3 Catalyst::Manual::Tutorial::Authentication - Catalyst Tutorial - Part 5: Authentication
8 This is B<Part 5 of 10> for the Catalyst tutorial.
10 L<Tutorial Overview|Catalyst::Manual::Tutorial>
16 L<Introduction|Catalyst::Manual::Tutorial::Intro>
20 L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics>
24 L<More Catalyst Basics|Catalyst::Manual::Tutorial::MoreCatalystBasics>
28 L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD>
36 L<Authorization|Catalyst::Manual::Tutorial::Authorization>
40 L<Debugging|Catalyst::Manual::Tutorial::Debugging>
44 L<Testing|Catalyst::Manual::Tutorial::Testing>
48 L<Advanced CRUD|Catalyst::Manual::Tutorial::AdvancedCRUD>
52 L<Appendices|Catalyst::Manual::Tutorial::Appendices>
59 Now that we finally have a simple yet functional application, we can
60 focus on providing authentication (with authorization coming next in
63 This part of the tutorial is divided into two main sections: 1) basic,
64 cleartext authentication and 2) hash-based authentication.
66 You can checkout the source code for this example from the catalyst
67 subversion repository as per the instructions in
68 L<Catalyst::Manual::Tutorial::Intro>
70 =head1 BASIC AUTHENTICATION
72 This section explores how to add authentication logic to a Catalyst
76 =head2 Add Users and Roles to the Database
78 First, we add both user and role information to the database (we will
79 add the role information here although it will not be used until the
80 authorization section, Part 5). Create a new SQL script file by opening
81 C<myapp02.sql> in your editor and insert:
84 -- Add users and roles tables, along with a many-to-many join table
87 id INTEGER PRIMARY KEY,
96 id INTEGER PRIMARY KEY,
99 CREATE TABLE user_roles (
102 PRIMARY KEY (user_id, role_id)
105 -- Load up some initial test data
107 INSERT INTO users VALUES (1, 'test01', 'mypass', 't01@na.com', 'Joe', 'Blow', 1);
108 INSERT INTO users VALUES (2, 'test02', 'mypass', 't02@na.com', 'Jane', 'Doe', 1);
109 INSERT INTO users VALUES (3, 'test03', 'mypass', 't03@na.com', 'No', 'Go', 0);
110 INSERT INTO roles VALUES (1, 'user');
111 INSERT INTO roles VALUES (2, 'admin');
112 INSERT INTO user_roles VALUES (1, 1);
113 INSERT INTO user_roles VALUES (1, 2);
114 INSERT INTO user_roles VALUES (2, 1);
115 INSERT INTO user_roles VALUES (3, 1);
117 Then load this into the C<myapp.db> database with the following command:
119 $ sqlite3 myapp.db < myapp02.sql
122 =head2 Add User and Role Information to DBIC Schema
124 Although we could manually edit the DBIC schema information to include
125 the new tables added in the previous step, let's use the C<create=static>
126 option on the DBIC model helper to do most of the work for us:
128 $ script/myapp_create.pl model MyAppDB DBIC::Schema MyApp::Schema::MyAppDB create=static dbi:SQLite:myapp.db
129 $ ls lib/MyApp/Schema/MyAppDB
130 Authors.pm BookAuthors.pm Books.pm Roles.pm UserRoles.pm Users.pm
132 Notice how the helper has added three new table-specific result source
133 files to the C<lib/MyApp/Schema/MyApp> directory. And, more
134 importantly, even if there were changes to the existing result source
135 files, those changes would have only been written above the C<# DO NOT
136 MODIFY THIS OR ANYTHING ABOVE!> comment and your hand-editted
137 enhancements would have been preserved.
