3 Catalyst::Manual::Tutorial::04_BasicCRUD - Catalyst Tutorial - Chapter 4: Basic CRUD
8 This is B<Chapter 4 of 10> for the Catalyst tutorial.
10 L<Tutorial Overview|Catalyst::Manual::Tutorial>
16 L<Introduction|Catalyst::Manual::Tutorial::01_Intro>
20 L<Catalyst Basics|Catalyst::Manual::Tutorial::02_CatalystBasics>
24 L<More Catalyst Basics|Catalyst::Manual::Tutorial::03_MoreCatalystBasics>
32 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>
36 L<Authorization|Catalyst::Manual::Tutorial::06_Authorization>
40 L<Debugging|Catalyst::Manual::Tutorial::07_Debugging>
44 L<Testing|Catalyst::Manual::Tutorial::08_Testing>
48 L<Advanced CRUD|Catalyst::Manual::Tutorial::09_AdvancedCRUD>
52 L<Appendices|Catalyst::Manual::Tutorial::10_Appendices>
59 This chapter of the tutorial builds on the fairly primitive
60 application created in Chapter 3 to add basic support for Create,
61 Read, Update, and Delete (CRUD) of C<Book> objects. Note that the
62 'list' function in Chapter 2 already implements the Read portion of
63 CRUD (although Read normally refers to reading a single object; you
64 could implement full Read functionality using the techniques
65 introduced below). This section will focus on the Create and Delete
66 aspects of CRUD. More advanced capabilities, including full Update
67 functionality, will be addressed in Chapter 9.
69 Although this chapter 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 check out the source code for this example from the Catalyst
78 Subversion repository as per the instructions in
79 L<Catalyst::Manual::Tutorial::01_Intro|Catalyst::Manual::Tutorial::01_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/"
103 # into @_. The args are separated by the '/' char on the URL.
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::Book')->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 # Set the TT template to use
123 $c->stash->{template} = 'books/create_done.tt2';
126 Notice that Catalyst takes "extra slash-separated information" from the
127 URL and passes it as arguments in C<@_>. The C<url_create> action then
128 uses a simple call to the DBIC C<create> method to add the requested
129 information to the database (with a separate call to
130 C<add_to_book_authors> to update the join table). As do virtually all
131 controller methods (at least the ones that directly handle user input),
132 it then sets the template that should handle this request.
135 =head2 Include a Template for the 'url_create' Action:
137 Edit C<root/src/books/create_done.tt2> and then enter:
139 [% # Use the TT Dumper plugin to Data::Dumper variables to the browser -%]
140 [% # Not a good idea for production use, though. :-) 'Indent=1' is -%]
141 [% # optional, but prevents "massive indenting" of deeply nested objects -%]
142 [% USE Dumper(Indent=1) -%]
144 [% # Set the page title. META can 'go back' and set values in templates -%]
145 [% # that have been processed 'before' this template (here it's for -%]
146 [% # root/lib/site/html and root/lib/site/header). Note that META only -%]
147 [% # works on simple/static strings (i.e. there is no variable -%]
148 [% # interpolation). -%]
149 [% META title = 'Book Created' %]
151 [% # Output information about the record that was added. First title. -%]
152 <p>Added book '[% book.title %]'
154 [% # Output the last name of the first author. -%]
155 by '[% book.authors.first.last_name %]'
157 [% # Output the rating for the book that was added -%]
158 with a rating of [% book.rating %].</p>
160 [% # Provide a link back to the list page -%]
161 [% # 'uri_for()' builds a full URI; e.g., 'http://localhost:3000/books/list' -%]
162 <p><a href="[% c.uri_for('/books/list') %]">Return to list</a></p>
164 [% # Try out the TT Dumper (for development only!) -%]
166 Dump of the 'book' variable:
167 [% Dumper.dump(book) %]
170 The TT C<USE> directive allows access to a variety of plugin modules
171 (TT plugins, that is, not Catalyst plugins) to add extra functionality
172 to the base TT capabilities. Here, the plugin allows
173 L<Data::Dumper|Data::Dumper> "pretty printing" of objects and
174 variables. Other than that, the rest of the code should be familiar
175 from the examples in Chapter 3.
177 Note: If you are using TT v2.15 you will need to change the code that
178 outputs the "last name for the first author" above to match this:
180 [% authors = book.authors %]
181 by '[% authors.first.last_name IF authors.first;
182 authors.list.first.value.last_name IF ! authors.first %]'
184 to get around an issue in TT v2.15 where blessed hash objects were not
185 handled correctly. But, if you are still using v2.15, it's probably
186 time to upgrade (v2.15 is exactly 3 years old on the day I'm typing
187 this). If you are following along in Debian, then you should be on at
188 least v2.20. You can test your version of Template Toolkit with the
191 perl -MTemplate -e 'print "$Template::VERSION\n"'
194 =head2 Try the 'url_create' Feature
196 If the application is still running from before, use C<Ctrl-C> to kill
197 it. Then restart the server:
199 $ DBIC_TRACE=1 script/myapp_server.pl
201 Note that new path for C</books/url_create> appears in the startup debug
204 B<TIP>: You can use C<script/myapp_server.pl -r> to have the development
205 server auto-detect changed files and reload itself (if your browser acts
206 odd, you should also try throwing in a C<-k>). If you make changes to
207 the TT templates only, you do not need to reload the development server
208 (only changes to "compiled code" such as Controller and Model C<.pm>
209 files require a reload).
