3 Catalyst::Manual::Tutorial::BasicCRUD - Catalyst Tutorial - Part 4: Basic CRUD
8 This is B<Part 4 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>
32 L<Authentication|Catalyst::Manual::Tutorial::Authentication>
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 This part of the tutorial builds on the fairly primitive application
60 created in Part 3 to add basic support for Create, Read, Update, and
61 Delete (CRUD) of C<Book> objects. Note that the 'list' function in Part
62 2 already implements the Read portion of CRUD (although Read normally
63 refers to reading a single object; you could implement full read
64 functionality using the techniques introduced below). This section will
65 focus on the Create and Delete aspects of CRUD. More advanced
66 capabilities, including full Update functionality, will be addressed in
69 Although this part of the tutorial will show you how to build CRUD
70 functionality yourself, another option is to use a "CRUD builder" type
71 of tool to automate the process. You get less control, but it's quick
72 and easy. For example, see
73 L<CatalystX::ListFramework::Builder|CatalystX::ListFramework::Builder>,
74 L<CatalystX::CRUD|CatalystX::CRUD>, and
75 L<CatalystX::CRUD::YUI|CatalystX::CRUD::YUI>.
77 You can checkout the source code for this example from the catalyst
78 subversion repository as per the instructions in
79 L<Catalyst::Manual::Tutorial::Intro|Catalyst::Manual::Tutorial::Intro>.
82 =head1 FORMLESS SUBMISSION
84 Our initial attempt at object creation will utilize the "URL
85 arguments" feature of Catalyst (we will employ the more common form-
86 based submission in the sections that follow).
89 =head2 Include a Create Action in the Books Controller
91 Edit C<lib/MyApp/Controller/Books.pm> and enter the following method:
95 Create a book with the supplied title, rating, and author
99 sub url_create : Local {
100 # In addition to self & context, get the title, rating, &
101 # author_id args from the URL. Note that Catalyst automatically
102 # puts extra information after the "/<controller_name>/<action_name/"
104 my ($self, $c, $title, $rating, $author_id) = @_;
106 # Call create() on the book model object. Pass the table
107 # columns/field values we want to set as hash values
108 my $book = $c->model('DB::Books')->create({
113 # Add a record to the join table for this book, mapping to
115 $book->add_to_book_authors({author_id => $author_id});
116 # Note: Above is a shortcut for this:
117 # $book->create_related('book_authors', {author_id => $author_id});
119 # Assign the Book object to the stash for display in the view
120 $c->stash->{book} = $book;
122 # This is a hack to disable XSUB processing in Data::Dumper
123 # (it's used in the view). This is a work-around for a bug in
124 # the interaction of some versions or Perl, Data::Dumper & DBIC.
125 # You won't need this if you aren't using Data::Dumper (or if
126 # you are running DBIC 0.06001 or greater), but adding it doesn't
127 # hurt anything either.
128 $Data::Dumper::Useperl = 1;
130 # Set the TT template to use
131 $c->stash->{template} = 'books/create_done.tt2';
134 Notice that Catalyst takes "extra slash-separated information" from the
135 URL and passes it as arguments in C<@_>. The C<url_create> action then
136 uses a simple call to the DBIC C<create> method to add the requested
137 information to the database (with a separate call to
138 C<add_to_book_authors> to update the join table). As do virtually all
139 controller methods (at least the ones that directly handle user input),
140 it then sets the template that should handle this request.
