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1 | =head1 NAME |
2 | |
3 | Catalyst::Manual::Tutorial::Debugging - Catalyst Tutorial - Part 6: Debugging |
4 | |
5 | =head1 OVERVIEW |
6 | |
7 | This is B<Part 6 of 9> for the Catalyst tutorial. |
8 | |
9 | L<Tutorial Overview|Catalyst::Manual::Tutorial> |
10 | |
11 | =over 4 |
12 | |
13 | =item 1 |
14 | |
15 | L<Introduction|Catalyst::Manual::Tutorial::Intro> |
16 | |
17 | =item 2 |
18 | |
19 | L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics> |
20 | |
21 | =item 3 |
22 | |
23 | L<Basic CRUD|Catalyst::Manual::Tutorial_BasicCRUD> |
24 | |
25 | =item 4 |
26 | |
27 | L<Authentication|Catalyst::Manual::Tutorial::Authentication> |
28 | |
29 | =item 5 |
30 | |
31 | L<Authorization|Catalyst::Manual::Tutorial::Authorization> |
32 | |
33 | =item 6 |
34 | |
35 | B<Debugging> |
36 | |
37 | =item 7 |
38 | |
39 | L<Testing|Catalyst::Manual::Tutorial::Testing> |
40 | |
41 | =item 8 |
42 | |
43 | L<AdvancedCRUD|Catalyst::Manual::Tutorial::AdvancedCRUD> |
44 | |
45 | =item 9 |
46 | |
47 | L<Appendices|Catalyst::Manual::Tutorial::Appendices> |
48 | |
49 | =back |
50 | |
51 | |
52 | =head1 DESCRIPTION |
53 | |
54 | This part of the tutorial takes a brief look at the primary options |
55 | available for troubleshooting Catalyst applications. |
56 | |
57 | Note that when it comes to debugging and troubleshooting, there are two |
58 | camps: |
59 | |
60 | =over 4 |
61 | |
62 | =item * |
63 | |
64 | Fans of C<log> and C<print> statements embedded in the code. |
65 | |
66 | =item * |
67 | |
68 | Fans of interactive debuggers. |
69 | |
70 | =back |
71 | |
72 | Catalyst is able to easily accommodate both styles of debugging. |
73 | |
74 | =head1 LOG STATEMENTS |
75 | |
76 | Folks in the former group can use Catalyst's C<$c-E<gt>log> facility. |
77 | (See L<Catalyst::Log> for more detail.) For example, if you add the |
78 | following code to a controller action method: |
79 | |
80 | $c->log->info("Starting the foreach loop here"); |
81 | |
82 | $c->log->debug("Value of $id is: ".$id); |
83 | |
84 | Then the Catalyst development server will display your message along |
85 | with the other debug output. To accomplish the same thing in a TTSite |
86 | view use: |
87 | |
88 | [% Catalyst.log.debug("This is a test log message") %] |
89 | |
90 | You can also use L<Data::Dumper|Data::Dumper> in both Catalyst code |
91 | (C<use Data::Dumper; $c-E<gt>log-E<gt>debug("$var is: ".Dumper($var));)>) |
92 | and TT templates (C<[% Dumper.dump(book) %]>. |
93 | |
94 | =head1 RUNNING CATALYST UNDER THE PERL DEBUGGER |
95 | |
96 | Members of the interactive-debugger fan club will also be at home with |
97 | Catalyst applications. One approach to this style of Perl debugging is |
98 | to embed breakpoints in your code. For example, open |
99 | C<lib/MyApp/Controller/Books.pm> in your editor and add the |
100 | C<DB::single=1> line as follows inside the C<list> method (I like to |
101 | "left-justify" my debug statements so I don't forget to remove them, but |
102 | you can obviously indent them if you prefer): |
103 | |
104 | sub list : Local { |
105 | # Retrieve the usual perl OO '$self' for this object. $c is the Catalyst |
106 | # 'Context' that's used to 'glue together' the various components |
107 | # that make up the application |
108 | my ($self, $c) = @_; |
109 | |
110 | $DB::single=1; |
111 | |
112 | # Retrieve all of the book records as book model objects and store in the |
113 | # stash where they can be accessed by the TT template |
114 | $c->stash->{books} = [$c->model('MyAppDB::Book')->all]; |
115 | |
116 | # Set the TT template to use. You will almost always want to do this |
