'D', 'c'; # @chars has ('D', 'E', 'a', 'b', 'c')

186. @nums = sort 1 .. 10; # @nums has (1, 10, 2, 3, 4, # 5, 6, 7, 8, 9)

187. Sorting Blocks Can add a "sorting block" to customise sort order

188. @nums = sort { $a <=> $b } 1 .. 10;

189. Perl puts two of the values from the list into $a and $b

190. Block compares values and returns -1, 0 or 1

191. <=> does this for numbers ( cmp for strings)

192. Sort Examples Other simple sort examples

193. sort { $b cmp $a } @words

194. sort { lc $a cmp lc $b } @words

195. sort { substr($a, 4) cmp substr($b, 4) } @lines

196. Sorting Subroutines Can also use a subroutine name in place of a code block

197. @words = sort dictionary @words; sub dictionary { # Don't change $a and $b my ($A, $B) = ($a, $b); $A =~ s/\W+//g; $B =~ s/\W+//g; $A cmp $B; }

198. Sorting Names my @names = ('Rose Tyler', 'Martha Jones', 'Donna Noble', 'Amy Pond'); @names = sort sort_names @names;

199. Need to write sort_names so that it sorts on surname and then forename.

200. Sorting Names (cont) sub sort_names { my @a = split /\s/, $a; my @b = split /\s/, $b; return $a[1] cmp $b[1] or $a[0] cmp $b[1]; }

201. More Complex Sorts sub sort_names { my @a = split /\s/, $a; my @b = split /\s/, $b; return $a[1] cmp $b[1] or $a[0] cmp $b[0]; }

202. Can be inefficient on large amounts of data

203. Multiple splits on the same data

204. More Efficient Sorts Split each row only once

205. @split = map { [ split ] } @names;

206. Do the comparison

207. @sort = sort { $a->[1] cmp $b->[1] or $a->[0] cmp $b->[0] } @split;

208. Join the data together

209. @names = map { join ' ', @$_ } @sort;

210. Put It All Together Can rewrite this as

211. @names = map { join ' ', @$_ } sort { $a->[1] cmp $b->[1] || $a->[0] cmp $b->[0] } map { [ split ] } @names;

212. All functions work on the output from the previous function in the chain

213. Schwartzian Transform @data_out = map { $_->[1] } sort { $a->[0] cmp $a->[0] } map { [func($_), $_] } @data_in;

214. Old Lisp trick

215. Named after Randal Schwartz

216. Reusable Code

217. Why Write Modules? Code reuse

218. Prevent reinventing the wheel

219. Easier to share across projects

220. Better design, more generic

221. Basic Module use strict; use warnings; package MyModule; use Exporter; our @ISA = ('Exporter'); our @EXPORT = ('my_sub'); sub my_sub { print "This is my_sub\n"; } 1;

222. Using MyModule.pm use MyModule; # my_sub is now available # for use within your # program my_sub(); # Prints "This is my_sub()"

223. Explaining MyModule.pm Much of MyModule.pm is concerned with exporting subroutine names

224. Subroutine full name MyModule::my_sub() Exporting abbreviates that my_sub()

225. Packages Revisited Every subroutine lives in a package

226. The default package is main

227. New packages are introduced with the package keyword

228. A subroutine's full name is package::name

229. Package name can be omitted from within same package

230. Like family names

231. Using Exporter The module Exporter.pm handles the export of subroutine (and variable) names

232. Exporter.pm defines a subroutine called import

233. import is automatically called whenever a module is used

234. import puts references to our subroutines into our caller's symbol table

235. How Exporter Works How does MyModule use Exporter's import subroutine?

236. We make use of inheritance

237. Inheritance is defined using the @ISA array

238. If we call a subroutine that doesn't exist in our module, then the modules in @ISA are also checked

239. Therefore Exporter::import is called

240. Exporting Symbols How does import know which subroutines to export?

241. Exports are defined in @EXPORT or @EXPORT_OK

242. Automatic exports are defined in @EXPORT

243. Optional exports are defined in @EXPORT_OK

244. Exporting Symbol Sets You can define sets of exports in %EXPORT_TAGS

245. Key is set name

246. Value is reference to an array of names

247. our %EXPORT_TAGS = (advanced => [ qw( my_sub my_other_sub ) ]; use MyModule qw(:advanced); my_sub(); my_other_sub();