143 =head2 Include a Template for the C<url_create> Action:
145 Edit C<root/src/books/create_done.tt2> and then enter:
147 [% # Use the TT Dumper plugin to Data::Dumper variables to the browser -%]
148 [% # Not a good idea for production use, though. :-) 'Indent=1' is -%]
149 [% # optional, but prevents "massive indenting" of deeply nested objects -%]
150 [% USE Dumper(Indent=1) -%]
152 [% # Set the page title. META can 'go back' and set values in templates -%]
153 [% # that have been processed 'before' this template (here it's for -%]
154 [% # root/lib/site/html and root/lib/site/header). Note that META on -%]
155 [% # simple strings (e.g., no variable interpolation). -%]
156 [% META title = 'Book Created' %]
158 [% # Output information about the record that was added. First title. -%]
159 <p>Added book '[% book.title %]'
161 [% # Output the last name of the first author. This is complicated by an -%]
162 [% # issue in TT 2.15 where blessed hash objects are not handled right. -%]
163 [% # First, fetch 'book.authors' from the DB once. -%]
164 [% authors = book.authors %]
165 [% # Now use IF statements to test if 'authors.first' is "working". If so, -%]
166 [% # we use it. Otherwise we use a hack that seems to keep TT 2.15 happy. -%]
167 by '[% authors.first.last_name IF authors.first;
168 authors.list.first.value.last_name IF ! authors.first %]'
170 [% # Output the rating for the book that was added -%]
171 with a rating of [% book.rating %].</p>
173 [% # Provide a link back to the list page -%]
174 [% # 'uri_for()' builds a full URI; e.g., 'http://localhost:3000/books/list' -%]
175 <p><a href="[% c.uri_for('/books/list') %]">Return to list</a></p>
177 [% # Try out the TT Dumper (for development only!) -%]
179 Dump of the 'book' variable:
180 [% Dumper.dump(book) %]
183 The TT C<USE> directive allows access to a variety of plugin modules
184 (TT plugins, that is, not Catalyst plugins) to add extra functionality
185 to the base TT capabilities. Here, the plugin allows
186 L<Data::Dumper|Data::Dumper> "pretty printing" of objects and
187 variables. Other than that, the rest of the code should be familiar
188 from the examples in Part 3.
191 =head2 Try the C<url_create> Feature
193 If the application is still running from before, use C<Ctrl-C> to kill
194 it. Then restart the server:
196 $ DBIC_TRACE=1 script/myapp_server.pl
198 Note that new path for C</books/url_create> appears in the startup debug
201 B<TIP>: You can use C<script/myapp_server.pl -r> to have the development
202 server auto-detect changed files and reload itself (if your browser acts
203 odd, you should also try throwing in a C<-k>). If you make changes to
204 the TT templates only, you do not need to reload the development server
205 (only changes to "compiled code" such as Controller and Model C<.pm>
206 files require a reload).
208 Next, use your browser to enter the following URL:
210 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
212 Your browser should display "Added book 'TCPIP_Illustrated_Vol-2' by
213 'Stevens' with a rating of 5." along with a dump of the new book model
214 object. You should also see the following DBIC debug messages displayed
215 in the development server log messages if you have DBIC_TRACE set:
217 INSERT INTO books (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
218 INSERT INTO book_authors (author_id, book_id) VALUES (?, ?): `4', `6'
219 SELECT author.id, author.first_name, author.last_name
220 FROM book_authors me JOIN authors author
221 ON ( author.id = me.author_id ) WHERE ( me.book_id = ? ): '6'
223 The C<INSERT> statements are obviously adding the book and linking it to
224 the existing record for Richard Stevens. The C<SELECT> statement results
225 from DBIC automatically fetching the book for the C<Dumper.dump(book)>.