211 Next, use your browser to enter the following URL:
213 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
215 Your browser should display "Added book 'TCPIP_Illustrated_Vol-2' by
216 'Stevens' with a rating of 5." along with a dump of the new book model
217 object as it was returned by DBIC. You should also see the following
218 DBIC debug messages displayed in the development server log messages
219 if you have DBIC_TRACE set:
221 INSERT INTO book (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
222 INSERT INTO book_author (author_id, book_id) VALUES (?, ?): `4', `6'
224 The C<INSERT> statements are obviously adding the book and linking it to
225 the existing record for Richard Stevens. The C<SELECT> statement results
226 from DBIC automatically fetching the book for the C<Dumper.dump(book)>.
228 If you then click the "Return to list" link, you should find that
229 there are now six books shown (if necessary, Shift+Reload or
230 Ctrl+Reload your browser at the C</books/list> page). You should now
231 see the six DBIC debug messages similar to the following (where
234 SELECT author.id, author.first_name, author.last_name \
235 FROM book_author me JOIN author author \
236 ON author.id = me.author_id WHERE ( me.book_id = ? ): 'N'
238 (The '\' characters won't actually appear in the output -- we are
239 using them as "line continuation markers" here.)
242 =head1 CONVERT TO A CHAINED ACTION
244 Although the example above uses the same C<Local> action type for the
245 method that we saw in the previous chapter of the tutorial, there is an
246 alternate approach that allows us to be more specific while also
247 paving the way for more advanced capabilities. Change the method
248 declaration for C<url_create> in C<lib/MyApp/Controller/Books.pm> you
249 entered above to match the following:
251 sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
252 # In addition to self & context, get the title, rating, &
253 # author_id args from the URL. Note that Catalyst automatically
254 # puts the first 3 arguments worth of extra information after the
255 # "/<controller_name>/<action_name/" into @_ because we specified
256 # "Args(3)". The args are separated by the '/' char on the URL.
257 my ($self, $c, $title, $rating, $author_id) = @_;
261 This converts the method to take advantage of the Chained
262 action/dispatch type. Chaining lets you have a single URL
263 automatically dispatch to several controller methods, each of which
264 can have precise control over the number of arguments that it will
265 receive. A chain can essentially be thought of having three parts --
266 a beginning, a middle, and an end. The bullets below summarize the key
267 points behind each of these parts of a chain:
281 B<Use "C<:Chained('/')>" to start a chain>
285 Get arguments through C<CaptureArgs()>
289 Specify the path to match with C<PathPart()>
302 Link to previous part of the chain with C<:Chained('_name_')>
306 Get arguments through C<CaptureArgs()>
310 Specify the path to match with C<PathPart()>
323 Link to previous part of the chain with C<:Chained('_name_')>
327 B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
331 Specify the path to match with C<PathPart()>
338 In our C<url_create> method above, we have combined all three parts into
339 a single method: C<:Chained('/')> to start the chain,
340 C<:PathPart('books/url_create')> to specify the base URL to match, and
341 C<:Args(3)> to capture exactly three arguments and to end the chain.
343 As we will see shortly, a chain can consist of as many "links" as you
344 wish, with each part capturing some arguments and doing some work
345 along the way. We will continue to use the Chained action type in this
346 chapter of the tutorial and explore slightly more advanced capabilities
347 with the base method and delete feature below. But Chained dispatch
348 is capable of far more. For additional information, see
349 L<Catalyst::Manual::Intro/Action types>,
350 L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained>,
351 and the 2006 Advent calendar entry on the subject:
352 L<http://www.catalystframework.org/calendar/2006/10>.
355 =head2 Try the Chained Action
357 If you look back at the development server startup logs from your
358 initial version of the C<url_create> method (the one using the
359 C<:Local> attribute), you will notice that it produced output similar
362 [debug] Loaded Path actions:
363 .-------------------------------------+--------------------------------------.
365 +-------------------------------------+--------------------------------------+
368 | /books | /books/index |
369 | /books/list | /books/list |
370 | /books/url_create | /books/url_create |
371 '-------------------------------------+--------------------------------------'
373 Now start the development server with our basic chained method in
374 place and the startup debug output should change to something along
375 the lines of the following:
377 [debug] Loaded Path actions:
378 .-------------------------------------+--------------------------------------.
380 +-------------------------------------+--------------------------------------+
383 | /books | /books/index |
384 | /books/list | /books/list |
385 '-------------------------------------+--------------------------------------'
387 [debug] Loaded Chained actions:
388 .-------------------------------------+--------------------------------------.
389 | Path Spec | Private |
390 +-------------------------------------+--------------------------------------+
391 | /books/url_create/*/*/* | /books/url_create |
392 '-------------------------------------+--------------------------------------'
394 C<url_create> has disappeared form the "Loaded Path actions" section
395 but it now shows up under the newly created "Loaded Chained actions"
396 section. And the "/*/*/*" portion clearly shows our requirement for
399 As with our non-chained version of C<url_create>, use your browser to
400 enter the following URL:
402 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
404 You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
405 'Stevens' with a rating of 5." along with a dump of the new book model
406 object. Click the "Return to list" link, and you should find that there
407 are now seven books shown (two copies of I<TCPIP_Illustrated_Vol-2>).
410 =head2 Refactor to Use a 'base' Method to Start the Chains
412 Let's make a quick update to our initial Chained action to show a
413 little more of the power of chaining. First, open
414 C<lib/MyApp/Controller/Books.pm> in your editor and add the following
419 Can place common logic to start chained dispatch here
423 sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
426 # Store the ResultSet in stash so it's available for other methods
427 $c->stash->{resultset} = $c->model('DB::Book');
429 # Print a message to the debug log
430 $c->log->debug('*** INSIDE BASE METHOD ***');
433 Here we print a log message and store the DBIC ResultSet in
434 C<$c-E<gt>stash-E<gt>{resultset}> so that it's automatically available
435 for other actions that chain off C<base>. If your controller always
436 needs a book ID as its first argument, you could have the base method
437 capture that argument (with C<:CaptureArgs(1)>) and use it to pull the
438 book object with C<-E<gt>find($id)> and leave it in the stash for
439 later parts of your chains to then act upon. Because we have several
440 actions that don't need to retrieve a book (such as the C<url_create>
441 we are working with now), we will instead add that functionality
442 to a common C<object> action shortly.
