3 Catalyst::Manual::Tutorial::Debugging - Catalyst Tutorial Part 6: Debugging
9 This is B<Part 6 of 9> for the Catalyst tutorial.
11 L<Totorial Overview|Catalyst::Manual::Tutorial>
17 L<Introduction|Catalyst::Manual::Tutorial::Intro>
21 L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics>
25 L<Basic CRUD|Catalyst::Manual::Tutorial03_BasicCRUD>
29 L<Authentication|Catalyst::Manual::Tutorial::Authentication>
33 L<Authorization|Catalyst::Manual::Tutorial::Authorization>
41 L<Testing|Catalyst::Manual::Tutorial::Testing>
45 L<AdvancedCRUD|Catalyst::Manual::Tutorial::AdvancedCRUD>
49 L<Appendicies|Catalyst::Manual::Tutorial::Appendicies>
57 This part of the tutorial takes a brief look at the primary options available for troubleshooting Catalyst applications.
59 Note that when it comes to debugging and troubleshooting, there are two camps:
65 Fans of C<log> and C<print> statements embedded in the code.
69 Fans of interactive debuggers.
73 Catalyst is able to easily accommodate both styles of debugging.
79 Folks in the former group can use Catalyst's C<$c-E<gt>log> facility. For example, if you add the following code to a controller action method:
81 $c->log->debug("This is a test log message");
83 Then the Catalyst development server will display your message along with the other debug output. To accomplish the same thing in a TTSite view use:
85 [% Catalyst.log.debug("This is a test log message") %]
87 You can also use L<Data::Dumper|Data::Dumper> in both Catalyst code
88 (C<$c-E<gt>log-E<gt>dumper($myvar)>) and TT templates (C<[% Dumper.dump(book) %]> as discussed in earlier parts of the tutorial.
92 =head1 RUNNING CATALYST UNDER THE PERL DEBUGGER
94 Members of the interactive debuggers fan club will also be at home with Catalyst applications. One approach to this style of Perl debugging is to embed breakpoints in your code. For example, open C<lib/MyApp/Controller/Books.pm> in your editor and add the C<DB::single=1> line as follows inside the C<list> method (I like to "left-justify" my debug statements so I don't forget to remove them, but you can obviously indent them if you prefer):
97 # Retrieve the usual perl OO '$self' for this object. $c is the Catalyst
98 # 'Context' that's used to 'glue together' the various components
99 # that make up the application
104 # Retrieve all of the book records as book model objects and store in the
105 # stash where they can be accessed by the TT template
106 $c->stash->{books} = [$c->model('MyAppDB::Book')->all];
108 # Set the TT template to use. You will almost always want to do this
109 # in your action methods.
110 $c->stash->{template} = 'books/list.tt2';
113 This causes the Perl Debugger to enter "single step mode" when this command is
114 encountered (it has no effect when Perl is run without the C<-d> flag).
116 To now run the Catalyst development server under the Perl debugger, simply
117 prepend C<perl -d> to the front of C<script/myapp_server.pl>:
119 $ perl -d script/myapp_server.pl
121 This will start the interactive debugger and produce output similar to:
123 $ perl -d script/myapp_server.pl
125 Loading DB routines from perl5db.pl version 1.27
126 Editor support available.
128 Enter h or `h h' for help, or `man perldebug' for more help.
130 main::(script/myapp_server.pl:14): my $debug = 0;
134 Press the C<c> key and hit C<Enter> to continue executing the Catalyst development server under the debugger. Although execution speed will be slightly slower than normal, you should soon see the usual Catalyst startup debug information.
136 Now point your browser to L<http://localhost:3000/books/list> and log in. Once the breakpoint is encountered in the C<MyApp::Controller::list> method, the console session running the development server will drop to the Perl debugger prompt:
138 MyApp::Controller::Books::list(/home/me/MyApp/script/../lib/MyApp/Controller/Books.pm:40):
139 40: $c->stash->{books} = [$c->model('MyAppDB::Book')->all];
143 You now have the full Perl debugger at your disposal. First use the C<next> feature by typing C<n> to execute the C<all> method on the Book model (C<n> jumps over method/subroutine calls; you can also use C<s> to C<single-step> into methods/subroutines):
146 SELECT me.id, me.authors, me.title, me.rating FROM books me:
147 MyApp::Controller::Books::list(/home/me/MyApp/script/../lib/MyApp/Controller/Books.pm:44):
148 44: $c->stash->{template} = 'books/list.tt2';
152 This takes you to the next line of code where the template name is set. Notice that because we enabled C<DBIX_CLASS_STORAGE_DBI_DEBUG=1> earlier, SQL debug output also shows up in the development server debug output.
154 Next, list the methods available on our C<Book> model:
156 DB<1> m $c->model('MyAppDB::Book')
160 MODIFY_CODE_ATTRIBUTES
165 _result_class_accessor
166 _result_source_accessor
169 <lines removed for brevity>
173 We can also play with the model directly:
175 DB<2> x ($c->model('MyAppDB::Book')->all)[1]->title
176 SELECT me.id, me.title, me.rating FROM books me:
177 0 'TCP/IP Illustrated, Volume 1'
179 This uses the Perl debugger C<x> command to display the title of a book.
181 Next we inspect the C<books> element of the Catalyst C<stash> (the C<4> argument to the C<x> command limits the depth of the dump to 4 levels):
183 DB<3> x 4 $c->stash->{books}
185 0 MyApp::Model::MyAppDB::Book=HASH(0xb8e702c)
186 '_column_data' => HASH(0xb8e5e2c)
189 'title' => 'CCSP SNRS Exam Certification Guide'
191 <lines removed for brevity>
193 Then enter the C<c> command to continue processing until the next breakpoint is hit (or the application exits):
196 SELECT author.id, author.first_name, author.last_name FROM ...
198 Finally, press C<Ctrl+C> to break out of the development server. Because we are running inside the Perl debugger, you will drop to the debugger prompt. Press C<q> to exit the debugger and return to your OS shell prompt:
203 For more information on using the Perl debugger, please see C<perldebug> and C<perldebtut>. You can also type C<h> or C<h h> at the debugger prompt to view the built-in help screens.
209 Kennedy Clark, C<hkclark@gmail.com>
211 Please report any errors, issues or suggestions to the author.
213 Copyright 2006, Kennedy Clark. All rights reserved.
215 This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.