248. Why Use @EXPORT_OK? Give your users the choice of which subroutines to import

249. Less chances of name clashes

250. Use @EXPORT_OK in preference to @EXPORT

251. Document the exported names and sets

252. Exporting Variables You can also export variables

253. @EXPORT_OK = qw($scalar, @array, %hash);

254. Can be part of export sets

255. Any variables you export must be package variables

256. Writing Modules The Easy Way A lot of module code is similar

257. Don't write the boilerplate yourself

258. Copy from an existing module

259. Or look at Module::Starter

260. Object Orientation

261. OO Programming Traditional programming has subroutines acting on methods

262. OO inverts this

263. Classes contain methods which define their actions

264. Objects are instances of classes

265. Perl has an OO system bolted on

266. Best of both worlds

267. Object Oriented Perl An Object is just a module that obeys certain extra rules

268. Three rules of Perl objects A Class is a package

269. An Object is a reference (usually to a hash)

270. A Method is a subroutine bless tells a reference what kind of object it is

271. A Simple Object package MyObject; sub new { my $class = shift; my $name = shift; my $self = { name => $name }; return bless $self, $class; }

272. A Simple Object (cont) sub get_name { my $self = shift; return $self->{name}; } sub set_name { my $self = shift; $self->{name} = shift; } 1;

273. Using MyObject.pm use MyObject; my $obj = MyObject->new('Dave'); print $obj->get_name; # prints 'Dave' $obj->set_name('David'); print $obj->get_name; # prints 'David'

274. Moose Easier OO Perl

275. Moose is on CPAN

276. Based on Perl 6 OO

277. Well worth investigating

278. Moose Example package MyModule; use Moose; has name => (is => 'rw', isa => 'Str', required => 1);

279. 1;

280. Further Information perldoc perlboot

281. perldoc perltoot

282. perldoc perlobj

283. perldoc perlbot

284. perldoc Moose (if it is installed)

285. Object Oriented Perl (Conway)

286. Testing

287. Testing Never program without a safety net

288. Does your code do what it is supposed to do?

289. Will your code continue to do what it is supposed to do?

290. Write unit tests

291. Run those tests all the time

292. When to Run Tests As often as possible

293. Before you add a feature

294. After you have added a feature

295. Before checking in code

296. Before releasing code

297. Constantly, automaticall y

298. Testing in Perl Perl makes it easy to write test suites

299. A lot of work in this area over the last eight years

300. Test::Simple and Test::More included in Perl distribution

301. Many more testing modules on CPAN

302. Simple Test Program use Test::More tests => 4; BEGIN { use_ok('My::Object'); } ok(my $obj = My::Object->new); isa_ok($obj, 'My::Object'); $obj->set_foo('Foo'); is($obj->get_foo, 'Foo');

303. Simple Test Output $ prove -v test.t test.... 1..4 ok 1 - use My::Object; ok 2 ok 3 - The object isa My::Object ok 4 ok All tests successful. Files=1, Tests=4, 0 wallclock secs ( 0.02 usr 0.00 sys + 0.05 cusr 0.00 csys = 0.07 CPU) Result: PASS

304. Adding Test Names use Test::More tests => 4; BEGIN { use_ok('My::Object'); } ok(my $obj = My::Object->new, 'Got an object'); isa_ok($obj, 'My::Object'); $obj->set_foo('Foo'); is($obj->get_foo, 'Foo', 'The foo is "Foo"');