444 As for C<url_create>, let's modify it to first dispatch to C<base>.
445 Open up C<lib/MyApp/Controller/Books.pm> and edit the declaration for
446 C<url_create> to match the following:
448 sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
450 Next, try out the refactored chain by restarting the development
451 server. Notice that our "Loaded Chained actions" section has changed
454 [debug] Loaded Chained actions:
455 .-------------------------------------+--------------------------------------.
456 | Path Spec | Private |
457 +-------------------------------------+--------------------------------------+
458 | /books/url_create/*/*/* | /books/base (0) |
459 | | => /books/url_create |
460 '-------------------------------------+--------------------------------------'
462 The "Path Spec" is the same, but now it maps to two Private actions as
463 we would expect. The C<base> method is being triggered by the
464 C</books> part of the URL. However, the processing then continues to
465 the C<url_create> method because this method "chained" off C<base> and
466 specified C<:PathPart('url_create')> (note that we could have omitted
467 the "PathPart" here because it matches the name of the method, but we
468 will include it to make the logic behind the tutorial as explicit as
471 Once again, enter the following URL into your browser:
473 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
475 The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
476 rating of 5." message and a dump of the new book object should appear.
477 Also notice the extra "INSIDE BASE METHOD" debug message in the
478 development server output from the C<base> method. Click the "Return
479 to list" link, and you should find that there are now eight books
480 shown. (You may have a larger number of books if you repeated any of
481 the "create" actions more than once. Don't worry about it as long as
482 the number of books is appropriate for the number of times you added
483 new books... there should be the original five books added via
484 C<myapp01.sql> plus one additional book for each time you ran one
485 of the url_create variations above.)
488 =head1 MANUALLY BUILDING A CREATE FORM
490 Although the C<url_create> action in the previous step does begin to
491 reveal the power and flexibility of both Catalyst and DBIC, it's
492 obviously not a very realistic example of how users should be expected
493 to enter data. This section begins to address that concern.
496 =head2 Add Method to Display The Form
498 Edit C<lib/MyApp/Controller/Books.pm> and add the following method:
502 Display form to collect information for book to create
506 sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
509 # Set the TT template to use
510 $c->stash->{template} = 'books/form_create.tt2';
513 This action simply invokes a view containing a form to create a book.
516 =head2 Add a Template for the Form
518 Open C<root/src/books/form_create.tt2> in your editor and enter:
520 [% META title = 'Manual Form Book Create' -%]
522 <form method="post" action="[% c.uri_for('form_create_do') %]">
524 <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
525 <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
526 <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
528 <input type="submit" name="Submit" value="Submit">
531 Note that we have specified the target of the form data as
532 C<form_create_do>, the method created in the section that follows.
535 =head2 Add a Method to Process Form Values and Update Database
537 Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
538 save the form information to the database:
540 =head2 form_create_do
542 Take information from form and add to database
546 sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
549 # Retrieve the values from the form
550 my $title = $c->request->params->{title} || 'N/A';
551 my $rating = $c->request->params->{rating} || 'N/A';
552 my $author_id = $c->request->params->{author_id} || '1';
555 my $book = $c->model('DB::Book')->create({
559 # Handle relationship with author
560 $book->add_to_book_authors({author_id => $author_id});
561 # Note: Above is a shortcut for this:
562 # $book->create_related('book_authors', {author_id => $author_id});
564 # Store new model object in stash
565 $c->stash->{book} = $book;
567 # Avoid Data::Dumper issue mentioned earlier
568 # You can probably omit this
569 $Data::Dumper::Useperl = 1;
571 # Set the TT template to use
572 $c->stash->{template} = 'books/create_done.tt2';
576 =head2 Test Out The Form
578 If the application is still running from before, use C<Ctrl-C> to kill
579 it. Then restart the server:
581 $ script/myapp_server.pl
583 Notice that the server startup log reflects the two new chained
584 methods that we added:
586 [debug] Loaded Chained actions:
587 .-------------------------------------+--------------------------------------.
588 | Path Spec | Private |
589 +-------------------------------------+--------------------------------------+
590 | /books/form_create | /books/base (0) |
591 | | => /books/form_create |
592 | /books/form_create_do | /books/base (0) |
593 | | => /books/form_create_do |
594 | /books/url_create/*/*/* | /books/base (0) |
595 | | => /books/url_create |
596 '-------------------------------------+--------------------------------------'
598 Point your browser to L<http://localhost:3000/books/form_create> and
599 enter "TCP/IP Illustrated, Vol 3" for the title, a rating of 5, and an
600 author ID of 4. You should then see the output of the same
601 C<create_done.tt2> template seen in earlier examples. Finally, click
602 "Return to list" to view the full list of books.
604 B<Note:> Having the user enter the primary key ID for the author is
605 obviously crude; we will address this concern with a drop-down list and
606 add validation to our forms in Chapter 9.