117 | # in your action methods. |
118 | $c->stash->{template} = 'books/list.tt2'; |
119 | } |
120 | |
121 | This causes the Perl Debugger to enter "single step mode" when this command is |
122 | encountered (it has no effect when Perl is run without the C<-d> flag). |
123 | |
124 | To now run the Catalyst development server under the Perl debugger, simply |
125 | prepend C<perl -d> to the front of C<script/myapp_server.pl>: |
126 | |
127 | $ perl -d script/myapp_server.pl |
128 | |
129 | This will start the interactive debugger and produce output similar to: |
130 | |
131 | $ perl -d script/myapp_server.pl |
132 | |
133 | Loading DB routines from perl5db.pl version 1.27 |
134 | Editor support available. |
135 | |
136 | Enter h or `h h' for help, or `man perldebug' for more help. |
137 | |
138 | main::(script/myapp_server.pl:14): my $debug = 0; |
139 | |
140 | DB<1> |
141 | |
142 | Press the C<c> key and hit C<Enter> to continue executing the Catalyst |
143 | development server under the debugger. Although execution speed will be |
144 | slightly slower than normal, you should soon see the usual Catalyst |
145 | startup debug information. |
146 | |
147 | Now point your browser to L<http://localhost:3000/books/list> and log |
148 | in. Once the breakpoint is encountered in the |
149 | C<MyApp::Controller::list> method, the console session running the |
150 | development server will drop to the Perl debugger prompt: |
151 | |
152 | MyApp::Controller::Books::list(/home/me/MyApp/script/../lib/MyApp/Controller/Books.pm:40): |
153 | 40: $c->stash->{books} = [$c->model('MyAppDB::Book')->all]; |
154 | |
155 | DB<1> |
156 | |
157 | You now have the full Perl debugger at your disposal. First use the |
158 | C<next> feature by typing C<n> to execute the C<all> method on the Book |
159 | model (C<n> jumps over method/subroutine calls; you can also use C<s> to |
160 | C<single-step> into methods/subroutines): |
161 | |
162 | DB<1> n |
163 | SELECT me.id, me.authors, me.title, me.rating FROM books me: |
164 | MyApp::Controller::Books::list(/home/me/MyApp/script/../lib/MyApp/Controller/Books.pm:44): |
165 | 44: $c->stash->{template} = 'books/list.tt2'; |
166 | |
167 | DB<1> |
168 | |
169 | This takes you to the next line of code where the template name is set. |
170 | Notice that because we enabled C<DBIC_TRACE=1> earlier, SQL debug |
171 | output also shows up in the development server debug information. |
172 | |
173 | Next, list the methods available on our C<Book> model: |
174 | |
175 | DB<1> m $c->model('MyAppDB::Book') |
176 | () |
177 | (0+ |
178 | (bool |
179 | MODIFY_CODE_ATTRIBUTES |
180 | _attr_cache |
181 | _collapse_result |
182 | _construct_object |
183 | _count |
184 | _result_class_accessor |
185 | _result_source_accessor |
186 | all |
187 | carp |
188 | <lines removed for brevity> |
189 | |
190 | DB<2> |
191 | |
192 | We can also play with the model directly: |
193 | |
194 | DB<2> x ($c->model('MyAppDB::Book')->all)[1]->title |
195 | SELECT me.id, me.title, me.rating FROM books me: |
196 | 0 'TCP/IP Illustrated, Volume 1' |
197 | |
198 | This uses the Perl debugger C<x> command to display the title of a book. |
199 | |
200 | Next we inspect the C<books> element of the Catalyst C<stash> (the C<4> |
201 | argument to the C<x> command limits the depth of the dump to 4 levels): |
202 | |
203 | DB<3> x 4 $c->stash->{books} |
204 | 0 ARRAY(0xa8f3b7c) |
205 | 0 MyApp::Model::MyAppDB::Book=HASH(0xb8e702c) |
206 | '_column_data' => HASH(0xb8e5e2c) |
207 | 'id' => 1 |
208 | 'rating' => 5 |
209 | 'title' => 'CCSP SNRS Exam Certification Guide' |
210 | '_in_storage' => 1 |