140 Speaking of "hand-editted enhancements," we should now add
141 relationship information to the three new result source files. Edit
142 each of these files and add the following information between the C<#
143 DO NOT MODIFY THIS OR ANYTHING ABOVE!> comment and the closing C<1;>:
145 C<lib/MyApp/Schema/MyAppDB/Users.pm>:
153 # 1) Name of relationship, DBIC will create accessor with this name
154 # 2) Name of the model class referenced by this relationship
155 # 3) Column name in *foreign* table
156 __PACKAGE__->has_many(map_user_role => 'MyApp::Schema::MyAppDB::UserRoles', 'user_id');
160 # 1) Name of relationship, DBIC will create accessor with this name
161 # 2) Name of has_many() relationship this many_to_many() is shortcut for
162 # 3) Name of belongs_to() relationship in model class of has_many() above
163 # You must already have the has_many() defined to use a many_to_many().
164 __PACKAGE__->many_to_many(roles => 'map_user_role', 'role');
167 C<lib/MyApp/Schema/MyAppDB/Roles.pm>:
175 # 1) Name of relationship, DBIC will create accessor with this name
176 # 2) Name of the model class referenced by this relationship
177 # 3) Column name in *foreign* table
178 __PACKAGE__->has_many(map_user_role => 'MyApp::Schema::MyAppDB::UserRoles', 'role_id');
181 C<lib/MyApp/Schema/MyAppDB/UserRoles.pm>:
189 # 1) Name of relationship, DBIC will create accessor with this name
190 # 2) Name of the model class referenced by this relationship
191 # 3) Column name in *this* table
192 __PACKAGE__->belongs_to(user => 'MyApp::Schema::MyAppDB::Users', 'user_id');
196 # 1) Name of relationship, DBIC will create accessor with this name
197 # 2) Name of the model class referenced by this relationship
198 # 3) Column name in *this* table
199 __PACKAGE__->belongs_to(role => 'MyApp::Schema::MyAppDB::Roles', 'role_id');
202 The code for these three sets of updates is obviously very similar to
203 the edits we made to the C<Books>, C<Authors>, and C<BookAuthors>
204 classes created in Part 3.
206 Note that we do not need to make any change to the
207 C<lib/MyApp/Schema/MyAppDB.pm> schema file. It simple tells DBIC to
208 load all of the result source files it finds in below the
209 C<lib/MyApp/Schema/MyAppDB> directory, so it will automatically pick
210 up our new table information.
213 =head2 Sanity-Check Reload of Development Server
215 We aren't ready to try out the authentication just yet; we only want
216 to do a quick check to be sure our model loads correctly. Press
217 C<Ctrl-C> to kill the previous server instance (if it's still running)
220 $ script/myapp_server.pl
222 Look for the three new model objects in the startup debug output:
225 .-------------------------------------------------------------------+----------.
227 +-------------------------------------------------------------------+----------+
228 | MyApp::Controller::Books | instance |
229 | MyApp::Controller::Root | instance |
230 | MyApp::Model::MyAppDB | instance |
231 | MyApp::Model::MyAppDB::Author | class |
232 | MyApp::Model::MyAppDB::Books | class |
233 | MyApp::Model::MyAppDB::BookAuthors | class |
234 | MyApp::Model::MyAppDB::Roles | class |
235 | MyApp::Model::MyAppDB::Users | class |
236 | MyApp::Model::MyAppDB::UserRoles | class |
237 | MyApp::View::TT | instance |
238 '-------------------------------------------------------------------+----------'
241 Again, notice that your "result source" classes have been "re-loaded"
242 by Catalyst under C<MyApp::Model>.
245 =head2 Include Authentication and Session Plugins
247 Edit C<lib/MyApp.pm> and update it as follows (everything below
248 C<StackTrace> is new):
260 Session::Store::FastMmap
261 Session::State::Cookie
264 The C<Authentication> plugin supports Authentication while the
265 C<Session> plugins are required to maintain state across multiple HTTP
268 Note that the only required Authentication class is the main one. This
269 is a change that occurred in version 0.09999_01 of the
270 C<Authentication> plugin. You B<do not need> to specify a particular
271 Authentication::Store or Authentication::Credential plugin. Instead,
272 indicate the Store and Credential you want to use in your application
273 configuration (see below).
