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<Catalyst::Plugin::AutoCRUD|Catalyst::Plugin::AutoCRUD>,
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 3.5+ years old). If you are following
187 along in Debian, then you should be on at least v2.20. You can test
188 your version of Template Toolkit with the following:
190 perl -MTemplate -e 'print "$Template::VERSION\n"'
193 =head2 Try the 'url_create' Feature
195 If the application is still running from before, use C<Ctrl-C> to kill
196 it. Then restart the server:
198 $ DBIC_TRACE=1 script/myapp_server.pl
200 Note that new path for C</books/url_create> appears in the startup debug
203 B<TIP>: You can use C<script/myapp_server.pl -r> to have the development
204 server auto-detect changed files and reload itself (if your browser acts
205 odd, you should also try throwing in a C<-k>). If you make changes to
206 the TT templates only, you do not need to reload the development server
207 (only changes to "compiled code" such as Controller and Model C<.pm>
208 files require a reload).
210 Next, use your browser to enter the following URL:
212 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
214 Your browser should display "Added book 'TCPIP_Illustrated_Vol-2' by
215 'Stevens' with a rating of 5." along with a dump of the new book model
216 object as it was returned by DBIC. You should also see the following
217 DBIC debug messages displayed in the development server log messages
218 if you have DBIC_TRACE set:
220 INSERT INTO book (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
221 INSERT INTO book_author (author_id, book_id) VALUES (?, ?): `4', `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). You should now
230 see the six DBIC debug messages similar to the following (where
233 SELECT author.id, author.first_name, author.last_name
234 FROM book_author me JOIN author author
235 ON author.id = me.author_id WHERE ( me.book_id = ? ): 'N'
238 =head1 CONVERT TO A CHAINED ACTION
240 Although the example above uses the same C<Local> action type for the
241 method that we saw in the previous chapter of the tutorial, there is an
242 alternate approach that allows us to be more specific while also
243 paving the way for more advanced capabilities. Change the method
244 declaration for C<url_create> in C<lib/MyApp/Controller/Books.pm> you
245 entered above to match the following:
247 sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
248 # In addition to self & context, get the title, rating, &
249 # author_id args from the URL. Note that Catalyst automatically
250 # puts the first 3 arguments worth of extra information after the
251 # "/<controller_name>/<action_name/" into @_ because we specified
252 # "Args(3)". The args are separated by the '/' char on the URL.
253 my ($self, $c, $title, $rating, $author_id) = @_;
257 This converts the method to take advantage of the Chained
258 action/dispatch type. Chaining lets you have a single URL
259 automatically dispatch to several controller methods, each of which
260 can have precise control over the number of arguments that it will
261 receive. A chain can essentially be thought of having three parts --
262 a beginning, a middle, and an end. The bullets below summarize the key
263 points behind each of these parts of a chain:
277 B<Use "C<:Chained('/')>" to start a chain>
281 Get arguments through C<CaptureArgs()>
285 Specify the path to match with C<PathPart()>
298 Link to previous part of the chain with C<:Chained('_name_')>
302 Get arguments through C<CaptureArgs()>
306 Specify the path to match with C<PathPart()>
319 Link to previous part of the chain with C<:Chained('_name_')>
323 B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
327 Specify the path to match with C<PathPart()>
334 In our C<url_create> method above, we have combined all three parts into
335 a single method: C<:Chained('/')> to start the chain,
336 C<:PathPart('books/url_create')> to specify the base URL to match, and
337 C<:Args(3)> to capture exactly three arguments and to end the chain.
339 As we will see shortly, a chain can consist of as many "links" as you
340 wish, with each part capturing some arguments and doing some work
341 along the way. We will continue to use the Chained action type in this
342 chapter of the tutorial and explore slightly more advanced capabilities
343 with the base method and delete feature below. But Chained dispatch
344 is capable of far more. For additional information, see
345 L<Catalyst::Manual::Intro/Action types>,
346 L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained>,
347 and the 2006 Advent calendar entry on the subject:
348 L<http://www.catalystframework.org/calendar/2006/10>.
351 =head2 Try the Chained Action
353 If you look back at the development server startup logs from your
354 initial version of the C<url_create> method (the one using the
355 C<:Local> attribute), you will notice that it produced output similar
358 [debug] Loaded Path actions:
359 .-------------------------------------+--------------------------------------.
361 +-------------------------------------+--------------------------------------+
364 | /books | /books/index |
365 | /books/list | /books/list |
366 | /books/url_create | /books/url_create |
367 '-------------------------------------+--------------------------------------'
369 Now start the development server with our basic chained method in
370 place and the startup debug output should change to something along
371 the lines of the following:
373 [debug] Loaded Path actions:
374 .-------------------------------------+--------------------------------------.
376 +-------------------------------------+--------------------------------------+
379 | /books | /books/index |
380 | /books/list | /books/list |
381 '-------------------------------------+--------------------------------------'
383 [debug] Loaded Chained actions:
384 .-------------------------------------+--------------------------------------.
