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1 | =head1 NAME |
2 | |
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3 | Catalyst::Manual::Tutorial::Debugging - Catalyst Tutorial - Chapter 7: Debugging |
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4 | |
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5 | |
6 | =head1 OVERVIEW |
7 | |
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8 | This is B<Chapter 7 of 10> for the Catalyst tutorial. |
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9 | |
10 | L<Tutorial Overview|Catalyst::Manual::Tutorial> |
11 | |
12 | =over 4 |
13 | |
14 | =item 1 |
15 | |
16 | L<Introduction|Catalyst::Manual::Tutorial::Intro> |
17 | |
18 | =item 2 |
19 | |
20 | L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics> |
21 | |
22 | =item 3 |
23 | |
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24 | L<More Catalyst Basics|Catalyst::Manual::Tutorial::MoreCatalystBasics> |
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25 | |
26 | =item 4 |
27 | |
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28 | L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD> |
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29 | |
30 | =item 5 |
31 | |
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32 | L<Authentication|Catalyst::Manual::Tutorial::Authentication> |
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33 | |
34 | =item 6 |
35 | |
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36 | L<Authorization|Catalyst::Manual::Tutorial::Authorization> |
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37 | |
38 | =item 7 |
39 | |
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40 | B<Debugging> |
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41 | |
42 | =item 8 |
43 | |
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44 | L<Testing|Catalyst::Manual::Tutorial::Testing> |
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45 | |
46 | =item 9 |
47 | |
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48 | L<Advanced CRUD|Catalyst::Manual::Tutorial::AdvancedCRUD> |
49 | |
50 | =item 10 |
51 | |
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52 | L<Appendices|Catalyst::Manual::Tutorial::Appendices> |
53 | |
54 | =back |
55 | |
56 | |
57 | =head1 DESCRIPTION |
58 | |
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59 | This chapter of the tutorial takes a brief look at the primary options |
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60 | available for troubleshooting Catalyst applications. |
61 | |
62 | Note that when it comes to debugging and troubleshooting, there are two |
63 | camps: |
64 | |
65 | =over 4 |
66 | |
67 | =item * |
68 | |
69 | Fans of C<log> and C<print> statements embedded in the code. |
70 | |
71 | =item * |
72 | |
73 | Fans of interactive debuggers. |
74 | |
75 | =back |
76 | |
77 | Catalyst is able to easily accommodate both styles of debugging. |
78 | |
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79 | |
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80 | =head1 LOG STATEMENTS |
81 | |
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82 | Folks in the former group can use Catalyst's C<$c-E<gt>log> facility. |
83 | (See L<Catalyst::Log|Catalyst::Log> for more detail.) For example, if |
84 | you add the following code to a controller action method: |
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85 | |
86 | $c->log->info("Starting the foreach loop here"); |
87 | |
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88 | $c->log->debug("Value of \$id is: ".$id); |
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89 | |
90 | Then the Catalyst development server will display your message along |
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91 | with the other debug output. To accomplish the same thing in a TT |
92 | template view use: |
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93 | |
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94 | [% c.log.debug("This is a test log message") %] |
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95 | |
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96 | As with many other logging facilities, you a method is defined for |
97 | each of the following "logging levels" (in increasing order of |
98 | severity/importance): |
99 | |
100 | $c->log->debug |
101 | $c->log->info |
102 | $c->log->warn |
103 | $c->log->error |
104 | $c->log->fatal |
105 | |
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106 | You can also use L<Data::Dumper|Data::Dumper> in both Catalyst code |
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107 | (C<use Data::Dumper; $c-E<gt>log-E<gt>debug("\$var is: ".Dumper($var));)>) |
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108 | and TT templates (C<[% Dumper.dump(book) %]>. |
109 | |
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110 | |
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111 | =head1 RUNNING CATALYST UNDER THE PERL DEBUGGER |
112 | |
113 | Members of the interactive-debugger fan club will also be at home with |
114 | Catalyst applications. One approach to this style of Perl debugging is |
115 | to embed breakpoints in your code. For example, open |
116 | C<lib/MyApp/Controller/Books.pm> in your editor and add the |
117 | C<DB::single=1> line as follows inside the C<list> method (I like to |
118 | "left-justify" my debug statements so I don't forget to remove them, but |
119 | you can obviously indent them if you prefer): |
120 | |
121 | sub list : Local { |