275 Note that there are several options for
276 L<Session::Store|Catalyst::Plugin::Session::Store>
277 (L<Session::Store::FastMmap|Catalyst::Plugin::Session::Store::FastMmap>
278 is generally a good choice if you are on Unix; try
279 L<Session::Store::File|Catalyst::Plugin::Session::Store::File> if you
280 are on Win32) -- consult
281 L<Session::Store|Catalyst::Plugin::Session::Store> and its subclasses
282 for additional information and options (for example to use a database-
283 backed session store).
286 =head2 Configure Authentication
288 Although C<__PACKAGE__-E<gt>config(name =E<gt> 'value');> is still
289 supported, newer Catalyst applications tend to place all configuration
290 information in C<myapp.yml> and automatically load this information
291 into C<MyApp-E<gt>config> using the
292 L<ConfigLoader|Catalyst::Plugin::ConfigLoader> plugin. Here, we need
293 to load several parameters that tell
294 L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication>
295 where to locate information in your database. To do this, edit the
296 C<myapp.yml> YAML and update it to match:
305 # Note this first definition would be the same as setting
306 # __PACKAGE__->config->{authentication}->{realms}->{dbic}
307 # ->{credential} = 'Password' in lib/MyApp.pm
308 # (IOW, each hash key becomes a "name:" in the YAML file).
310 # Specify that we are going to do password-based auth
312 # This is the name of the field in the users table with the
313 # password stored in it
314 password_field: password
315 # We are using an unencrypted password now
318 # Use DBIC to retrieve username, password & role information
320 # This is the model object created by Catalyst::Model::DBIC
321 # from your schema (you created 'MyAppDB::User' but as the
322 # Catalyst startup debug messages show, it was loaded as
323 # 'MyApp::Model::MyAppDB::Users').
324 # NOTE: Omit 'MyApp::Model' here just as you would when using
325 # '$c->model("MyAppDB::Users)'
326 user_class: MyAppDB::Users
327 # This is the name of the field in your 'users' table that
328 # contains the user's name
331 Inline comments in the code above explain how each field is being used.
333 B<TIP>: Although YAML uses a very simple and easy-to-ready format, it
334 does require the use of a consistent level of indenting. Be sure you
335 line up everything on a given 'level' with the same number of indents.
336 Also, be sure B<not> to use C<tab> characters (YAML does not support
337 them because they are handled inconsistently across editors).
340 =head2 Add Login and Logout Controllers
342 Use the Catalyst create script to create two stub controller files:
344 $ script/myapp_create.pl controller Login
345 $ script/myapp_create.pl controller Logout
347 B<NOTE>: You could easily use a single controller here. For example,
348 you could have a C<User> controller with both C<login> and C<logout>
349 actions. Remember, Catalyst is designed to be very flexible, and leaves
350 such matters up to you, the designer and programmer.
352 Then open C<lib/MyApp/Controller/Login.pm>, locate the C<sub index :
353 Private> method (this was automatically inserted by the helpers when we
354 created the Login controller above), and delete this line:
356 $c->response->body('Matched MyApp::Controller::Login in Login.');
358 Then update it to match:
366 sub index : Private {
369 # Get the username and password from form
370 my $username = $c->request->params->{username} || "";
371 my $password = $c->request->params->{password} || "";
373 # If the username and password values were found in form
374 if ($username && $password) {
375 # Attempt to log the user in
376 if ($c->authenticate({ username => $username,
377 password => $password} )) {
378 # If successful, then let them use the application
379 $c->response->redirect($c->uri_for('/books/list'));
382 # Set an error message
383 $c->stash->{error_msg} = "Bad username or password.";
387 # If either of above don't work out, send to the login page
388 $c->stash->{template} = 'login.tt2';
391 This controller fetches the C<username> and C<password> values from the
392 login form and attempts to authenticate the user. If successful, it
393 redirects the user to the book list page. If the login fails, the user
394 will stay at the login page but receive an error message. If the
395 C<username> and C<password> values are not present in the form, the
396 user will be taken to the empty login form.