609 =head1 A SIMPLE DELETE FEATURE
611 Turning our attention to the Delete portion of CRUD, this section
612 illustrates some basic techniques that can be used to remove information
616 =head2 Include a Delete Link in the List
618 Edit C<root/src/books/list.tt2> and update it to match the following (two
619 sections have changed: 1) the additional '<th>Links</th>' table header,
620 and 2) the four lines for the Delete link near the bottom):
622 [% # This is a TT comment. The '-' at the end "chomps" the newline. You won't -%]
623 [% # see this "chomping" in your browser because HTML ignores blank lines, but -%]
624 [% # it WILL eliminate a blank line if you view the HTML source. It's purely -%]
625 [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
627 [% # Provide a title -%]
628 [% META title = 'Book List' -%]
631 <tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
632 [% # Display each book in a table row %]
633 [% FOREACH book IN books -%]
635 <td>[% book.title %]</td>
636 <td>[% book.rating %]</td>
638 [% # NOTE: See "Exploring The Power of DBIC" for a better way to do this! -%]
639 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
640 [% # loop in 'side effect notation' to load just the last names of the -%]
641 [% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
642 [% # a value, so nothing will be printed here. But, if you have something -%]
643 [% # in TT that does return a value and you don't want it printed, you can -%]
644 [% # 1) assign it to a bogus value, or # 2) use the CALL keyword to -%]
645 [% # call it and discard the return value. -%]
647 tt_authors.push(author.last_name) FOREACH author = book.authors %]
648 [% # Now use a TT 'virtual method' to display the author count in parens -%]
649 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
650 ([% tt_authors.size | html %])
651 [% # Use another TT vmethod to join & print the names & comma separators -%]
652 [% tt_authors.join(', ') | html %]
655 [% # Add a link to delete a book %]
656 <a href="[% c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
662 The additional code is obviously designed to add a new column to the
663 right side of the table with a C<Delete> "button" (for simplicity, links
664 will be used instead of full HTML buttons; in practice, anything that
665 modifies data should be handled with a form sending a POST request).
667 Also notice that we are using a more advanced form of C<uri_for> than
668 we have seen before. Here we use
669 C<$c-E<gt>controller-E<gt>action_for> to automatically generate a URI
670 appropriate for that action based on the method we want to link to
671 while inserting the C<book.id> value into the appropriate place. Now,
672 if you ever change C<:PathPart('delete')> in your controller method to
673 C<:PathPart('kill')>, then your links will automatically update
674 without any changes to your .tt2 template file. As long as the name
675 of your method does not change (here, "delete"), then your links will
676 still be correct. There are a few shortcuts and options when using
683 If you are referring to a method in the current controller, you can
684 use C<$self-E<gt>action_for('_method_name_')>.
688 If you are referring to a method in a different controller, you need
689 to include that controller's name as an argument to C<controller()>, as in
690 C<$c-E<gt>controller('_controller_name_')-E<gt>action_for('_method_name_')>.
694 B<Note:> In practice you should B<never> use a GET request to delete a
695 record -- always use POST for actions that will modify data. We are
696 doing it here for illustrative and simplicity purposes only.
699 =head2 Add a Common Method to Retrieve a Book for the Chain
701 As mentioned earlier, since we have a mixture of actions that operate
702 on a single book ID and others that do not, we should not have C<base>
703 capture the book ID, find the corresponding book in the database and
704 save it in the stash for later links in the chain. However, just
705 because that logic does not belong in C<base> doesn't mean that we
706 can't create another location to centralize the book lookup code. In
707 our case, we will create a method called C<object> that will store the
708 specific book in the stash. Chains that always operate on a single
709 existing book can chain off this method, but methods such as
710 C<url_create> that don't operate on an existing book can chain
713 To add the C<object> method, edit C<lib/MyApp/Controller/Books.pm>
714 and add the following code:
718 Fetch the specified book object based on the book ID and store
723 sub object :Chained('base') :PathPart('id') :CaptureArgs(1) {
724 # $id = primary key of book to delete
725 my ($self, $c, $id) = @_;
727 # Find the book object and store it in the stash
728 $c->stash(object => $c->stash->{resultset}->find($id));
730 # Make sure the lookup was successful. You would probably
731 # want to do something like this in a real app:
732 # $c->detach('/error_404') if !$c->stash->{object};
733 die "Book $id not found!" if !$c->stash->{object};
735 # Print a message to the debug log
736 $c->log->debug("*** INSIDE OBJECT METHOD for obj id=$id ***");
739 Now, any other method that chains off C<object> will automatically
740 have the appropriate book waiting for it in
741 C<$c-E<gt>stash-E<gt>{object}>.
743 Also note that we are using a different technique for setting
744 C<$c-E<gt>stash>. The advantage of this style is that it lets you set
745 multiple stash variables at a time. For example:
747 $c->stash(object => $c->stash->{resultset}->find($id),
752 $c->stash({object => $c->stash->{resultset}->find($id),
753 another_thing => 1});
755 Either format works, but the C<$c-E<gt>stash(name =E<gt> value);>
756 style is growing in popularity -- you may wish to use it all
757 the time (even when you are only setting a single value).
760 =head2 Add a Delete Action to the Controller
762 Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
771 sub delete :Chained('object') :PathPart('delete') :Args(0) {
774 # Use the book object saved by 'object' and delete it along
775 # with related 'book_author' entries
776 $c->stash->{object}->delete;
778 # Set a status message to be displayed at the top of the view
779 $c->stash->{status_msg} = "Book deleted.";
781 # Forward to the list action/method in this controller
785 This method first deletes the book object saved by the C<object> method.
786 However, it also removes the corresponding entry from the
787 C<book_author> table with a cascading delete.
789 Then, rather than forwarding to a "delete done" page as we did with the
790 earlier create example, it simply sets the C<status_msg> to display a
791 notification to the user as the normal list view is rendered.
793 The C<delete> action uses the context C<forward> method to return the
794 user to the book list. The C<detach> method could have also been used.