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122 | # Retrieve the usual Perl OO '$self' for this object. $c is the Catalyst |
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123 | # 'Context' that's used to 'glue together' the various components |
124 | # that make up the application |
125 | my ($self, $c) = @_; |
126 | |
127 | $DB::single=1; |
128 | |
129 | # Retrieve all of the book records as book model objects and store in the |
130 | # stash where they can be accessed by the TT template |
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131 | $c->stash->{books} = [$c->model('DB::Books')->all]; |
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132 | |
133 | # Set the TT template to use. You will almost always want to do this |
134 | # in your action methods. |
135 | $c->stash->{template} = 'books/list.tt2'; |
136 | } |
137 | |
138 | This causes the Perl Debugger to enter "single step mode" when this command is |
139 | encountered (it has no effect when Perl is run without the C<-d> flag). |
140 | |
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141 | B<NOTE:> The C<DB> here is the Perl Debugger, not the DB model. |
142 | |
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143 | To now run the Catalyst development server under the Perl debugger, simply |
144 | prepend C<perl -d> to the front of C<script/myapp_server.pl>: |
145 | |
146 | $ perl -d script/myapp_server.pl |
147 | |
148 | This will start the interactive debugger and produce output similar to: |
149 | |
150 | $ perl -d script/myapp_server.pl |
151 | |
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152 | Loading DB routines from perl5db.pl version 1.3 |
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153 | Editor support available. |
154 | |
155 | Enter h or `h h' for help, or `man perldebug' for more help. |
156 | |
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157 | main::(script/myapp_server.pl:16): my $debug = 0; |
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158 | |
159 | DB<1> |
160 | |
161 | Press the C<c> key and hit C<Enter> to continue executing the Catalyst |
162 | development server under the debugger. Although execution speed will be |
163 | slightly slower than normal, you should soon see the usual Catalyst |
164 | startup debug information. |
165 | |
166 | Now point your browser to L<http://localhost:3000/books/list> and log |
167 | in. Once the breakpoint is encountered in the |
168 | C<MyApp::Controller::list> method, the console session running the |
169 | development server will drop to the Perl debugger prompt: |
170 | |
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171 | MyApp::Controller::Books::list(/home/me/MyApp/script/../lib/MyApp/Controller/Books.pm:48): |
172 | 48: $c->stash->{books} = [$c->model('DB::Books')->all]; |
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173 | |
174 | DB<1> |
175 | |
176 | You now have the full Perl debugger at your disposal. First use the |
177 | C<next> feature by typing C<n> to execute the C<all> method on the Book |
178 | model (C<n> jumps over method/subroutine calls; you can also use C<s> to |
179 | C<single-step> into methods/subroutines): |
180 | |
181 | DB<1> n |
182 | SELECT me.id, me.authors, me.title, me.rating FROM books me: |
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183 | MyApp::Controller::Books::list(/home/me/MyApp/script/../lib/MyApp/Controller/Books.pm:53): |
184 | 53: $c->stash->{template} = 'books/list.tt2'; |
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185 | |
186 | DB<1> |
187 | |
188 | This takes you to the next line of code where the template name is set. |
189 | Notice that because we enabled C<DBIC_TRACE=1> earlier, SQL debug |
190 | output also shows up in the development server debug information. |
191 | |
192 | Next, list the methods available on our C<Book> model: |
193 | |
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194 | DB<1> m $c->model('DB::Books') |
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195 | () |
196 | (0+ |
197 | (bool |
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198 | __source_handle_accessor |
199 | _add_alias |
200 | _build_unique_query |
201 | _calculate_score |
202 | _collapse_cond |
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203 | <lines removed for brevity> |
204 | |
205 | DB<2> |
206 | |
207 | We can also play with the model directly: |
208 | |
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209 | DB<2> x ($c->model('DB::Books')->all)[1]->title |
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210 | SELECT me.id, me.title, me.rating FROM books me: |
211 | 0 'TCP/IP Illustrated, Volume 1' |
212 | |
213 | This uses the Perl debugger C<x> command to display the title of a book. |
214 | |
215 | Next we inspect the C<books> element of the Catalyst C<stash> (the C<4> |
216 | argument to the C<x> command limits the depth of the dump to 4 levels): |
217 | |
218 | DB<3> x 4 $c->stash->{books} |
219 | 0 ARRAY(0xa8f3b7c) |
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220 | 0 MyApp::Model::DB::Book=HASH(0xb8e702c) |
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221 | '_column_data' => HASH(0xb8e5e2c) |
222 | 'id' => 1 |
223 | 'rating' => 5 |
224 | 'title' => 'CCSP SNRS Exam Certification Guide' |
225 | '_in_storage' => 1 |
226 | <lines removed for brevity> |
227 | |
228 | Then enter the C<c> command to continue processing until the next |
229 | breakpoint is hit (or the application exits): |
230 | |
231 | DB<4> c |
232 | SELECT author.id, author.first_name, author.last_name FROM ... |
233 | |
234 | Finally, press C<Ctrl+C> to break out of the development server. |