398 Note that we could have used something like C<sub default :Private>;
399 however, the use of C<default> actions is discouraged because it does
400 not receive path args as with other actions. The recommended practice
401 is to only use C<default> in C<MyApp::Controller::Root>.
403 Another option would be to use something like
404 C<sub base :Path :Args(0) {...}> (where the C<...> refers to the login
405 code shown in C<sub index : Private> above). We are using C<sub base
406 :Path :Args(0) {...}> here to specifically match the URL C</login>.
407 C<Path> actions (aka, "literal actions") create URI matches relative to
408 the namespace of the controller where they are defined. Although
409 C<Path> supports arguments that allow relative and absolute paths to be
410 defined, here we use an empty C<Path> definition to match on just the
411 name of the controller itself. The method name, C<base>, is arbitrary.
412 We make the match even more specific with the C<:Args(0)> action
413 modifier -- this forces the match on I<only> C</login>, not
414 C</login/somethingelse>.
416 Next, update the corresponding method in
417 C<lib/MyApp/Controller/Logout.pm> to match:
425 sub index : Private {
428 # Clear the user's state
431 # Send the user to the starting point
432 $c->response->redirect($c->uri_for('/'));
435 As with the login controller, be sure to delete the
436 C<$c->response->body('Matched MyApp::Controller::Logout in Logout.');>
437 line of the C<sub index>.
440 =head2 Add a Login Form TT Template Page
442 Create a login form by opening C<root/src/login.tt2> and inserting:
444 [% META title = 'Login' %]
447 <form method="post" action=" [% Catalyst.uri_for('/login') %] ">
451 <td><input type="text" name="username" size="40" /></td>
455 <td><input type="password" name="password" size="40" /></td>
458 <td colspan="2"><input type="submit" name="submit" value="Submit" /></td>
464 =head2 Add Valid User Check
466 We need something that provides enforcement for the authentication
467 mechanism -- a I<global> mechanism that prevents users who have not
468 passed authentication from reaching any pages except the login page.
469 This is generally done via an C<auto> action/method (prior to Catalyst
470 v5.66, this sort of thing would go in C<MyApp.pm>, but starting in
471 v5.66, the preferred location is C<lib/MyApp/Controller/Root.pm>).
473 Edit the existing C<lib/MyApp/Controller/Root.pm> class file and insert
474 the following method:
478 Check if there is a user and, if not, forward to login page
482 # Note that 'auto' runs after 'begin' but before your actions and that
483 # 'auto' "chain" (all from application path to most specific class are run)
484 # See the 'Actions' section of 'Catalyst::Manual::Intro' for more info.
488 # Allow unauthenticated users to reach the login page. This
489 # allows anauthenticated users to reach any action in the Login
490 # controller. To lock it down to a single action, we could use:
491 # if ($c->action eq $c->controller('Login')->action_for('index'))
492 # to only allow unauthenticated access to the C<index> action we
494 if ($c->controller eq $c->controller('Login')) {
498 # If a user doesn't exist, force login
499 if (!$c->user_exists) {
500 # Dump a log message to the development server debug output
501 $c->log->debug('***Root::auto User not found, forwarding to /login');
502 # Redirect the user to the login page
503 $c->response->redirect($c->uri_for('/login'));
504 # Return 0 to cancel 'post-auto' processing and prevent use of application
508 # User found, so return 1 to continue with processing after this 'auto'
513 B<Note:> Catalyst provides a number of different types of actions,
514 such as C<Local>, C<Regex>, C<Private> and the new C<Path>. You
515 should refer to L<Catalyst::Manual::Intro|Catalyst::Manual::Intro> for
516 a more detailed explanation, but the following bullet points provide a
523 The majority of application have traditionally use C<Local> actions
524 for items that respond to user requests and C<Private> actions for
525 those that do not directly respond to user input.
529 Newer Catalyst applications tend to use C<Path> actions and the
530 C<Args> attribute because of their power and flexibility. You can
531 specify the path to match relative to the namespace of the current
532 module as an argument to C<Path>. For example C<Path('list')> in
533 C<lib/MyApp/Controller/Books.pm> would match on the URL
534 C<http://localhost:3000/books/list> but C<Path('/list')> would
535 match on C<http://localhost:3000/list>.