211 | <lines removed for brevity> |
212 | |
213 | Then enter the C<c> command to continue processing until the next |
214 | breakpoint is hit (or the application exits): |
215 | |
216 | DB<4> c |
217 | SELECT author.id, author.first_name, author.last_name FROM ... |
218 | |
219 | Finally, press C<Ctrl+C> to break out of the development server. |
220 | Because we are running inside the Perl debugger, you will drop to the |
221 | debugger prompt. Press C<q> to exit the debugger and return to your OS |
222 | shell prompt: |
223 | |
224 | DB<4> q |
225 | $ |
226 | |
227 | For more information on using the Perl debugger, please see C<perldebug> |
228 | and C<perldebtut>. You can also type C<h> or C<h h> at the debugger |
229 | prompt to view the built-in help screens. |
230 | |
231 | |
232 | =head1 DEBUGGING MODULES FROM CPAN |
233 | |
234 | Although the techniques discussed above work well for code you are |
235 | writing, what if you want to use print/log/warn messages or set |
236 | breakpoints in code that you have installed from CPAN (or in module that |
237 | ship with Perl)? One helpful approach is to place a copy of the module |
238 | inside the C<lib> directory of your Catalyst project. When Catalyst |
239 | loads, it will load from inside your C<lib> directory first, only |
240 | turning to the global modules if a local copy cannot be found. You can |
241 | then make modifications such as adding a C<$DB::single=1> to the local |
242 | copy of the module without risking the copy in the original location. |
243 | This can also be a great way to "locally override" bugs in modules while |
244 | you wait for a fix on CPAN. |
245 | |
246 | |
247 | Matt Trout has suggested the following shortcut to create a local |
248 | copy of an installed module: |
249 | |
250 | mkdir -p lib/Module; cp `perldoc -l Module::Name` lib/Module/ |
251 | |
252 | For example, you could make a copy of |
253 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> |
254 | with the following command: |
255 | |
256 | mkdir -p lib/Catalyst/Plugin; cp \ |
257 | `perldoc -l Catalyst::Plugin::Authentication` lib/Catalyst/Plugin |
258 | |
259 | B<Note:> Matt has also suggested the following tips for Perl |
260 | debugging: |
261 | |
262 | =over 4 |
263 | |
264 | =item * |
265 | |
266 | Check the version of an installed module: |
267 | |
268 | perl -MModule::Name -e 'print $Module::Name::VERSION;' |
269 | |
270 | For example: |
271 | |
272 | $ perl -MCatalyst::Plugin::Authentication -e \ |
273 | 'print $Catalyst::Plugin::Authentication::VERSION;' |
274 | 0.07 |
275 | |
276 | =item * |
277 | |
278 | Check if a modules contains a given method: |
279 | |
280 | perl -MModule::Name -e 'print Module::Name->can("method");' |
281 | |
282 | For example: |
283 | |
284 | $ perl -MCatalyst::Plugin::Authentication -e \ |
285 | 'print Catalyst::Plugin::Authentication->can("prepare");' |
286 | CODE(0x9c8db2c) |
287 | |
288 | If the method exists, the Perl C<can> method returns a coderef. |
289 | Otherwise, it returns undef and nothing will be printed. |
290 | |
291 | =back |
292 | |
293 | |
294 | =head1 AUTHOR |
295 | |
296 | Kennedy Clark, C<hkclark@gmail.com> |
297 | |
298 | Please report any errors, issues or suggestions to the author. The |
299 | most recent version of the Catalyst Tutorial can be found at |
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300 | L<http://dev.catalyst.perl.org/repos/Catalyst/trunk/Catalyst-Manual/lib/Catalyst/Manual/Tutorial/>. |
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301 | |
302 | Copyright 2006, Kennedy Clark, under Creative Commons License |
303 | (L<http://creativecommons.org/licenses/by-nc-sa/2.5/>). |