795 Whereas C<forward> I<returns> to the original action once it is
796 completed, C<detach> does I<not> return. Other than that, the two are
800 =head2 Try the Delete Feature
802 If the application is still running from before, use C<Ctrl-C> to kill
803 it. Then restart the server:
805 $ DBIC_TRACE=1 script/myapp_server.pl
807 The C<delete> method now appears in the "Loaded Chained actions" section
808 of the startup debug output:
810 [debug] Loaded Chained actions:
811 .-------------------------------------+--------------------------------------.
812 | Path Spec | Private |
813 +-------------------------------------+--------------------------------------+
814 | /books/id/*/delete | /books/base (0) |
815 | | -> /books/object (1) |
816 | | => /books/delete |
817 | /books/form_create | /books/base (0) |
818 | | => /books/form_create |
819 | /books/form_create_do | /books/base (0) |
820 | | => /books/form_create_do |
821 | /books/url_create/*/*/* | /books/base (0) |
822 | | => /books/url_create |
823 '-------------------------------------+--------------------------------------'
825 Then point your browser to L<http://localhost:3000/books/list> and click
826 the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
827 "Book deleted" status message should display at the top of the page,
828 along with a list of the eight remaining books. You will also see the
829 cascading delete operation via the DBIC_TRACE output:
831 SELECT me.id, me.title, me.rating FROM book me WHERE ( ( me.id = ? ) ): '6'
832 DELETE FROM book WHERE ( id = ? ): '6'
833 SELECT me.book_id, me.author_id FROM book_author me WHERE ( me.book_id = ? ): '6'
834 DELETE FROM book_author WHERE ( author_id = ? AND book_id = ? ): '4', '6'
837 =head2 Fixing a Dangerous URL
839 Note the URL in your browser once you have performed the deletion in the
840 prior step -- it is still referencing the delete action:
842 http://localhost:3000/books/id/6/delete
844 What if the user were to press reload with this URL still active? In
845 this case the redundant delete is harmless (although it does generate
846 an exception screen, it doesn't perform any undesirable actions on the
847 application or database), but in other cases this could clearly be
850 We can improve the logic by converting to a redirect. Unlike
851 C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform
852 a server-side alteration in the flow of processing, a redirect is a
853 client-side mechanism that causes the browser to issue an entirely
854 new request. As a result, the URL in the browser is updated to match
855 the destination of the redirection URL.
857 To convert the forward used in the previous section to a redirect,
858 open C<lib/MyApp/Controller/Books.pm> and edit the existing
859 C<sub delete> method to match:
867 sub delete :Chained('object') :PathPart('delete') :Args(0) {
870 # Use the book object saved by 'object' and delete it along
871 # with related 'book_author' entries
872 $c->stash->{object}->delete;
874 # Set a status message to be displayed at the top of the view
875 $c->stash->{status_msg} = "Book deleted.";
877 # Redirect the user back to the list page. Note the use
878 # of $self->action_for as earlier in this section (BasicCRUD)
879 $c->response->redirect($c->uri_for($self->action_for('list')));
883 =head2 Try the Delete and Redirect Logic
885 Restart the development server and point your browser to
886 L<http://localhost:3000/books/list> (don't just hit "Refresh" in your
887 browser since we left the URL in an invalid state in the previous
888 section!) and delete the first copy of the remaining two
889 "TCPIP_Illustrated_Vol-2" books. The URL in your browser should return
890 to the L<http://localhost:3000/books/list> URL, so that is an
891 improvement, but notice that I<no green "Book deleted" status message is
892 displayed>. Because the stash is reset on every request (and a redirect
893 involves a second request), the C<status_msg> is cleared before it can
897 =head2 Using 'uri_for' to Pass Query Parameters
899 There are several ways to pass information across a redirect. One
900 option is to use the C<flash> technique that we will see in Chapter 5
901 of this tutorial; however, here we will pass the information via query
902 parameters on the redirect itself. Open
903 C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
904 method to match the following:
912 sub delete :Chained('object') :PathPart('delete') :Args(0) {
915 # Use the book object saved by 'object' and delete it along
916 # with related 'book_author' entries
917 $c->stash->{object}->delete;
919 # Redirect the user back to the list page with status msg as an arg
920 $c->response->redirect($c->uri_for($self->action_for('list'),
921 {status_msg => "Book deleted."}));
924 This modification simply leverages the ability of C<uri_for> to include
925 an arbitrary number of name/value pairs in a hash reference. Next, we
926 need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
931 [%# Status and error messages %]
932 <span class="message">[% status_msg || c.request.params.status_msg %]</span>
933 <span class="error">[% error_msg %]</span>
934 [%# This is where TT will stick all of your template's contents. -%]
936 </div><!-- end content -->
939 Although the sample above only shows the C<content> div, leave the
940 rest of the file intact -- the only change we made to the C<wrapper.tt2>
941 was to add "C<|| c.request.params.status_msg>" to the
942 C<E<lt>span class="message"E<gt>> line.
945 =head2 Try the Delete and Redirect With Query Param Logic
947 Restart the development server and point your browser to
948 L<http://localhost:3000/books/list> (you should now be able to safely
949 hit "refresh" in your browser). Then delete the remaining copy of
950 "TCPIP_Illustrated_Vol-2". The green "Book deleted" status message
953 B<NOTE:> Another popular method for maintaining server-side
954 information across a redirect is to use the C<flash> technique we
955 discuss in the next chapter of the tutorial,
956 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>. While
957 C<flash> is a "slicker" mechanism in that it's all handled by the
958 server and doesn't "pollute" your URLs, B<it is important to note that
959 C<flash> can lead to situations where the wrong information shows up
960 in the wrong browser window if the user has multiple windows or
961 browser tabs open>. For example, Window A causes something to be
962 placed in the stash, but before that window performs a redirect,
963 Window B makes a request to the server and gets the status information
964 that should really go to Window A. For this reason, you may wish
965 to use the "query param" technique shown here in your applications.