539 Automatic "chaining" of actions by the dispatcher is a powerful
540 feature that allows multiple methods to handle a single URL. See
541 L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained>
542 for more information on chained actions.
546 There are five types of build-in C<Private> actions: C<begin>, C<end>,
547 C<default>, C<index>, and C<auto>.
551 With C<begin>, C<end>, C<default>, C<index> private actions, only the
552 most specific action of each type will be called. For example, if you
553 define a C<begin> action in your controller it will I<override> a
554 C<begin> action in your application/root controller -- I<only> the
555 action in your controller will be called.
559 Unlike the other actions where only a single method is called for each
560 request, I<every> auto action along the chain of namespaces will be
561 called. Each C<auto> action will be called I<from the application/root
562 controller down through the most specific class>.
566 By placing the authentication enforcement code inside the C<auto> method
567 of C<lib/MyApp/Controller/Root.pm> (or C<lib/MyApp.pm>), it will be
568 called for I<every> request that is received by the entire application.
571 =head2 Displaying Content Only to Authenticated Users
573 Let's say you want to provide some information on the login page that
574 changes depending on whether the user has authenticated yet. To do
575 this, open C<root/src/login.tt2> in your editor and add the following
576 lines to the bottom of the file:
580 # This code illustrates how certain parts of the TT
581 # template will only be shown to users who have logged in
583 [% IF Catalyst.user_exists %]
584 Please Note: You are already logged in as '[% Catalyst.user.username %]'.
585 You can <a href="[% Catalyst.uri_for('/logout') %]">logout</a> here.
587 You need to log in to use this application.
590 Note that this whole block is a comment because the "#" appears
591 immediate after the "[%" (with no spaces in between). Although it
592 can be a handy way to temporarily "comment out" a whole block of
593 TT code, it's probably a little too subtle for use in "normal"
598 Although most of the code is comments, the middle few lines provide a
599 "you are already logged in" reminder if the user returns to the login
600 page after they have already authenticated. For users who have not yet
601 authenticated, a "You need to log in..." message is displayed (note the
602 use of an IF-THEN-ELSE construct in TT).
605 =head2 Try Out Authentication
607 Press C<Ctrl-C> to kill the previous server instance (if it's still
608 running) and restart it:
610 $ script/myapp_server.pl
612 B<IMPORTANT NOTE>: If you happen to be using Internet Explorer, you may
613 need to use the command C<script/myapp_server.pl -k> to enable the
614 keepalive feature in the development server. Otherwise, the HTTP
615 redirect on successful login may not work correctly with IE (it seems to
616 work without -k if you are running the web browser and development
617 server on the same machine). If you are using browser a browser other
618 than IE, it should work either way. If you want to make keepalive the
619 default, you can edit C<script/myapp_server.pl> and change the
620 initialization value for C<$keepalive> to C<1>. (You will need to do
621 this every time you create a new Catalyst application or rebuild the
622 C<myapp_server.pl> script.)
624 Now trying going to L<http://localhost:3000/books/list> and you should
625 be redirected to the login page, hitting Shift+Reload if necessary (the
626 "You are already logged in" message should I<not> appear -- if it does,
627 click the C<logout> button and try again). Note the C<***Root::auto User
628 not found...> debug message in the development server output. Enter
629 username C<test01> and password C<mypass>, and you should be taken to
632 Open C<root/src/books/list.tt2> and add the following lines to the
633 bottom (below the closing </table> tag):
636 <a href="[% Catalyst.uri_for('/login') %]">Login</a>
637 <a href="[% Catalyst.uri_for('form_create') %]">Create</a>
640 Reload your browser and you should now see a "Login" and "Create" links
641 at the bottom of the page (as mentioned earlier, you can update template
642 files without reloading the development server). Click the first link
643 to return to the login page. This time you I<should> see the "You are
644 already logged in" message.