227 If you then click the "Return to list" link, you should find that
228 there are now six books shown (if necessary, Shift+Reload or
229 Ctrl+Reload your browser at the C</books/list> page).
232 =head1 CONVERT TO A CHAINED ACTION
234 Although the example above uses the same C<Local> action type for the
235 method that we saw in the previous part of the tutorial, there is an
236 alternate approach that allows us to be more specific while also
237 paving the way for more advanced capabilities. Change the method
238 declaration for C<url_create> in C<lib/MyApp/Controller/Books.pm> you
239 entered above to match the following:
241 sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
243 This converts the method to take advantage of the Chained
244 action/dispatch type. Chaining let's you have a single URL
245 automatically dispatch to several controller methods, each of which
246 can have precise control over the number of arguments that it will
247 receive. A chain can essentially be thought of having three parts --
248 a beginning, a middle and an end. The bullets below summarize the key
249 points behind each of these parts of a chain:
263 B<Use "C<:Chained('/')>" to start a chain>
267 Get arguments through C<CaptureArgs()>
271 Specify the path to match with C<PathPart()>
284 Link to previous part of the chain with C<:Chained('_name_')>
288 Get arguments through C<CaptureArgs()>
292 Specify the path to match with C<PathPart()>
305 Link to previous part of the chain with C<:Chained('_name_')>
309 B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
313 Specify the path to match with C<PathPart()>
320 In our C<url_create> method above, we have combined all 3 parts into a
321 single method: C<:Chained('/')> to start the chain,
322 C<:PathPart('books/url_create')> to specify the base URL to match,
323 along with C<:Args(3)> to capture exactly 3 arguments and also end the
326 As we will see shortly, a chain can consist of as many "links" as you
327 wish, with each part capturing some arguments and doing some work
328 along the way. We will continue to use the Chained action type in this
329 part of the tutorial and explore slightly more advanced capabilities
330 with the base method and delete feature below. But Chained dispatch
331 is capable of far more. For additional information, see
332 L<Catalyst::Manual::Intro/Action types>,
333 L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained>,
334 and the 2006 advent calendar entry on the subject:
335 L<http://www.catalystframework.org/calendar/2006/10>.
338 =head2 Try the Chained Action
340 If you look back at the development server startup logs from your
341 initial version of the C<url_create> method (the one using the
342 C<:Local> attribute), you will notice that it produced output similar
345 [debug] Loaded Path actions:
346 .-------------------------------------+--------------------------------------.
348 +-------------------------------------+--------------------------------------+
351 | /books | /books/index |
352 | /books/list | /books/list |
353 | /books/url_create | /books/url_create |
354 '-------------------------------------+--------------------------------------'
356 Now start the development server with our basic chained method in
357 place and the startup debug output should change to something along
358 the lines of the following:
360 [debug] Loaded Path actions:
361 .-------------------------------------+--------------------------------------.
363 +-------------------------------------+--------------------------------------+
366 | /books | /books/index |
367 | /books/list | /books/list |
368 '-------------------------------------+--------------------------------------'
370 [debug] Loaded Chained actions:
371 .-------------------------------------+--------------------------------------.
372 | Path Spec | Private |
373 +-------------------------------------+--------------------------------------+
374 | /books/url_create/*/*/* | /books/url_create |
375 '-------------------------------------+--------------------------------------'
377 C<url_create> has disappeared form the "Loaded Path actions" section
378 but it now shows up under the newly created "Loaded Chained actions"
379 section. And, the "/*/*/*" portion clearly shows that we have
380 specified that 3 arguments are required.
382 As with our non-chained version of C<url_create>, use your browser to
383 enter the following URL:
385 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
387 You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
388 'Stevens' with a rating of 5." along with a dump of the new book model
389 object. Click the "Return to list" link, you should find that there
390 are now seven books shown (two copies of TCPIP_Illustrated_Vol-2).
393 =head2 Refactor to Use a "Base" Method to Start The Chains
395 Let's make a quick update to our initial Chained action to show a
396 little more of the power of chaining. First, open
397 C<lib/MyApp/Controller/Books.pm> in your editor and add the following
402 Can place common logic to start chained dispatch here
406 sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
409 $c->log->debug('*** INSIDE BASE METHOD ***');
412 Although we only use the C<base> method to create a log message, we
413 could obviously do any number of things here. For example, if your
414 controller always needs a book ID as it's first argument, you could
415 have the base method capture that argument (with C<:CaptureArgs(1)>)
416 and use it to pull the book object with that ID from the database and
417 leave it in the stash for later parts of your chains to then act upon.
419 In our case, let's modify our C<url_create> method to first call
420 C<base>. Open up C<lib/MyApp/Controller/Books.pm> and edit the
421 declaration for C<url_create> to match the following:
423 sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
425 Next, let's try out our refactored chain. Restart the development
426 server and notice that our "Loaded Chained actions" section has
429 [debug] Loaded Chained actions:
430 .-------------------------------------+--------------------------------------.