385 | Path Spec | Private |
386 +-------------------------------------+--------------------------------------+
387 | /books/url_create/*/*/* | /books/url_create |
388 '-------------------------------------+--------------------------------------'
390 C<url_create> has disappeared form the "Loaded Path actions" section
391 but it now shows up under the newly created "Loaded Chained actions"
392 section. And the "/*/*/*" portion clearly shows our requirement for
395 As with our non-chained version of C<url_create>, use your browser to
396 enter the following URL:
398 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
400 You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
401 'Stevens' with a rating of 5." along with a dump of the new book model
402 object. Click the "Return to list" link, and you should find that there
403 are now seven books shown (two copies of I<TCPIP_Illustrated_Vol-2>).
406 =head2 Refactor to Use a 'base' Method to Start the Chains
408 Let's make a quick update to our initial Chained action to show a
409 little more of the power of chaining. First, open
410 C<lib/MyApp/Controller/Books.pm> in your editor and add the following
415 Can place common logic to start chained dispatch here
419 sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
422 # Store the ResultSet in stash so it's available for other methods
423 $c->stash->{resultset} = $c->model('DB::Book');
425 # Print a message to the debug log
426 $c->log->debug('*** INSIDE BASE METHOD ***');
429 Here we print a log message and store the DBIC ResultSet in
430 C<$c-E<gt>stash-E<gt>{resultset}> so that it's automatically available
431 for other actions that chain off C<base>. If your controller always
432 needs a book ID as its first argument, you could have the base method
433 capture that argument (with C<:CaptureArgs(1)>) and use it to pull the
434 book object with C<-E<gt>find($id)> and leave it in the stash for
435 later parts of your chains to then act upon. Because we have several
436 actions that don't need to retrieve a book (such as the C<url_create>
437 we are working with now), we will instead add that functionality
438 to a common C<object> action shortly.
440 As for C<url_create>, let's modify it to first dispatch to C<base>.
441 Open up C<lib/MyApp/Controller/Books.pm> and edit the declaration for
442 C<url_create> to match the following:
444 sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
446 Next, try out the refactored chain by restarting the development
447 server. Notice that our "Loaded Chained actions" section has changed
450 [debug] Loaded Chained actions:
451 .-------------------------------------+--------------------------------------.
452 | Path Spec | Private |
453 +-------------------------------------+--------------------------------------+
454 | /books/url_create/*/*/* | /books/base (0) |
455 | | => /books/url_create |
456 '-------------------------------------+--------------------------------------'
458 The "Path Spec" is the same, but now it maps to two Private actions as
459 we would expect. The C<base> method is being triggered by the
460 C</books> part of the URL. However, the processing then continues to
461 the C<url_create> method because this method "chained" off C<base> and
462 specified C<:PathPart('url_create')> (note that we could have omitted
463 the "PathPart" here because it matches the name of the method, but we
464 will include it to make the logic as explicit as possible).
466 Once again, enter the following URL into your browser:
468 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
470 The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
471 rating of 5." message and a dump of the new book object should appear.
472 Also notice the extra "INSIDE BASE METHOD" debug message in the
473 development server output from the C<base> method. Click the "Return
474 to list" link, and you should find that there are now eight books
475 shown. (You may have a larger number of books if you repeated any of
476 the "create" actions more than once. Don't worry about it as long as
477 the number of books is appropriate for the number of times you added
478 new books... there should be the original five books added via
479 C<myapp01.sql> plus one additional book for each time you ran one
480 of the url_create variations above.)
483 =head1 MANUALLY BUILDING A CREATE FORM
485 Although the C<url_create> action in the previous step does begin to
486 reveal the power and flexibility of both Catalyst and DBIC, it's
487 obviously not a very realistic example of how users should be expected
488 to enter data. This section begins to address that concern.
491 =head2 Add Method to Display The Form
493 Edit C<lib/MyApp/Controller/Books.pm> and add the following method:
497 Display form to collect information for book to create
501 sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
504 # Set the TT template to use
505 $c->stash->{template} = 'books/form_create.tt2';
508 This action simply invokes a view containing a form to create a book.
511 =head2 Add a Template for the Form
513 Open C<root/src/books/form_create.tt2> in your editor and enter:
515 [% META title = 'Manual Form Book Create' -%]
517 <form method="post" action="[% c.uri_for('form_create_do') %]">
519 <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
520 <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
521 <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
523 <input type="submit" name="Submit" value="Submit">
526 Note that we have specified the target of the form data as
527 C<form_create_do>, the method created in the section that follows.
530 =head2 Add a Method to Process Form Values and Update Database
532 Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
533 save the form information to the database:
535 =head2 form_create_do
537 Take information from form and add to database
541 sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
544 # Retrieve the values from the form
545 my $title = $c->request->params->{title} || 'N/A';
546 my $rating = $c->request->params->{rating} || 'N/A';
547 my $author_id = $c->request->params->{author_id} || '1';
550 my $book = $c->model('DB::Book')->create({
554 # Handle relationship with author
555 $book->add_to_book_authors({author_id => $author_id});
556 # Note: Above is a shortcut for this:
557 # $book->create_related('book_authors', {author_id => $author_id});
559 # Store new model object in stash
560 $c->stash->{book} = $book;
562 # Avoid Data::Dumper issue mentioned earlier
563 # You can probably omit this
564 $Data::Dumper::Useperl = 1;
566 # Set the TT template to use
567 $c->stash->{template} = 'books/create_done.tt2';
571 =head2 Test Out The Form
573 If the application is still running from before, use C<Ctrl-C> to kill
574 it. Then restart the server:
576 $ script/myapp_server.pl
578 Notice that the server startup log reflects the two new chained
579 methods that we added:
581 [debug] Loaded Chained actions:
582 .-------------------------------------+--------------------------------------.