968 =head1 EXPLORING THE POWER OF DBIC
970 In this section we will explore some additional capabilities offered
971 by DBIx::Class. Although these features have relatively little to do
972 with Catalyst per se, you will almost certainly want to take advantage
973 of them in your applications.
976 =head2 Add Datetime Columns to Our Existing Books Table
978 Let's add two columns to our existing C<books> table to track when
979 each book was added and when each book is updated:
982 sqlite> ALTER TABLE book ADD created INTEGER;
983 sqlite> ALTER TABLE book ADD updated INTEGER;
984 sqlite> UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
985 sqlite> SELECT * FROM book;
986 1|CCSP SNRS Exam Certification Guide|5|2009-03-08 16:26:35|2009-03-08 16:26:35
987 2|TCP/IP Illustrated, Volume 1|5|2009-03-08 16:26:35|2009-03-08 16:26:35
988 3|Internetworking with TCP/IP Vol.1|4|2009-03-08 16:26:35|2009-03-08 16:26:35
989 4|Perl Cookbook|5|2009-03-08 16:26:35|2009-03-08 16:26:35
990 5|Designing with Web Standards|5|2009-03-08 16:26:35|2009-03-08 16:26:35
991 9|TCP/IP Illustrated, Vol 3|5|2009-03-08 16:26:35|2009-03-08 16:26:35
995 This will modify the C<books> table to include the two new fields
996 and populate those fields with the current time.
999 =head2 Update DBIx::Class to Automatically Handle the Datetime Columns
1001 Next, we should re-run the DBIC helper to update the Result Classes
1002 with the new fields:
1004 $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
1005 create=static components=TimeStamp dbi:SQLite:myapp.db
1006 exists "/root/dev/MyApp/script/../lib/MyApp/Model"
1007 exists "/root/dev/MyApp/script/../t"
1008 Dumping manual schema for MyApp::Schema to directory /root/dev/MyApp/script/../lib ...
1009 Schema dump completed.
1010 exists "/root/dev/MyApp/script/../lib/MyApp/Model/DB.pm"
1012 Notice that we modified our use of the helper slightly: we told
1013 it to include the L<DBIx::Class::TimeStamp|DBIx::Class::TimeStamp>
1014 in the C<load_components> line of the Result Classes.
1016 If you open C<lib/MyApp/Schema/Result/Book.pm> in your editor you
1017 should see that the C<created> and C<updated> fields are now included
1018 in the call to C<add_columns()>, but our relationship information below
1019 the "C<# DO NOT MODIFY...>" line was automatically preserved.
1021 While we have this file open, let's update it with some additional
1022 information to have DBIC automatically handle the updating of these
1023 two fields for us. Insert the following code at the bottom of the
1024 file (it B<must> be B<below> the "C<# DO NOT MODIFY...>" line and
1025 B<above> the C<1;> on the last line):
1028 # Enable automatic date handling
1030 __PACKAGE__->add_columns(
1032 { data_type => 'datetime', set_on_create => 1 },
1034 { data_type => 'datetime', set_on_create => 1, set_on_update => 1 },
1037 This will override the definition for these fields that Schema::Loader
1038 placed at the top of the file. The C<set_on_create> and
1039 C<set_on_update> options will cause DBIx::Class to automatically
1040 update the timestamps in these columns whenever a row is created or
1043 To test this out, restart the development server using the
1044 C<DBIC_TRACE=1> option:
1046 DBIC_TRACE=1 script/myapp_server.pl
1048 Then enter the following URL into your web browser:
1050 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
1052 You should get the same "Book Created" screen we saw above. However,
1053 if you now use the sqlite3 command-line tool to dump the C<books> table,
1054 you will see that the new book we added has an appropriate date and
1055 time entered for it (see the last line in the listing below):
1057 sqlite3 myapp.db "select * from book"
1058 1|CCSP SNRS Exam Certification Guide|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1059 2|TCP/IP Illustrated, Volume 1|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1060 3|Internetworking with TCP/IP Vol.1|4|2009-03-08 16:26:35|2009-03-08 16:26:35
1061 4|Perl Cookbook|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1062 5|Designing with Web Standards|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1063 9|TCP/IP Illustrated, Vol 3|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1064 10|TCPIP_Illustrated_Vol-2|5|2009-03-08 16:29:08|2009-03-08 16:29:08
1066 Notice in the debug log that the SQL DBIC generated has changed to
1067 incorporate the datetime logic:
1069 INSERT INTO book ( created, rating, title, updated ) VALUES ( ?, ?, ?, ? ):
1070 '2009-05-25 20:39:41', '5', 'TCPIP_Illustrated_Vol-2', '2009-05-25 20:39:41'
1071 INSERT INTO book_author ( author_id, book_id ) VALUES ( ?, ? ): '4', '10'
1074 =head2 Create a ResultSet Class
1076 An often overlooked but extremely powerful features of DBIC is that it
1077 allows you to supply your own subclasses of C<DBIx::Class::ResultSet>.
1078 It allows you to pull complex and unsightly "query code" out of your
1079 controllers and encapsulate it in a method of your ResultSet Class.