431 | Path Spec | Private |
432 +-------------------------------------+--------------------------------------+
433 | /books/url_create/*/*/* | /books/base (0) |
434 | | => /books/url_create |
435 '-------------------------------------+--------------------------------------'
437 The "Path Spec" is the same, but now it maps to two Private actions as
440 Once again, enter the following URL into your browser:
442 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
444 The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
445 rating of 5." and dump of the new book object should appear. Also
446 notice the extra debug message in the development server output from
447 the C<base> method. Click the "Return to list" link, you should find
448 that there are now eight books shown.
451 =head1 MANUALLY BUILDING A CREATE FORM
453 Although the C<url_create> action in the previous step does begin to
454 reveal the power and flexibility of both Catalyst and DBIC, it's
455 obviously not a very realistic example of how users should be expected
456 to enter data. This section begins to address that concern.
459 =head2 Add Method to Display The Form
461 Edit C<lib/MyApp/Controller/Books.pm> and add the following method:
465 Display form to collect information for book to create
469 sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
472 # Set the TT template to use
473 $c->stash->{template} = 'books/form_create.tt2';
476 This action simply invokes a view containing a book creation form.
479 =head2 Add a Template for the Form
481 Open C<root/src/books/form_create.tt2> in your editor and enter:
483 [% META title = 'Manual Form Book Create' -%]
485 <form method="post" action="[% c.uri_for('form_create_do') %]">
487 <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
488 <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
489 <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
491 <input type="submit" name="Submit" value="Submit">
494 Note that we have specified the target of the form data as
495 C<form_create_do>, the method created in the section that follows.
498 =head2 Add a Method to Process Form Values and Update Database
500 Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
501 save the form information to the database:
503 =head2 form_create_do
505 Take information from form and add to database
509 sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
512 # Retrieve the values from the form
513 my $title = $c->request->params->{title} || 'N/A';
514 my $rating = $c->request->params->{rating} || 'N/A';
515 my $author_id = $c->request->params->{author_id} || '1';
518 my $book = $c->model('DB::Books')->create({
522 # Handle relationship with author
523 $book->add_to_book_authors({author_id => $author_id});
525 # Store new model object in stash
526 $c->stash->{book} = $book;
528 # Avoid Data::Dumper issue mentioned earlier
529 # You can probably omit this
530 $Data::Dumper::Useperl = 1;
532 # Set the TT template to use
533 $c->stash->{template} = 'books/create_done.tt2';
537 =head2 Test Out The Form
539 If the application is still running from before, use C<Ctrl-C> to kill
540 it. Then restart the server:
542 $ script/myapp_server.pl
544 Notice that the server startup log reflects the two new chained
545 methods that we added:
547 [debug] Loaded Chained actions:
548 .-------------------------------------+--------------------------------------.
549 | Path Spec | Private |
550 +-------------------------------------+--------------------------------------+
551 | /books/form_create | /books/base (0) |
552 | | => /books/form_create |
553 | /books/form_create_do | /books/base (0) |
554 | | => /books/form_create_do |
555 | /books/url_create/*/*/* | /books/base (0) |
556 | | => /books/url_create |
557 '-------------------------------------+--------------------------------------'
559 Point your browser to L<http://localhost:3000/books/form_create> and
560 enter "TCP/IP Illustrated, Vol 3" for the title, a rating of 5, and an
561 author ID of 4. You should then see the output of the same
562 C<create_done.tt2> template seen in earlier examples. Finally, click
563 "Return to list" to view the full list of books.
565 B<Note:> Having the user enter the primary key ID for the author is
566 obviously crude; we will address this concern with a drop-down list in
570 =head1 A SIMPLE DELETE FEATURE
572 Turning our attention to the delete portion of CRUD, this section
573 illustrates some basic techniques that can be used to remove information
577 =head2 Include a Delete Link in the List
579 Edit C<root/src/books/list.tt2> and update it to the following (two
580 sections have changed: 1) the additional '<th>Links</th>' table header,
581 and 2) the four lines for the Delete link near the bottom).