583 | Path Spec | Private |
584 +-------------------------------------+--------------------------------------+
585 | /books/form_create | /books/base (0) |
586 | | => /books/form_create |
587 | /books/form_create_do | /books/base (0) |
588 | | => /books/form_create_do |
589 | /books/url_create/*/*/* | /books/base (0) |
590 | | => /books/url_create |
591 '-------------------------------------+--------------------------------------'
593 Point your browser to L<http://localhost:3000/books/form_create> and
594 enter "TCP/IP Illustrated, Vol 3" for the title, a rating of 5, and an
595 author ID of 4. You should then see the output of the same
596 C<create_done.tt2> template seen in earlier examples. Finally, click
597 "Return to list" to view the full list of books.
599 B<Note:> Having the user enter the primary key ID for the author is
600 obviously crude; we will address this concern with a drop-down list and
601 add validation to our forms in Chapter 9.
604 =head1 A SIMPLE DELETE FEATURE
606 Turning our attention to the Delete portion of CRUD, this section
607 illustrates some basic techniques that can be used to remove information
611 =head2 Include a Delete Link in the List
613 Edit C<root/src/books/list.tt2> and update it to match the following (two
614 sections have changed: 1) the additional '<th>Links</th>' table header,
615 and 2) the four lines for the Delete link near the bottom):
617 [% # This is a TT comment. The '-' at the end "chomps" the newline. You won't -%]
618 [% # see this "chomping" in your browser because HTML ignores blank lines, but -%]
619 [% # it WILL eliminate a blank line if you view the HTML source. It's purely -%]
620 [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
622 [% # Provide a title -%]
623 [% META title = 'Book List' -%]
626 <tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
627 [% # Display each book in a table row %]
628 [% FOREACH book IN books -%]
630 <td>[% book.title %]</td>
631 <td>[% book.rating %]</td>
633 [% # NOTE: See "Exploring The Power of DBIC" for a better way to do this! -%]
634 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
635 [% # loop in 'side effect notation' to load just the last names of the -%]
636 [% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
637 [% # a value, so nothing will be printed here. But, if you have something -%]
638 [% # in TT that does return a value and you don't want it printed, you can -%]
639 [% # 1) assign it to a bogus value, or -%]
640 [% # 2) use the CALL keyword to call it and discard the return value. -%]
642 tt_authors.push(author.last_name) FOREACH author = book.authors %]
643 [% # Now use a TT 'virtual method' to display the author count in parens -%]
644 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
645 ([% tt_authors.size | html %])
646 [% # Use another TT vmethod to join & print the names & comma separators -%]
647 [% tt_authors.join(', ') | html %]
650 [% # Add a link to delete a book %]
651 <a href="[% c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
657 The additional code is obviously designed to add a new column to the
658 right side of the table with a C<Delete> "button" (for simplicity, links
659 will be used instead of full HTML buttons; in practice, anything that
660 modifies data should be handled with a form sending a POST request).
662 Also notice that we are using a more advanced form of C<uri_for> than
663 we have seen before. Here we use
664 C<$c-E<gt>controller-E<gt>action_for> to automatically generate a URI
665 appropriate for that action based on the method we want to link to
666 while inserting the C<book.id> value into the appropriate place. Now,
667 if you ever change C<:PathPart('delete')> in your controller method to
668 C<:PathPart('kill')>, then your links will automatically update
669 without any changes to your .tt2 template file. As long as the name
670 of your method does not change (here, "delete"), then your links will
671 still be correct. There are a few shortcuts and options when using
678 If you are referring to a method in the current controller, you can
679 use C<$self-E<gt>action_for('_method_name_')>.
683 If you are referring to a method in a different controller, you need
684 to include that controller's name as an argument to C<controller()>, as in
685 C<$c-E<gt>controller('_controller_name_')-E<gt>action_for('_method_name_')>.
689 B<Note:> In practice you should B<never> use a GET request to delete a
690 record -- always use POST for actions that will modify data. We are
691 doing it here for illustrative and simplicity purposes only.