305. Output With Names $ prove -v test2.t test2.... 1..4 ok 1 - use My::Object; ok 2 - got an object ok 3 - The object isa My::Object ok 4 - The foo is "Foo" ok All tests successful. Files=1, Tests=4, 0 wallclock secs ( 0.02 usr 0.00 sys + 0.05 cusr 0.00 csys = 0.07 CPU) Result: PASS

306. Using prove prove is a command line tool for running tests

307. Runs given tests using Test::Harness

308. Comes with the Perl distribution

309. Command line options -v verbose output

310. -r recurse

311. -s shuffle tests

312. Many more

313. Test Anything Protocol Perl tests have been spitting out “ok 1” and not “ok 2” for years

314. Now this ad-hoc format has a definition and a name

315. The Test Anything Protocol (TAP)

316. See Test::Harness::TAP (documentation module) and TAP::Parser

317. TAP Output More possibilities for test output TAP::Harness::Color

318. Test::TAP::HTMLMatrix Make sense of your test results

319. More Testing Modules Dozens of testing modules on CPAN

320. Some of my favourites

321. Test::File

322. Test::Exception, Test::Warn

323. Test::Differences

324. Test::XML (includes Test::XML::XPath)

325. Writing Test Modules These test modules all work together

326. Built using Test::Builder

327. Ensures that test modules all use the same framework

328. Use it as the basis of your own Test::* modules

329. Who tests the testers?

330. Test your Test::Builder test modules with Test::Builder::Tester

331. How Good Are Your Tests? How much of your code is exercised by your tests?

332. Devel::Cover can help you to find out

333. Deep internal magic

334. Draws pretty charts HARNESS_PERL_SWITCHES= -MDevel::Cover make test

335. cover

336. Devel::Cover Output

339. Alternative Test Paradigms Not everyone likes the Perl testing framework

340. Other frameworks are available

341. Test::Class xUnit style framework Test::FIT Framework for Interactive Testing

342. http://fit.c2.com

343. More Information Perl Testing: A Developer's Notebook (Ian Langworth & chromatic)

344. perldoc Test::Tutorial

345. perldoc Test::Simple

346. perldoc Test::More

347. perldoc Test::Builder

348. etc...

349. Dates and Times

350. Dates & Times Perl has built-in functions to handle dates and times

351. Flexible but confusing

352. time – seconds since 1st Jan 1970

353. localtime – convert to human-readable

354. timelocal (in Time::Local) – inverse of localtime

355. strftime (in POSIX) – formatting dates and times

356. Dates & Times on CPAN Look to CPAN for a better answer

357. Dozens of date/time modules on CPAN

358. Date::Manip is almost never what you want

359. Date::Calc, Date::Parse, Class::Date, Date::Simple, etc

360. Which one do you choose?

361. Perl DateTime Project http://datetime.perl.org/

362. "The DateTime family of modules present a unified way to handle dates and times in Perl"

363. "unified" is good

364. Dozens of modules that work together in a consistent fashion

365. Using DateTime use DateTime; my $dt = DateTime->now; say $dt; # 2009-08-02T15:06:07 say $dt->dmy, "\n"; # 2009-08-02 say $dt->hms, "\n"; # 15:06:07

366. Using DateTime use DateTime; my $dt = DateTime->new(year => 2009, month => 8, day => 2); say $dt->ymd('/'), "\n"; # 2009/08/02 say $dt->month; # 8 say $dt->month_name; # August

367. Arithmetic A DateTime object is a point in time

368. For date arithmetic you need a duration

369. Number of years, weeks, days, etc

370. Arithmetic use DateTime; my $dt = DateTime->new(year => 2009, month => 8, day => 2); my $two_weeks = DateTime::Duration->new(weeks => 2); $dt += $two_weeks; say $dt; # 2009-02-16T00:00:00