646 Finally, click the C<You can logout here> link on the C</login> page.
647 You should stay at the login page, but the message should change to "You
648 need to log in to use this application."
651 =head1 USING PASSWORD HASHES
653 In this section we increase the security of our system by converting
654 from cleartext passwords to SHA-1 password hashes.
656 B<Note:> This section is optional. You can skip it and the rest of the
657 tutorial will function normally.
659 Note that even with the techniques shown in this section, the browser
660 still transmits the passwords in cleartext to your application. We are
661 just avoiding the I<storage> of cleartext passwords in the database by
662 using a SHA-1 hash. If you are concerned about cleartext passwords
663 between the browser and your application, consider using SSL/TLS, made
664 easy with the Catalyst plugin Catalyst::Plugin:RequireSSL.
667 =head2 Get a SHA-1 Hash for the Password
669 Catalyst uses the C<Digest> module to support a variety of hashing
670 algorithms. Here we will use SHA-1 (SHA = Secure Hash Algorithm).
671 First, we should compute the SHA-1 hash for the "mypass" password we are
672 using. The following command-line Perl script provides a "quick and
673 dirty" way to do this:
675 $ perl -MDigest::SHA -e 'print Digest::SHA::sha1_hex("mypass"), "\n"'
676 e727d1464ae12436e899a726da5b2f11d8381b26
679 B<Note:> You should probably modify this code for production use to
680 not read the password from the command line. By having the script
681 prompt for the cleartext password, it avoids having the password linger
682 in forms such as your C<.bash_history> files (assuming you are using
683 BASH as your shell). An example of such a script can be found in
687 =head2 Switch to SHA-1 Password Hashes in the Database
689 Next, we need to change the C<password> column of our C<users> table to
690 store this hash value vs. the existing cleartext password. Open
691 C<myapp03.sql> in your editor and enter:
694 -- Convert passwords to SHA-1 hashes
696 UPDATE users SET password = 'e727d1464ae12436e899a726da5b2f11d8381b26' WHERE id = 1;
697 UPDATE users SET password = 'e727d1464ae12436e899a726da5b2f11d8381b26' WHERE id = 2;
698 UPDATE users SET password = 'e727d1464ae12436e899a726da5b2f11d8381b26' WHERE id = 3;
700 Then use the following command to update the SQLite database:
702 $ sqlite3 myapp.db < myapp03.sql
704 B<Note:> We are using SHA-1 hashes here, but many other hashing
705 algorithms are supported. See C<Digest> for more information.
708 =head2 Enable SHA-1 Hash Passwords in
709 C<Catalyst::Plugin::Authentication::Store::DBIC>
711 Edit C<myapp.yml> and update it to match (the C<password_type> and
712 C<password_hash_type> are new, everything else is the same):
721 # Note this first definition would be the same as setting
722 # __PACKAGE__->config->{authentication}->{realms}->{dbic}
723 # ->{credential} = 'Password' in lib/MyApp.pm
724 # (IOW, each hash key becomes a "name:" in the YAML file).
726 # Specify that we are going to do password-based auth
728 # This is the name of the field in the users table with the
729 # password stored in it
730 password_field: password
731 # Switch to more secure hashed passwords
732 password_type: hashed
733 # Use the SHA-1 hashing algorithm
734 password_hash_type: SHA-1
736 # Use DBIC to retrieve username, password & role information
738 # This is the model object created by Catalyst::Model::DBIC
739 # from your schema (you created 'MyAppDB::User' but as the
740 # Catalyst startup debug messages show, it was loaded as
741 # 'MyApp::Model::MyAppDB::Users').
742 # NOTE: Omit 'MyApp::Model' here just as you would when using
743 # '$c->model("MyAppDB::Users)'
744 user_class: MyAppDB::Users
745 # This is the name of the field in your 'users' table that
746 # contains the user's name
750 =head2 Try Out the Hashed Passwords
752 Press C<Ctrl-C> to kill the previous server instance (if it's still
753 running) and restart it:
755 $ script/myapp_server.pl
757 You should now be able to go to L<http://localhost:3000/books/list> and
758 login as before. When done, click the "Logout" link on the login page
759 (or point your browser at L<http://localhost:3000/logout>).