1080 These "canned queries" in your ResultSet Class can then be invoked
1081 via a single call, resulting in much cleaner and easier to read
1084 To illustrate the concept with a fairly simple example, let's create a
1085 method that returns books added in the last 10 minutes. Start by
1086 making a directory where DBIx::Class will look for our ResultSet Class:
1088 mkdir lib/MyApp/Schema/ResultSet
1090 Then open C<lib/MyApp/Schema/ResultSet/Book.pm> and enter the following:
1092 package MyApp::Schema::ResultSet::Book;
1096 use base 'DBIx::Class::ResultSet';
1098 =head2 created_after
1100 A predefined search for recently added books
1105 my ($self, $datetime) = @_;
1107 my $date_str = $self->_source_handle->schema->storage
1108 ->datetime_parser->format_datetime($datetime);
1110 return $self->search({
1111 created => { '>' => $date_str }
1117 Then we need to tell the Result Class to to treat this as a ResultSet
1118 Class. Open C<lib/MyApp/Schema/Result/Book.pm> and add the following
1119 above the "C<1;>" at the bottom of the file:
1122 # Set ResultSet Class
1124 __PACKAGE__->resultset_class('MyApp::Schema::ResultSet::Book');
1126 Then add the following method to the C<lib/MyApp/Controller/Books.pm>:
1130 List recently created books
1134 sub list_recent :Chained('base') :PathPart('list_recent') :Args(1) {
1135 my ($self, $c, $mins) = @_;
1137 # Retrieve all of the book records as book model objects and store in the
1138 # stash where they can be accessed by the TT template, but only
1139 # retrieve books created within the last $min number of minutes
1140 $c->stash->{books} = [$c->model('DB::Book')
1141 ->created_after(DateTime->now->subtract(minutes => $mins))];
1143 # Set the TT template to use. You will almost always want to do this
1144 # in your action methods (action methods respond to user input in
1145 # your controllers).
1146 $c->stash->{template} = 'books/list.tt2';
1149 Now start the development server with C<DBIC_TRACE=1> and try
1150 different values for the minutes argument (the final number value) for
1151 the URL C<http://localhost:3000/books/list_recent/10>. For example,
1152 this would list all books added in the last fifteen minutes:
1154 http://localhost:3000/books/list_recent/15
1156 Depending on how recently you added books, you might want to
1157 try a higher or lower value.
1160 =head2 Chaining ResultSets
1162 One of the most helpful and powerful features in DBIx::Class is that
1163 it allows you to "chain together" a series of queries (note that this
1164 has nothing to do with the "Chained Dispatch" for Catalyst that we
1165 were discussing above). Because each ResultSet returns another
1166 ResultSet, you can take an initial query and immediately feed that
1167 into a second query (and so on for as many queries you need). Note
1168 that no matter how many ResultSets you chain together, the database
1169 itself will not be hit until you use a method that attempts to access
1170 the data. And, because this technique carries over to the ResultSet
1171 Class feature we implemented in the previous section for our "canned
1172 search", we can combine the two capabilities. For example, let's add
1173 an action to our C<Books> controller that lists books that are both
1174 recent I<and> have "TCP" in the title. Open up
1175 C<lib/MyApp/Controller/Books.pm> and add the following method:
1177 =head2 list_recent_tcp
1179 List recently created books
1183 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1184 my ($self, $c, $mins) = @_;
1186 # Retrieve all of the book records as book model objects and store in the
1187 # stash where they can be accessed by the TT template, but only
1188 # retrieve books created within the last $min number of minutes
1189 # AND that have 'TCP' in the title
1190 $c->stash->{books} = [$c->model('DB::Book')
1191 ->created_after(DateTime->now->subtract(minutes => $mins))
1192 ->search({title => {'like', '%TCP%'}})
1195 # Set the TT template to use. You will almost always want to do this
1196 # in your action methods (action methods respond to user input in
1197 # your controllers).
1198 $c->stash->{template} = 'books/list.tt2';
1201 To try this out, restart the development server with:
1203 DBIC_TRACE=1 script/myapp_server.pl
1205 And enter the following URL into your browser:
1207 http://localhost:3000/books/list_recent_tcp/100
1209 And you should get a list of books added in the last 100 minutes that
1210 contain the string "TCP" in the title. However, if you look at all
1211 books within the last 100 minutes, you should get a longer list
1212 (again, you might have to adjust the number of minutes depending on
1213 how recently you added books to your database):
1215 http://localhost:3000/books/list_recent/100
1217 Take a look at the DBIC_TRACE output in the development server log for
1218 the first URL and you should see something similar to the following:
1220 SELECT me.id, me.title, me.rating, me.created, me.updated FROM book me
1221 WHERE ( ( title LIKE ? AND created > ? ) ): '%TCP%', '2009-05-25 19:09:13'
1223 However, let's not pollute our controller code with this raw "TCP"
1224 query -- it would be cleaner to encapsulate that code in a method on
1225 our ResultSet Class. To do this, open
1226 C<lib/MyApp/Schema/ResultSet/Book.pm> and add the following method:
1230 A predefined search for books with a 'LIKE' search in the string
1235 my ($self, $title_str) = @_;
1237 return $self->search({
1238 title => { 'like' => "%$title_str%" }
1242 We defined the search string as C<$title_str> to make the method more
1243 flexible. Now update the C<list_recent_tcp> method in
1244 C<lib/MyApp/Controller/Books.pm> to match the following (we have
1245 replaced the C<-E<gt>search> line with the C<-E<gt>title_like> line
1246 shown here -- the rest of the method should be the same):
1248 =head2 list_recent_tcp
1250 List recently created books
1254 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1255 my ($self, $c, $mins) = @_;
1257 # Retrieve all of the book records as book model objects and store in the
1258 # stash where they can be accessed by the TT template, but only
1259 # retrieve books created within the last $min number of minutes
1260 # AND that have 'TCP' in the title
1261 $c->stash->{books} = [$c->model('DB::Book')
1262 ->created_after(DateTime->now->subtract(minutes => $mins))
1266 # Set the TT template to use. You will almost always want to do this
1267 # in your action methods (action methods respond to user input in
1268 # your controllers).