371. Formatting Output use DateTime; my $dt = DateTime->new(year => 2009, month => 2, day => 26); say $dt->strftime('%A, %d %B %Y'); # Tuesday, 26 February 2009

372. Control input format with DateTime::Format::Strptime

373. Parsing & Formatting Ready made parsers and formatters for popular date and time formats

374. DateTime::Format::HTTP

375. DateTime::Format::MySQL

376. DateTime::Format::Excel

377. DateTime::Format::Baby the big hand is on...

378. Alternative Calendars Handling non-standard calendars

379. DateTime::Calendar::Julian

380. DateTime::Calendar::Hebrew

381. DateTime::Calendar::Mayan

382. DateTime::Fiction::JRRTolkien::Shire

383. Calendar Examples use DateTime::Calendar::Mayan; my $dt = DateTime::Calendar::Mayan->now; say $dt->date; # 12.19.16.9.15

384. use DateTime::Fiction::JRRTolkien::Shire my $dt = DateTime::Fiction::JRRTolkien::Shire->now; say $dt->on_date; # Trewsday 1 Wedmath 7473

385. Templates

386. Templates Many people use templates to produce web pages

387. Advantages are well known

388. Standard look and feel (static/dynamic)

389. Reusable components

390. Separation of code logic from display logic

391. Different skill-sets (HTML vs Perl)

392. Non-Web Templates The same advantages apply to non-web areas

393. Reports

394. Business documents

395. Configuration files

396. Anywhere you produce output

397. DIY Templating Must be easy - so many people do it

398. See perlfaq4

399. “How can I expand variables in text strings?”

400. DIY Templating $text = 'this has a $foo in it and a $bar'; %user_defs = ( foo => 23, bar => 19, ); $text =~ s/\$(\w+)/$user_defs{$1}/g;

401. Don't do that

402. Templating Options Dozens of template modules on CPAN

403. Text::Template, HTML::Template, Mason, Template Toolkit

404. Many, many more

405. Questions to consider HTML only?

406. Template language I choose the Template Toolkit

407. Template Toolkit http://tt2.org/

408. Very powerful

409. Both web and non-web

410. Simple template language

411. Plugins give access to much of CPAN

412. Can use Perl code if you want But don't do that

413. Good Book Too!

414. The Template Equation Data + Template = Output

415. Data + Alternative Template = Alternative Output

416. Different views of the same data

417. Only the template changes

418. Simple TT Example use Template; use My::Object; my ($id, $format) = @ARGV; $format ||= 'html'; my $obj = My::Object->new($id) or die; my $tt = Template->new; $tt->process("$format.tt", { obj => $obj }, "$id.$format") or die $tt->error;

419. html.tt <html> <head> <title>[% obj.name %]</title> </head> <body> <h1>[% obj.name %]<h1> <p><img src=“[% obj.img %]” /><br /> [% obj.desc %]</p> <ul> [% FOREACH child IN obj.children -%] <li>[% child.name %]</li> [% END %] </body> </html>

420. text.tt [% obj.name | upper %] Image: [% obj.img %] [% obj.desc %] [% FOREACH child IN obj.children -%] * [% child.name %] [% END %]

421. Adding New Formats No new code required

422. Just add new output template

423. Perl programmer need not be involved

424. Equation Revisited Data + Template = Output Template Toolkit Template + Output = Data Template::Extract Data + Output = Template Template::Generate

425. Databases

426. Databases A large proportion of applications need to talk to databases

427. Perl has tools to make this as simple as possible

428. DBI is the basis for all modern Perl database access

429. You should be using DBI or something based on DBI

430. How DBI Works Program uses DBI.pm

431. Create a connection to a particular type of database

432. DBD module gets loaded

433. DBD translates from DBI API to database specific calls

434. DBD translates returned data into Perl data stuctures

435. Connecting to a DB use DBI; my $dbh = DBI->connect( "dbi:mysql:$some_stuff", $user, $pass );

436. “mysql” is the name of the DBD DBD::mysql In theory you can port a program to another database