694 =head2 Add a Common Method to Retrieve a Book for the Chain
696 As mentioned earlier, since we have a mixture of actions that operate
697 on a single book ID and others that do not, we should not have C<base>
698 capture the book ID, find the corresponding book in the database and
699 save it in the stash for later links in the chain. However, just
700 because that logic does not belong in C<base> doesn't mean that we
701 can't create another location to centralize the book lookup code. In
702 our case, we will create a method called C<object> that will store the
703 specific book in the stash. Chains that always operate on a single
704 existing book can chain off this method, but methods such as
705 C<url_create> that don't operate on an existing book can chain
708 To add the C<object> method, edit C<lib/MyApp/Controller/Books.pm>
709 and add the following code:
713 Fetch the specified book object based on the book ID and store
718 sub object :Chained('base') :PathPart('id') :CaptureArgs(1) {
719 # $id = primary key of book to delete
720 my ($self, $c, $id) = @_;
722 # Find the book object and store it in the stash
723 $c->stash(object => $c->stash->{resultset}->find($id));
725 # Make sure the lookup was successful. You would probably
726 # want to do something like this in a real app:
727 # $c->detach('/error_404') if !$c->stash->{object};
728 die "Book $id not found!" if !$c->stash->{object};
730 # Print a message to the debug log
731 $c->log->debug("*** INSIDE OBJECT METHOD for obj id=$id ***");
734 Now, any other method that chains off C<object> will automatically
735 have the appropriate book waiting for it in
736 C<$c-E<gt>stash-E<gt>{object}>.
738 Also note that we are using a different technique for setting
739 C<$c-E<gt>stash>. The advantage of this style is that it lets you set
740 multiple stash variables at a time. For example:
742 $c->stash(object => $c->stash->{resultset}->find($id),
747 $c->stash({object => $c->stash->{resultset}->find($id),
748 another_thing => 1});
750 Either format works, but the C<$c-E<gt>stash(name =E<gt> value);>
751 style is growing in popularity -- you may wish to use it all
752 the time (even when you are only setting a single value).
755 =head2 Add a Delete Action to the Controller
757 Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
766 sub delete :Chained('object') :PathPart('delete') :Args(0) {
769 # Use the book object saved by 'object' and delete it along
770 # with related 'book_author' entries
771 $c->stash->{object}->delete;
773 # Set a status message to be displayed at the top of the view
774 $c->stash->{status_msg} = "Book deleted.";
776 # Forward to the list action/method in this controller
780 This method first deletes the book object saved by the C<object> method.
781 However, it also removes the corresponding entry from the
782 C<book_author> table with a cascading delete.
784 Then, rather than forwarding to a "delete done" page as we did with the
785 earlier create example, it simply sets the C<status_msg> to display a
786 notification to the user as the normal list view is rendered.
788 The C<delete> action uses the context C<forward> method to return the
789 user to the book list. The C<detach> method could have also been used.
790 Whereas C<forward> I<returns> to the original action once it is
791 completed, C<detach> does I<not> return. Other than that, the two are
795 =head2 Try the Delete Feature
797 If the application is still running from before, use C<Ctrl-C> to kill
798 it. Then restart the server:
800 $ DBIC_TRACE=1 script/myapp_server.pl
802 The C<delete> method now appears in the "Loaded Chained actions" section
803 of the startup debug output:
805 [debug] Loaded Chained actions:
806 .-------------------------------------+--------------------------------------.
807 | Path Spec | Private |
808 +-------------------------------------+--------------------------------------+
809 | /books/id/*/delete | /books/base (0) |
810 | | -> /books/object (1) |
811 | | => /books/delete |
812 | /books/form_create | /books/base (0) |
813 | | => /books/form_create |
814 | /books/form_create_do | /books/base (0) |
815 | | => /books/form_create_do |
816 | /books/url_create/*/*/* | /books/base (0) |
817 | | => /books/url_create |
818 '-------------------------------------+--------------------------------------'
820 Then point your browser to L<http://localhost:3000/books/list> and click
821 the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
822 "Book deleted" status message should display at the top of the page,
823 along with a list of the eight remaining books. You will also see the
824 cascading delete operation via the DBIC_TRACE output:
826 SELECT me.id, me.title, me.rating FROM book me WHERE ( ( me.id = ? ) ): '6'
827 DELETE FROM book WHERE ( id = ? ): '6'
828 SELECT me.book_id, me.author_id FROM book_author me WHERE ( me.book_id = ? ): '6'
829 DELETE FROM book_author WHERE ( author_id = ? AND book_id = ? ): '4', '6'
832 =head2 Fixing a Dangerous URL
834 Note the URL in your browser once you have performed the deletion in the
835 prior step -- it is still referencing the delete action:
837 http://localhost:3000/books/id/6/delete
839 What if the user were to press reload with this URL still active? In
840 this case the redundant delete is harmless (although it does generate
841 an exception screen, it doesn't perform any undesirable actions on the
842 application or database), but in other cases this could clearly be
845 We can improve the logic by converting to a redirect. Unlike
846 C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform
847 a server-side alteration in the flow of processing, a redirect is a
848 client-side mechanism that causes the browser to issue an entirely
849 new request. As a result, the URL in the browser is updated to match
850 the destination of the redirection URL.