762 =head1 USING THE SESSION FOR FLASH
764 As discussed in Part 3 of the tutorial, C<flash> allows you to set
765 variables in a way that is very similar to C<stash>, but it will
766 remain set across multiple requests. Once the value is read, it
767 is cleared (unless reset). Although C<flash> has nothing to do with
768 authentication, it does leverage the same session plugins. Now that
769 those plugins are enabled, let's go back and improve the "delete
770 and redirect with query parameters" code seen at the end of the
771 L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD> part of the
774 First, open C<lib/MyApp/Controller/Books.pm> and modify C<sub delete>
775 to match the following (everything after the model search line of code
785 # $id = primary key of book to delete
786 my ($self, $c, $id) = @_;
788 # Search for the book and then delete it
789 $c->model('MyAppDB::Books')->search({id => $id})->delete_all;
791 # Use 'flash' to save information across requests until it's read
792 $c->flash->{status_msg} = "Book deleted";
794 # Redirect the user back to the list page
795 $c->response->redirect($c->uri_for('/books/list'));
798 Next, open C<root/lib/site/layout> and update the TT code to pull from
799 flash vs. the C<status_msg> query parameter:
801 <div id="header">[% PROCESS site/header %]</div>
804 <span class="message">[% status_msg || Catalyst.flash.status_msg %]</span>
805 <span class="error">[% error_msg %]</span>
809 <div id="footer">[% PROCESS site/footer %]</div>
814 Restart the development server and point your browser to
815 L<http://localhost:3000/books/url_create/Test/1/4> to create an extra
816 several books. Click the "Return to list" link and delete one of the
817 "Test" books you just added. The C<flash> mechanism should retain our
818 "Book deleted" status message across the redirect.
820 B<NOTE:> While C<flash> will save information across multiple requests,
821 I<it does get cleared the first time it is read>. In general, this is
822 exactly what you want -- the C<flash> message will get displayed on
823 the next screen where it's appropriate, but it won't "keep showing up"
824 after that first time (unless you reset it). Please refer to
825 L<Catalyst::Plugin::Session|Catalyst::Plugin::Session> for additional
828 =head2 Switch To Flash-To-Stash
830 Although the a use of flash above is certainly an improvement over the
831 C<status_msg> we employed in Part 4 of the tutorial, the C<status_msg
832 || Catalyst.flash.status_msg> statement is a little ugly. A nice
833 alternative is to use the C<flash_to_stash> feature that automatically
834 copies the content of flash to stash. This makes your code controller
835 and template code work regardless of where it was directly access, a
836 forward, or a redirect. To enable C<flash_to_stash>, you can either
837 set the value in C<lib/MyApp.pm> by changing the default
838 C<__PACKAGE__-E<gt>config> setting to something like:
842 session => {flash_to_stash => 1}
845 B<or> add the following to C<myapp.yml>:
850 The C<__PACKAGE__-E<gt>config> option is probably preferable here
851 since it's not something you will want to change at runtime without it
852 possibly breaking some of your code.
854 Then edit C<root/lib/site/layout> and change the C<status_msg> line
855 to look like the following:
857 <span class="message">[% status_msg %]</span>
859 Restart the development server and go to
860 L<http://localhost:3000/books/list> in your browser. Delete another
861 of the "Test" books you added in the previous step. Flash should still
862 maintain the status message across the redirect even though you are no
863 longer explicitly accessing C<Catalyst.flash>.
868 Kennedy Clark, C<hkclark@gmail.com>
870 Please report any errors, issues or suggestions to the author. The
871 most recent version of the Catalyst Tutorial can be found at
872 L<http://dev.catalyst.perl.org/repos/Catalyst/trunk/Catalyst-Manual/lib/Catalyst/Manual/Tutorial/>.
874 Copyright 2006, Kennedy Clark, under Creative Commons License
875 (L<http://creativecommons.org/licenses/by-nc-sa/2.5/>).