437. Just change the connection line

438. Selecting Data Prepare the SQL statement

439. my $sth = $dbh->prepare( 'select name, genre from artist' );

440. my $sth = $dbh->prepare( "select title, from song where artist = '$id'");

441. Check return values (syntax errors)

442. Selecting Data (cont) Execute the statement

443. $sth->execute

444. Still need to check for errors

445. Selecting Data (cont) Fetch the returned data

446. while (my @row = $sth->fetchrow_array){ print "@row\n"; }

447. Fields are returned in the same order as they are defined in the query

448. Other Select Functions Other fetch methods are available: fetchrow_arrayref

449. fetchrow_hashref (keys are column names)

450. fetchall_arrayref

451. fetch (alias for fetchrow_arrayref) Many more added each week

452. Some Caveats If you're using a fetch method that returns an array Never use "select *"

453. For (hopefully) obvious reasons If you're using a fetch method that returns a hash Ensure all your columns have (unique) names

454. For (hopefully) obvious reasons

455. Insert, Update & Delete Statements that don't return data can be executed the same way

456. my $sql = "update table1 set col1 = '$val' where id_col = $id"; my $sth = $dbh->prepare($sql); $sth->execute;

457. But there's a shortcut

458. $rows = $dbh->do($sql);

459. Multiple Insertions while (<FILE>) { chomp; my @data = split; my $sql = "insert into tab values ($data[0], $data[1], $data[2]"); $dbh->do($sql); }

460. Recompiles the SQL every time

461. Very inefficient

462. Binding Data Prepare statement once, use many times

463. my $sql = "insert into tab values (?, ?, ?)"; my $sth = $dbh->prepare($sql); while (<FILE>) { my @data = split; bind_param(1, $data[0]); bind_param(2, $data[1]); bind_param(3, $data[2]); $sth->execute; }

464. Bonus - binding handles quoting for you

465. Binding Data (cont) Even easier – extra parameters to execute

466. my $sql = "insert into tab values (?, ?, ?)"; my $sth = $dbh->prepare($sql); while (<FILE>) { chomp; my @data = split; $sth->execute(@data); }

467. Unnamed Placeholders Having unnamed placeholders can get confusing

468. my $sql = 'insert into big_table values( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)';

469. Good chance of getting the variables in the wrong order

470. By the way - there's a basic maintainability error in that SQL

471. Bind By Name my $sql = 'insert into big_table (id, code, name, addr, email, url, ... ) values (:id, :code, :name, :addr, :email, :url, ... ); my $sth = $sql->prepare($sql); $sth->bind_param(':id', $id); $sth->bind_param(':code', $code); # etc $sth->execute;

472. Even Easier Binding Store your data in a hash

473. my %data = (id => 42, code => 'H2G2', ... ); # and later... foreach my $col (keys %data) { $sth->bind_param(":$col", $data{$col}; }

474. Downsides Many DBDs don't support it

475. Which is a bit of a bugger

476. Oracle does

477. So does PostgreSQL (tho' the docs discourage its use)

478. Check your DBD documentation

479. Email your friendly neighbourhood DBD author

480. Some Tips Make your life as easy as possible

481. Don't hard-code connection data Config file, command line options, environment variables Send all of your data access through one function

482. Store SQL queries externally and reference them by name

483. Use named bind parameters if you can

484. Sample Code my $dbh; sub run_sql { my ($sql_statement, %args) = @_; my $sql = get_sql($sql_statement); $dbh = get_dbh() unless $dbh; my $sth = $dbh->prepare($sql); foreach my $col (keys %args) { $sth->bind_param(":$col", $args{$col}); } return $sth->execute; }