852 To convert the forward used in the previous section to a redirect,
853 open C<lib/MyApp/Controller/Books.pm> and edit the existing
854 C<sub delete> method to match:
862 sub delete :Chained('object') :PathPart('delete') :Args(0) {
865 # Use the book object saved by 'object' and delete it along
866 # with related 'book_author' entries
867 $c->stash->{object}->delete;
869 # Set a status message to be displayed at the top of the view
870 $c->stash->{status_msg} = "Book deleted.";
872 # Redirect the user back to the list page. Note the use
873 # of $self->action_for as earlier in this section (BasicCRUD)
874 $c->response->redirect($c->uri_for($self->action_for('list')));
878 =head2 Try the Delete and Redirect Logic
880 Restart the development server and point your browser to
881 L<http://localhost:3000/books/list> (don't just hit "Refresh" in your
882 browser since we left the URL in an invalid state in the previous
883 section!) and delete the first copy of the remaining two
884 "TCPIP_Illustrated_Vol-2" books. The URL in your browser should return
885 to the L<http://localhost:3000/books/list> URL, so that is an
886 improvement, but notice that I<no green "Book deleted" status message is
887 displayed>. Because the stash is reset on every request (and a redirect
888 involves a second request), the C<status_msg> is cleared before it can
892 =head2 Using 'uri_for' to Pass Query Parameters
894 There are several ways to pass information across a redirect. One
895 option is to use the C<flash> technique that we will see in Chapter 5
896 of this tutorial; however, here we will pass the information via query
897 parameters on the redirect itself. Open
898 C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
899 method to match the following:
907 sub delete :Chained('object') :PathPart('delete') :Args(0) {
910 # Use the book object saved by 'object' and delete it along
911 # with related 'book_author' entries
912 $c->stash->{object}->delete;
914 # Redirect the user back to the list page with status msg as an arg
915 $c->response->redirect($c->uri_for($self->action_for('list'),
916 {status_msg => "Book deleted."}));
919 This modification simply leverages the ability of C<uri_for> to include
920 an arbitrary number of name/value pairs in a hash reference. Next, we
921 need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
926 [%# Status and error messages %]
927 <span class="message">[% status_msg || c.request.params.status_msg %]</span>
928 <span class="error">[% error_msg %]</span>
929 [%# This is where TT will stick all of your template's contents. -%]
931 </div><!-- end content -->
934 Although the sample above only shows the C<content> div, leave the
935 rest of the file intact -- the only change we made to the C<wrapper.tt2>
936 was to add "C<|| c.request.params.status_msg>" to the
937 C<E<lt>span class="message"E<gt>> line.
940 =head2 Try the Delete and Redirect With Query Param Logic
942 Restart the development server and point your browser to
943 L<http://localhost:3000/books/list> (you should now be able to safely
944 hit "refresh" in your browser). Then delete the remaining copy of
945 "TCPIP_Illustrated_Vol-2". The green "Book deleted" status message
948 B<NOTE:> Another popular method for maintaining server-side
949 information across a redirect is to use the C<flash> technique we
950 discuss in the next chapter of the tutorial,
951 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>. While
952 C<flash> is a "slicker" mechanism in that it's all handled by the
953 server and doesn't "pollute" your URLs, B<it is important to note that
954 C<flash> can lead to situations where the wrong information shows up
955 in the wrong browser window if the user has multiple windows or
956 browser tabs open>. For example, Window A causes something to be
957 placed in the stash, but before that window performs a redirect,
958 Window B makes a request to the server and gets the status information
959 that should really go to Window A. For this reason, you may wish
960 to use the "query param" technique shown here in your applications.
963 =head1 EXPLORING THE POWER OF DBIC
965 In this section we will explore some additional capabilities offered
966 by DBIx::Class. Although these features have relatively little to do
967 with Catalyst per se, you will almost certainly want to take advantage
968 of them in your applications.
971 =head2 Add Datetime Columns to Our Existing Books Table
973 Let's add two columns to our existing C<books> table to track when
974 each book was added and when each book is updated:
977 sqlite> ALTER TABLE book ADD created INTEGER;
978 sqlite> ALTER TABLE book ADD updated INTEGER;
979 sqlite> UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
980 sqlite> SELECT * FROM book;
981 1|CCSP SNRS Exam Certification Guide|5|2009-03-08 16:26:35|2009-03-08 16:26:35
982 2|TCP/IP Illustrated, Volume 1|5|2009-03-08 16:26:35|2009-03-08 16:26:35
983 3|Internetworking with TCP/IP Vol.1|4|2009-03-08 16:26:35|2009-03-08 16:26:35
984 4|Perl Cookbook|5|2009-03-08 16:26:35|2009-03-08 16:26:35
985 5|Designing with Web Standards|5|2009-03-08 16:26:35|2009-03-08 16:26:35
986 9|TCP/IP Illustrated, Vol 3|5|2009-03-08 16:26:35|2009-03-08 16:26:35
990 This will modify the C<books> table to include the two new fields
991 and populate those fields with the current time.