583 [% # This is a TT comment. The '-' at the end "chomps" the newline. You won't -%]
584 [% # see this "chomping" in your browser because HTML ignores blank lines, but -%]
585 [% # it WILL eliminate a blank line if you view the HTML source. It's purely -%]
586 [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
588 [% # Provide a title to root/lib/site/header -%]
589 [% META title = 'Book List' -%]
592 <tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
593 [% # Display each book in a table row %]
594 [% FOREACH book IN books -%]
596 <td>[% book.title %]</td>
597 <td>[% book.rating %]</td>
599 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
600 [% # loop in 'side effect notation' to load just the last names of the -%]
601 [% # authors into the list. Note that the 'push' TT vmethod does not -%]
602 [% # a value, so nothing will be printed here. But, if you have something -%]
603 [% # in TT that does return a method and you don't want it printed, you -%]
604 [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to -%]
605 [% # call it and discard the return value. -%]
607 tt_authors.push(author.last_name) FOREACH author = book.authors %]
608 [% # Now use a TT 'virtual method' to display the author count in parens -%]
609 ([% tt_authors.size %])
610 [% # Use another TT vmethod to join & print the names & comma separators -%]
611 [% tt_authors.join(', ') %]
614 [% # Add a link to delete a book %]
615 <a href="[% c.uri_for('delete', book.id) %]">Delete</a>
621 The additional code is obviously designed to add a new column to the
622 right side of the table with a C<Delete> "button" (for simplicity,
623 links will be used instead of full HTML buttons).
625 B<Note:> You should use more than just a simple link with your
626 applications. Consider using some sort of of confirmation page
627 (typically with unique actions in your controller for both the
628 confirmation and the actual delete operation). Also, you should try
629 to use an HTTP POST operation (versus the GET used here) for
630 operations that change the state of your application (e.g., the
634 =head2 Add a Delete Action to the Controller
636 Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
645 sub delete :Chained('base') :PathPart('delete') :Args(1) {
646 # $id = primary key of book to delete
647 my ($self, $c, $id) = @_;
649 # Search for the book and then delete it
650 $c->model('DB::Books')->search({id => $id})->delete_all;
652 # Set a status message to be displayed at the top of the view
653 $c->stash->{status_msg} = "Book deleted.";
655 # Forward to the list action/method in this controller
659 This method first deletes the book with the specified primary key ID.
660 However, it also removes the corresponding entry from the
661 C<book_authors> table. Note that C<delete_all> was used instead of
662 C<delete>: whereas C<delete_all> also removes the join table entries in
663 C<book_authors>, C<delete> does not (only use C<delete_all> if you
664 really need the cascading deletes... otherwise you are wasting resources).
666 Then, rather than forwarding to a "delete done" page as we did with the
667 earlier create example, it simply sets the C<status_msg> to display a
668 notification to the user as the normal list view is rendered.
670 The C<delete> action uses the context C<forward> method to return the
671 user to the book list. The C<detach> method could have also been used.
672 Whereas C<forward> I<returns> to the original action once it is
673 completed, C<detach> does I<not> return. Other than that, the two are
677 =head2 Try the Delete Feature
679 If the application is still running from before, use C<Ctrl-C> to kill
680 it. Then restart the server:
682 $ script/myapp_server.pl
684 The C<delete> method now appears in the "Loaded Chained actions" section
685 of the startup debug output:
687 [debug] Loaded Chained actions:
688 .-------------------------------------+--------------------------------------.
689 | Path Spec | Private |
690 +-------------------------------------+--------------------------------------+
691 | /books/delete/* | /books/base (0) |
692 | | => /books/delete |
693 | /books/form_create | /books/base (0) |
694 | | => /books/form_create |
695 | /books/form_create_do | /books/base (0) |
696 | | => /books/form_create_do |
697 | /books/url_create/*/*/* | /books/base (0) |
698 | | => /books/url_create |
699 '-------------------------------------+--------------------------------------'
701 Then point your browser to L<http://localhost:3000/books/list> and click
702 the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
703 "Book deleted" status message should display at the top of the page,
704 along with a list of the eight remaining books.
707 =head2 Fixing a Dangerous URL
709 Note the URL in your browser once you have performed the deletion in the
710 prior step -- it is still referencing the delete action:
712 http://localhost:3000/books/delete/6
714 What if the user were to press reload with this URL still active? In
715 this case the redundant delete is harmless, but in other cases this
716 could clearly be extremely dangerous.