485. Not Writing SQL Writing SQL is boring

486. It's often similar Select the id and name from this table

487. Select all the details of this row

488. Select something about related tables

489. Update this row with these values

490. Insert a new record with these values

491. Delete this record Must be a better way

492. Object Relational Mapping Mapping database relations into objects

493. Tables (relations) map onto classes

494. Rows (tuples) map onto objects

495. Columns (attributes) map onto attributes

496. Don't write SQL

497. Replacing SQL Instead of

498. SELECT * FROM my_table WHERE my_id = 10

499. and then dealing with the prepare/execute/fetch code

500. Replacing SQL We can write

501. use My::Object; # warning! not a real orm my $obj = My::Object->retrieve(10) $obj->name('A New Name'); $obj->save;

502. Or something similar

503. ORM on CPAN Very many ORMs on CPAN

504. Tangram

505. Alzabo

506. Class::DBI

507. DBIx::Class The current favourite

508. Highly recommended

509. Further Information perldoc DBI

510. perldoc DBD::* DBD::mysql

511. DBD::Oracle

512. Etc... perldoc DBIx::Class

513. Further Information

514. Perl Websites Perl Home Page http://www.perl.org CPAN http://www.cpan.org

515. http://search.cpan.org Perl Mongers (Perl User Groups)‏ http://www.pm.org

516. http://london.pm.org

517. Perl Websites use.perl – Perl News & Journals http://use.perl.org/ Perl Monks – Perl Help and Advice http://perlmonks.org/ Perl Documentation Online http://perldoc.perl.org/

518. Perl Conferences The Perl Conference (part of the Open Source Convention)‏ July 20-24 2009, San Jose, California

519. http://conferences.oreilly.com/oscon Yet Another Perl Conference August 3-5 2009, Lisbon, Portugal

520. http://www.yapceurope.org

521. Perl Conferences Other YAPCs Pittsburgh, Pennsylvania

522. Brazil

523. Tokyo OSDC Israel

524. Australia

525. Perl Workshops One-day grassroots conferences

526. UK, Germany, Israel, Pittsburgh, Nordic, Netherlands, France, Belgium, Russia, Minnesota, Austria

527. Perl Review Calendar www.theperlreview.com/community_calendar

528. Perl Mailing Lists See http://lists.perl.org for full details Perl Mongers (social discussion)‏

529. CGI

530. DBI

531. XML

532. Beginners

533. Advocacy

534. Fun with Perl

535. Perl Books Books for learning Perl Learning Perl (5th ed - June 2008) Schwartz, Phoenix & foy (O'Reilly)‏

536. Intermediate Perl Schwartz, foy & Phoenix (O'Reilly)‏

537. Beginning Perl Cozens (Wrox) http://www.perl.org/books/beginning-perl/

538. Perl Books Books you should have access to Programming Perl (3rd edition) Wall, Christiansen & Orwant (O'Reilly)‏

539. The Perl Cookbook (2nd edition) Christiansen & Torkington (O'Reilly)‏

540. Perl Best Practices Conway (O'Reilly)‏

541. Perl in a Nutshell Siever, Spainhour & Patwardhan (O'Reilly)‏

542. Perl Books Books you should probably look at Mastering Regular Expressions Friedl (O'Reilly)‏

543. Data Munging with Perl Cross (Manning)‏

544. Advanced Perl Programming Cozens (O'Reilly)‏

545. Perl Medic Scott (Addison Wesley)

546. Perl Books Specialised Perl books Object Oriented Perl Conway (Manning)‏

547. Programming the Perl DBI Descartes & Bunce (O'Reilly)‏

548. Writing CGI Applications with Perl Meltzer & Michelski (Addison Wesley)‏

549. Practical mod_perl Bekman & Cholet (O'Reilly)‏

550. Perl Template Toolkit Chamberlain, Cross & Wardley

551. Perl Magazines The Perl Review http://www.theperlreview.com

552. That's All Folks Any Questions?

Introduction to Perl - Day 2

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Introduction to Perl - Day 2