994 =head2 Update DBIx::Class to Automatically Handle the Datetime Columns
996 Next, we should re-run the DBIC helper to update the Result Classes
999 $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
1000 create=static components=TimeStamp dbi:SQLite:myapp.db
1001 exists "/root/dev/MyApp/script/../lib/MyApp/Model"
1002 exists "/root/dev/MyApp/script/../t"
1003 Dumping manual schema for MyApp::Schema to directory /root/dev/MyApp/script/../lib ...
1004 Schema dump completed.
1005 exists "/root/dev/MyApp/script/../lib/MyApp/Model/DB.pm"
1007 Notice that we modified our use of the helper slightly: we told
1008 it to include the L<DBIx::Class::TimeStamp|DBIx::Class::TimeStamp>
1009 in the C<load_components> line of the Result Classes.
1011 If you open C<lib/MyApp/Schema/Result/Book.pm> in your editor you
1012 should see that the C<created> and C<updated> fields are now included
1013 in the call to C<add_columns()>, but our relationship information below
1014 the "C<# DO NOT MODIFY...>" line was automatically preserved.
1016 While we have this file open, let's update it with some additional
1017 information to have DBIC automatically handle the updating of these
1018 two fields for us. Insert the following code at the bottom of the
1019 file (it B<must> be B<below> the "C<# DO NOT MODIFY...>" line and
1020 B<above> the C<1;> on the last line):
1023 # Enable automatic date handling
1025 __PACKAGE__->add_columns(
1027 { data_type => 'datetime', set_on_create => 1 },
1029 { data_type => 'datetime', set_on_create => 1, set_on_update => 1 },
1032 This will override the definition for these fields that Schema::Loader
1033 placed at the top of the file. The C<set_on_create> and
1034 C<set_on_update> options will cause DBIx::Class to automatically
1035 update the timestamps in these columns whenever a row is created or
1038 To test this out, restart the development server using the
1039 C<DBIC_TRACE=1> option:
1041 DBIC_TRACE=1 script/myapp_server.pl
1043 Then enter the following URL into your web browser:
1045 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
1047 You should get the same "Book Created" screen we saw above. However,
1048 if you now use the sqlite3 command-line tool to dump the C<books> table,
1049 you will see that the new book we added has an appropriate date and
1050 time entered for it (see the last line in the listing below):
1052 $ sqlite3 myapp.db "select * from book"
1053 1|CCSP SNRS Exam Certification Guide|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1054 2|TCP/IP Illustrated, Volume 1|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1055 3|Internetworking with TCP/IP Vol.1|4|2009-03-08 16:26:35|2009-03-08 16:26:35
1056 4|Perl Cookbook|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1057 5|Designing with Web Standards|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1058 9|TCP/IP Illustrated, Vol 3|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1059 10|TCPIP_Illustrated_Vol-2|5|2009-03-08 16:29:08|2009-03-08 16:29:08
1061 Notice in the debug log that the SQL DBIC generated has changed to
1062 incorporate the datetime logic:
1064 INSERT INTO book ( created, rating, title, updated ) VALUES ( ?, ?, ?, ? ):
1065 '2009-05-25 20:39:41', '5', 'TCPIP_Illustrated_Vol-2', '2009-05-25 20:39:41'
1066 INSERT INTO book_author ( author_id, book_id ) VALUES ( ?, ? ): '4', '10'
1069 =head2 Create a ResultSet Class
1071 An often overlooked but extremely powerful features of DBIC is that it
1072 allows you to supply your own subclasses of C<DBIx::Class::ResultSet>.
1073 It allows you to pull complex and unsightly "query code" out of your
1074 controllers and encapsulate it in a method of your ResultSet Class.
1075 These "canned queries" in your ResultSet Class can then be invoked
1076 via a single call, resulting in much cleaner and easier to read
1079 To illustrate the concept with a fairly simple example, let's create a
1080 method that returns books added in the last 10 minutes. Start by
1081 making a directory where DBIx::Class will look for our ResultSet Class:
1083 $ mkdir lib/MyApp/Schema/ResultSet
1085 Then open C<lib/MyApp/Schema/ResultSet/Book.pm> and enter the following:
1087 package MyApp::Schema::ResultSet::Book;
1091 use base 'DBIx::Class::ResultSet';
1093 =head2 created_after
1095 A predefined search for recently added books
1100 my ($self, $datetime) = @_;
1102 my $date_str = $self->_source_handle->schema->storage
1103 ->datetime_parser->format_datetime($datetime);
1105 return $self->search({
1106 created => { '>' => $date_str }
1112 Then we need to tell the Result Class to to treat this as a ResultSet
1113 Class. Open C<lib/MyApp/Schema/Result/Book.pm> and add the following
1114 above the "C<1;>" at the bottom of the file:
1117 # Set ResultSet Class
1119 __PACKAGE__->resultset_class('MyApp::Schema::ResultSet::Book');
1121 Then add the following method to the C<lib/MyApp/Controller/Books.pm>:
1125 List recently created books
1129 sub list_recent :Chained('base') :PathPart('list_recent') :Args(1) {
1130 my ($self, $c, $mins) = @_;
1132 # Retrieve all of the book records as book model objects and store in the
1133 # stash where they can be accessed by the TT template, but only
1134 # retrieve books created within the last $min number of minutes
1135 $c->stash->{books} = [$c->model('DB::Book')
1136 ->created_after(DateTime->now->subtract(minutes => $mins))];
1138 # Set the TT template to use. You will almost always want to do this
1139 # in your action methods (action methods respond to user input in
1140 # your controllers).