718 We can improve the logic by converting to a redirect. Unlike
719 C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform
720 a server-side alteration in the flow of processing, a redirect is a
721 client-side mechanism that causes the browser to issue an entirely
722 new request. As a result, the URL in the browser is updated to match
723 the destination of the redirection URL.
725 To convert the forward used in the previous section to a redirect,
726 open C<lib/MyApp/Controller/Books.pm> and edit the existing
727 C<sub delete> method to match:
735 sub delete :Chained('base') :PathPart('delete') :Args(1) {
736 # $id = primary key of book to delete
737 my ($self, $c, $id) = @_;
739 # Search for the book and then delete it
740 $c->model('DB::Books')->search({id => $id})->delete_all;
742 # Set a status message to be displayed at the top of the view
743 $c->stash->{status_msg} = "Book deleted.";
745 # Redirect the user back to the list page
746 $c->response->redirect($c->uri_for('/books/list'));
750 =head2 Try the Delete and Redirect Logic
752 Restart the development server and point your browser to
753 L<http://localhost:3000/books/list> and delete the first copy of the
754 remaining two "TCPIP_Illustrated_Vol-2" books. The URL in your
755 browser should return to the L<http://localhost:3000/books/list> URL,
756 so that is an improvement, but notice that I<no green "Book deleted"
757 status message is displayed>. Because the stash is reset on every
758 request (and a redirect involves a second request), the C<status_msg>
759 is cleared before it can be displayed.
762 =head2 Using C<uri_for> to Pass Query Parameters
764 There are several ways to pass information across a redirect. One
765 option is to use the C<flash> technique that we will see in Part 5 of
766 the tutorial; however, here we will pass the information via query
767 parameters on the redirect itself. Open
768 C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
769 method to match the following:
777 sub delete :Chained('base') :PathPart('delete') :Args(1) {
778 # $id = primary key of book to delete
779 my ($self, $c, $id) = @_;
781 # Search for the book and then delete it
782 $c->model('DB::Books')->search({id => $id})->delete_all;
784 # Redirect the user back to the list page with status msg as an arg
785 $c->response->redirect($c->uri_for('/books/list',
786 {status_msg => "Book deleted."}));
789 This modification simply leverages the ability of C<uri_for> to include
790 an arbitrary number of name/value pairs in a hash reference. Next, we
791 need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
796 [%# Status and error messages %]
797 <span class="message">[% status_msg || c.request.params.status_msg %]</span>
798 <span class="error">[% error_msg %]</span>
799 [%# This is where TT will stick all of your template's contents. -%]
801 </div><!-- end content -->
804 Although the sample above only shows the C<content> div, leave the
805 rest of the file intact -- the only change we made to the C<wrapper.tt2>
806 was to add "C<|| c.request.params.status_msg>" to the
807 C<E<lt>span class="message"E<gt>> line.
810 =head2 Try the Delete and Redirect With Query Param Logic
812 Restart the development server and point your browser to
813 L<http://localhost:3000/books/list>. Then delete the remaining copy
814 of "TCPIP_Illustrated_Vol-2". The green "Book deleted" status message
817 B<NOTE:> Another popular method for maintaining server-side
818 information across a redirect is to use the C<flash> technique we
819 discuss in the next part of the tutorial,
820 L<Authentication|Catalyst::Manual::Tutorial::Authentication>. While
821 C<flash> is a "slicker" mechanism in that it's all handled by the
822 server and doesn't "pollute" your URLs, B<it is important to note that
823 C<flash> can lead to situations where the wrong information shows up
824 in the wrong browser window if the user has multiple windows or
825 browser tabs open.> (For example, Window A causes something to be
826 placed in the stash, but before that window performs a redirect,
827 Window B makes a request to the server and gets the status information
828 that should really go to Window A.) For this reason, you may wish
829 to use the "query param" technique shown here in your applications.
834 Kennedy Clark, C<hkclark@gmail.com>
836 Please report any errors, issues or suggestions to the author. The
837 most recent version of the Catalyst Tutorial can be found at
838 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.70/trunk/lib/Catalyst/Manual/Tutorial/>.
840 Copyright 2006-2008, Kennedy Clark, under Creative Commons License
841 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).