235 | Because we are running inside the Perl debugger, you will drop to the |
236 | debugger prompt. Press C<q> to exit the debugger and return to your OS |
237 | shell prompt: |
238 | |
239 | DB<4> q |
240 | $ |
241 | |
242 | For more information on using the Perl debugger, please see C<perldebug> |
243 | and C<perldebtut>. You can also type C<h> or C<h h> at the debugger |
244 | prompt to view the built-in help screens. |
245 | |
246 | |
247 | =head1 DEBUGGING MODULES FROM CPAN |
248 | |
249 | Although the techniques discussed above work well for code you are |
250 | writing, what if you want to use print/log/warn messages or set |
251 | breakpoints in code that you have installed from CPAN (or in module that |
252 | ship with Perl)? One helpful approach is to place a copy of the module |
253 | inside the C<lib> directory of your Catalyst project. When Catalyst |
254 | loads, it will load from inside your C<lib> directory first, only |
255 | turning to the global modules if a local copy cannot be found. You can |
256 | then make modifications such as adding a C<$DB::single=1> to the local |
257 | copy of the module without risking the copy in the original location. |
258 | This can also be a great way to "locally override" bugs in modules while |
259 | you wait for a fix on CPAN. |
260 | |
261 | |
262 | Matt Trout has suggested the following shortcut to create a local |
263 | copy of an installed module: |
264 | |
265 | mkdir -p lib/Module; cp `perldoc -l Module::Name` lib/Module/ |
266 | |
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267 | Note: If you are following along in Debian 5, you will need to install |
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268 | the C<perl-doc> package to use the C<perldoc> command. Use |
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269 | C<sudo aptitude install perl-doc> to do that. |
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270 | |
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271 | For example, you could make a copy of |
272 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> |
273 | with the following command: |
274 | |
275 | mkdir -p lib/Catalyst/Plugin; cp \ |
276 | `perldoc -l Catalyst::Plugin::Authentication` lib/Catalyst/Plugin |
277 | |
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278 | You can then use the local copy inside your project to place logging |
279 | messages and/or breakpoints for further study of that module. |
280 | |
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281 | B<Note:> Matt has also suggested the following tips for Perl |
282 | debugging: |
283 | |
284 | =over 4 |
285 | |
286 | =item * |
287 | |
288 | Check the version of an installed module: |
289 | |
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290 | perl -ME<lt>mod_nameE<gt> -e '"print $E<lt>mod_nameE<gt>::VERSION\n"' |
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291 | |
292 | For example: |
293 | |
294 | $ perl -MCatalyst::Plugin::Authentication -e \ |
295 | 'print $Catalyst::Plugin::Authentication::VERSION;' |
296 | 0.07 |
297 | |
298 | =item * |
299 | |
300 | Check if a modules contains a given method: |
301 | |
302 | perl -MModule::Name -e 'print Module::Name->can("method");' |
303 | |
304 | For example: |
305 | |
306 | $ perl -MCatalyst::Plugin::Authentication -e \ |
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307 | 'print Catalyst::Plugin::Authentication->can("user");' |
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308 | CODE(0x9c8db2c) |
309 | |
310 | If the method exists, the Perl C<can> method returns a coderef. |
311 | Otherwise, it returns undef and nothing will be printed. |
312 | |
313 | =back |
314 | |
315 | |
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316 | =head1 TT DEBUGGING |
317 | |
318 | If you run into issues during the rendering of your template, it might |
319 | be helpful to enable TT C<DEBUG> options. You can do this in a Catalyst |
320 | environment by adding a C<DEBUG> line to the C<__PACKAGE__->config> |
321 | declaration in C<lib/MyApp/View/TT.pm>: |
322 | |
323 | __PACKAGE__->config({ |
324 | TEMPLATE_EXTENSION => '.tt2', |
325 | DEBUG => 'undef', |
326 | }); |
327 | |
328 | There are a variety of options you can use, such as 'undef', 'all', |
329 | 'service', 'context', 'parser' and 'provider'. See |
330 | L<Template::Constants|Template::Constants> for more information |
331 | (remove the C<DEBUG_> portion of the name shown in the TT docs and |
332 | convert to lower case for use inside Catalyst). |
333 | |
334 | B<NOTE:> B<Please be sure to disable TT debug options before continuing |
335 | with the tutorial> (especially the 'undef' option -- leaving this |
336 | enabled will conflict with several of the conventions used by this |
337 | tutorial to leave some variables undefined on purpose). |
338 | |
339 | |
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340 | =head1 AUTHOR |
341 | |
342 | Kennedy Clark, C<hkclark@gmail.com> |
343 | |
344 | Please report any errors, issues or suggestions to the author. The |
345 | most recent version of the Catalyst Tutorial can be found at |
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346 | L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.70/trunk/lib/Catalyst/Manual/Tutorial/>. |
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347 | |
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348 | Copyright 2006-2008, Kennedy Clark, under Creative Commons License |
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349 | (L<http://creativecommons.org/licenses/by-sa/3.0/us/>). |