1141 $c->stash->{template} = 'books/list.tt2';
1144 Now start the development server with C<DBIC_TRACE=1> and try
1145 different values for the minutes argument (the final number value) for
1146 the URL C<http://localhost:3000/books/list_recent/10>. For example,
1147 this would list all books added in the last fifteen minutes:
1149 http://localhost:3000/books/list_recent/15
1151 Depending on how recently you added books, you might want to
1152 try a higher or lower value.
1155 =head2 Chaining ResultSets
1157 One of the most helpful and powerful features in DBIx::Class is that
1158 it allows you to "chain together" a series of queries (note that this
1159 has nothing to do with the "Chained Dispatch" for Catalyst that we
1160 were discussing above). Because each ResultSet returns another
1161 ResultSet, you can take an initial query and immediately feed that
1162 into a second query (and so on for as many queries you need). Note
1163 that no matter how many ResultSets you chain together, the database
1164 itself will not be hit until you use a method that attempts to access
1165 the data. And, because this technique carries over to the ResultSet
1166 Class feature we implemented in the previous section for our "canned
1167 search", we can combine the two capabilities. For example, let's add
1168 an action to our C<Books> controller that lists books that are both
1169 recent I<and> have "TCP" in the title. Open up
1170 C<lib/MyApp/Controller/Books.pm> and add the following method:
1172 =head2 list_recent_tcp
1174 List recently created books
1178 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1179 my ($self, $c, $mins) = @_;
1181 # Retrieve all of the book records as book model objects and store in the
1182 # stash where they can be accessed by the TT template, but only
1183 # retrieve books created within the last $min number of minutes
1184 # AND that have 'TCP' in the title
1185 $c->stash->{books} = [$c->model('DB::Book')
1186 ->created_after(DateTime->now->subtract(minutes => $mins))
1187 ->search({title => {'like', '%TCP%'}})
1190 # Set the TT template to use. You will almost always want to do this
1191 # in your action methods (action methods respond to user input in
1192 # your controllers).
1193 $c->stash->{template} = 'books/list.tt2';
1196 To try this out, restart the development server with:
1198 DBIC_TRACE=1 script/myapp_server.pl
1200 And enter the following URL into your browser:
1202 http://localhost:3000/books/list_recent_tcp/100
1204 And you should get a list of books added in the last 100 minutes that
1205 contain the string "TCP" in the title. However, if you look at all
1206 books within the last 100 minutes, you should get a longer list
1207 (again, you might have to adjust the number of minutes depending on
1208 how recently you added books to your database):
1210 http://localhost:3000/books/list_recent/100
1212 Take a look at the DBIC_TRACE output in the development server log for
1213 the first URL and you should see something similar to the following:
1215 SELECT me.id, me.title, me.rating, me.created, me.updated FROM book me
1216 WHERE ( ( title LIKE ? AND created > ? ) ): '%TCP%', '2009-05-25 19:09:13'
1218 However, let's not pollute our controller code with this raw "TCP"
1219 query -- it would be cleaner to encapsulate that code in a method on
1220 our ResultSet Class. To do this, open
1221 C<lib/MyApp/Schema/ResultSet/Book.pm> and add the following method:
1225 A predefined search for books with a 'LIKE' search in the string
1230 my ($self, $title_str) = @_;
1232 return $self->search({
1233 title => { 'like' => "%$title_str%" }
1237 We defined the search string as C<$title_str> to make the method more
1238 flexible. Now update the C<list_recent_tcp> method in
1239 C<lib/MyApp/Controller/Books.pm> to match the following (we have
1240 replaced the C<-E<gt>search> line with the C<-E<gt>title_like> line
1241 shown here -- the rest of the method should be the same):
1243 =head2 list_recent_tcp
1245 List recently created books
1249 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1250 my ($self, $c, $mins) = @_;
1252 # Retrieve all of the book records as book model objects and store in the
1253 # stash where they can be accessed by the TT template, but only
1254 # retrieve books created within the last $min number of minutes
1255 # AND that have 'TCP' in the title
1256 $c->stash->{books} = [$c->model('DB::Book')
1257 ->created_after(DateTime->now->subtract(minutes => $mins))
1261 # Set the TT template to use. You will almost always want to do this
1262 # in your action methods (action methods respond to user input in
1263 # your controllers).
1264 $c->stash->{template} = 'books/list.tt2';
1267 Then restart the development server and try out the C<list_recent_tcp>
1268 and C<list_recent> URL as we did above. It should work just the same,
1269 but our code is obviously cleaner and more modular, while also being
1270 more flexible at the same time.
1273 =head2 Adding Methods to Result Classes
1275 In the previous two sections we saw a good example of how we could use
1276 DBIx::Class ResultSet Classes to clean up our code for an entire query
1277 (for example, our "canned searches" that filtered the entire query).