1269 $c->stash->{template} = 'books/list.tt2';
1272 Then restart the development server and try out the C<list_recent_tcp>
1273 and C<list_recent> URL as we did above. It should work just the same,
1274 but our code is obviously cleaner and more modular, while also being
1275 more flexible at the same time.
1278 =head2 Adding Methods to Result Classes
1280 In the previous two sections we saw a good example of how we could use
1281 DBIx::Class ResultSet Classes to clean up our code for an entire query
1282 (for example, our "canned searches" that filtered the entire query).
1283 We can do a similar improvement when working with individual rows as
1284 well. Whereas the ResultSet construct is used in DBIC to correspond
1285 to an entire query, the Result Class construct is used to represent a
1286 row. Therefore, we can add row-specific "helper methods" to our Result
1287 Classes stored in C<lib/MyApp/Schema/Result/>. For example, open
1288 C<lib/MyApp/Schema/Result/Author.pm> and add the following method (as
1289 always, it must be above the closing "C<1;>"):
1297 return $self->first_name . ' ' . $self->last_name;
1300 This will allow us to conveniently retrieve both the first and last
1301 name for an author in one shot. Now open C<root/src/books/list.tt2>
1302 and change the definition of C<tt_authors> from this:
1305 [% tt_authors = [ ];
1306 tt_authors.push(author.last_name) FOREACH author = book.authors %]
1312 [% tt_authors = [ ];
1313 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1316 (Only C<author.last_name> was changed to C<author.full_name> -- the
1317 rest of the file should remain the same.)
1319 Now restart the development server and go to the standard book list
1322 http://localhost:3000/books/list
1324 The "Author(s)" column will now contain both the first and last name.
1325 And, because the concatenation logic was encapsulated inside our
1326 Result Class, it keeps the code inside our .tt template nice and clean
1327 (remember, we want the templates to be as close to pure HTML markup as
1328 possible). Obviously, this capability becomes even more useful as you
1329 use to to remove even more complicated row-specific logic from your
1333 =head2 Moving Complicated View Code to the Model
1335 The previous section illustrated how we could use a Result Class
1336 method to print the full names of the authors without adding any extra
1337 code to our view, but it still left us with a fairly ugly mess (see
1338 C<root/src/books/list.tt2>):
1342 [% # NOTE: See Chapter 4 for a better way to do this! -%]
1343 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
1344 [% # loop in 'side effect notation' to load just the last names of the -%]
1345 [% # authors into the list. Note that the 'push' TT vmethod does not print -%]
1346 [% # a value, so nothing will be printed here. But, if you have something -%]
1347 [% # in TT that does return a method and you don't want it printed, you -%]
1348 [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to -%]
1349 [% # call it and discard the return value. -%]
1350 [% tt_authors = [ ];
1351 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1352 [% # Now use a TT 'virtual method' to display the author count in parens -%]
1353 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
1354 ([% tt_authors.size | html %])
1355 [% # Use another TT vmethod to join & print the names & comma separators -%]
1356 [% tt_authors.join(', ') | html %]
1360 Let's combine some of the techniques used earlier in this section to
1361 clean this up. First, let's add a method to our Book Result Class to
1362 return the number of authors for a book. Open
1363 C<lib/MyApp/Schema/Result/Book.pm> and add the following method:
1367 Return the number of authors for the current book
1374 # Use the 'many_to_many' relationship to fetch all of the authors for the current
1375 # and the 'count' method in DBIx::Class::ResultSet to get a SQL COUNT
1376 return $self->authors->count;
1379 Next, let's add a method to return a list of authors for a book to the
1380 same C<lib/MyApp/Schema/Result/Book.pm> file:
1384 Return a comma-separated list of authors for the current book
1391 # Loop through all authors for the current book, calling all the 'full_name'
1392 # Result Class method for each
1394 foreach my $author ($self->authors) {
1395 push(@names, $author->full_name);
1398 return join(', ', @names);
1401 This method loops through each author, using the C<full_name> Result
1402 Class method we added to C<lib/MyApp/Schema/Result/Author.pm> in the
1405 Using these two methods, we can simplify our TT code. Open
1406 C<root/src/books/list.tt2> and update the "Author(s)" table cell to
1407 match the following:
1411 [% # Print count and author list using Result Class methods -%]
1412 ([% book.author_count | html %]) [% book.author_list | html %]
1416 Although most of the code we removed comprised comments, the overall
1417 effect is dramatic... because our view code is so simple, we don't
1418 huge comments to clue people in to the gist of our code. The view
1419 code is now self-documenting and readable enough that you could
1420 probably get by with no comments at all. All of the "complex" work is
1421 being done in our Result Class methods (and, because we have broken
1422 the code into nice, modular chucks, the Result Class code is hardly
1423 something you would call complex).
1425 As we saw in this section, always strive to keep your view AND
1426 controller code as simple as possible by pulling code out into your
1427 model objects. Because DBIx::Class can be easily extended in so many
1428 ways, it's an excellent to way accomplish this objective. It will
1429 make your code cleaner, easier to write, less error-prone, and easier
1430 to debug and maintain.
1435 Kennedy Clark, C<hkclark@gmail.com>
1437 Please report any errors, issues or suggestions to the author. The
1438 most recent version of the Catalyst Tutorial can be found at
1439 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.
1441 Copyright 2006-2008, Kennedy Clark, under Creative Commons License
1442 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).