1278 We can do a similar improvement when working with individual rows as
1279 well. Whereas the ResultSet construct is used in DBIC to correspond
1280 to an entire query, the Result Class construct is used to represent a
1281 row. Therefore, we can add row-specific "helper methods" to our Result
1282 Classes stored in C<lib/MyApp/Schema/Result/>. For example, open
1283 C<lib/MyApp/Schema/Result/Author.pm> and add the following method (as
1284 always, it must be above the closing "C<1;>"):
1292 return $self->first_name . ' ' . $self->last_name;
1295 This will allow us to conveniently retrieve both the first and last
1296 name for an author in one shot. Now open C<root/src/books/list.tt2>
1297 and change the definition of C<tt_authors> from this:
1300 [% tt_authors = [ ];
1301 tt_authors.push(author.last_name) FOREACH author = book.authors %]
1307 [% tt_authors = [ ];
1308 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1311 (Only C<author.last_name> was changed to C<author.full_name> -- the
1312 rest of the file should remain the same.)
1314 Now restart the development server and go to the standard book list
1317 http://localhost:3000/books/list
1319 The "Author(s)" column will now contain both the first and last name.
1320 And, because the concatenation logic was encapsulated inside our
1321 Result Class, it keeps the code inside our TT template nice and clean
1322 (remember, we want the templates to be as close to pure HTML markup as
1323 possible). Obviously, this capability becomes even more useful as you
1324 use to to remove even more complicated row-specific logic from your
1328 =head2 Moving Complicated View Code to the Model
1330 The previous section illustrated how we could use a Result Class
1331 method to print the full names of the authors without adding any extra
1332 code to our view, but it still left us with a fairly ugly mess (see
1333 C<root/src/books/list.tt2>):
1337 [% # NOTE: See Chapter 4 for a better way to do this! -%]
1338 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
1339 [% # loop in 'side effect notation' to load just the last names of the -%]
1340 [% # authors into the list. Note that the 'push' TT vmethod does not print -%]
1341 [% # a value, so nothing will be printed here. But, if you have something -%]
1342 [% # in TT that does return a method and you don't want it printed, you -%]
1343 [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to -%]
1344 [% # call it and discard the return value. -%]
1345 [% tt_authors = [ ];
1346 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1347 [% # Now use a TT 'virtual method' to display the author count in parens -%]
1348 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
1349 ([% tt_authors.size | html %])
1350 [% # Use another TT vmethod to join & print the names & comma separators -%]
1351 [% tt_authors.join(', ') | html %]
1355 Let's combine some of the techniques used earlier in this section to
1356 clean this up. First, let's add a method to our Book Result Class to
1357 return the number of authors for a book. Open
1358 C<lib/MyApp/Schema/Result/Book.pm> and add the following method:
1362 Return the number of authors for the current book
1369 # Use the 'many_to_many' relationship to fetch all of the authors for the current
1370 # and the 'count' method in DBIx::Class::ResultSet to get a SQL COUNT
1371 return $self->authors->count;
1374 Next, let's add a method to return a list of authors for a book to the
1375 same C<lib/MyApp/Schema/Result/Book.pm> file:
1379 Return a comma-separated list of authors for the current book
1386 # Loop through all authors for the current book, calling all the 'full_name'
1387 # Result Class method for each
1389 foreach my $author ($self->authors) {
1390 push(@names, $author->full_name);
1393 return join(', ', @names);
1396 This method loops through each author, using the C<full_name> Result
1397 Class method we added to C<lib/MyApp/Schema/Result/Author.pm> in the
1400 Using these two methods, we can simplify our TT code. Open
1401 C<root/src/books/list.tt2> and update the "Author(s)" table cell to
1402 match the following:
1406 [% # Print count and author list using Result Class methods -%]
1407 ([% book.author_count | html %]) [% book.author_list | html %]
1411 Although most of the code we removed comprised comments, the overall
1412 effect is dramatic... because our view code is so simple, we don't
1413 huge comments to clue people in to the gist of our code. The view
1414 code is now self-documenting and readable enough that you could
1415 probably get by with no comments at all. All of the "complex" work is
1416 being done in our Result Class methods (and, because we have broken
1417 the code into nice, modular chucks, the Result Class code is hardly
1418 something you would call complex).
1420 As we saw in this section, always strive to keep your view AND
1421 controller code as simple as possible by pulling code out into your
1422 model objects. Because DBIx::Class can be easily extended in so many
1423 ways, it's an excellent to way accomplish this objective. It will
1424 make your code cleaner, easier to write, less error-prone, and easier
1425 to debug and maintain.
1427 Before you conclude this section, fire up the development server and
1428 hit Refresh in your browser... the output should be the same even
1429 though the backend code has been trimmed down.
1434 Kennedy Clark, C<hkclark@gmail.com>
1436 Please report any errors, issues or suggestions to the author. The
1437 most recent version of the Catalyst Tutorial can be found at
1438 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.
1440 Copyright 2006-2008, Kennedy Clark, under Creative Commons License
1441 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).