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'
237 (The '\' characters won't actually appear in the output -- we are
238 using them as "line continuation markers" here.)
241 =head1 CONVERT TO A CHAINED ACTION
243 Although the example above uses the same C<Local> action type for the
244 method that we saw in the previous chapter of the tutorial, there is an
245 alternate approach that allows us to be more specific while also
246 paving the way for more advanced capabilities. Change the method
247 declaration for C<url_create> in C<lib/MyApp/Controller/Books.pm> you
248 entered above to match the following:
250 sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
251 # In addition to self & context, get the title, rating, &
252 # author_id args from the URL. Note that Catalyst automatically
253 # puts the first 3 arguments worth of extra information after the
254 # "/<controller_name>/<action_name/" into @_ because we specified
255 # "Args(3)". The args are separated by the '/' char on the URL.
256 my ($self, $c, $title, $rating, $author_id) = @_;
260 This converts the method to take advantage of the Chained
261 action/dispatch type. Chaining lets you have a single URL
262 automatically dispatch to several controller methods, each of which
263 can have precise control over the number of arguments that it will
264 receive. A chain can essentially be thought of having three parts --
265 a beginning, a middle, and an end. The bullets below summarize the key
266 points behind each of these parts of a chain:
280 B<Use "C<:Chained('/')>" to start a chain>
284 Get arguments through C<CaptureArgs()>
288 Specify the path to match with C<PathPart()>
301 Link to previous part of the chain with C<:Chained('_name_')>
305 Get arguments through C<CaptureArgs()>
309 Specify the path to match with C<PathPart()>
322 Link to previous part of the chain with C<:Chained('_name_')>
326 B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
330 Specify the path to match with C<PathPart()>
337 In our C<url_create> method above, we have combined all three parts into
338 a single method: C<:Chained('/')> to start the chain,
339 C<:PathPart('books/url_create')> to specify the base URL to match, and
340 C<:Args(3)> to capture exactly three arguments and to end the chain.
342 As we will see shortly, a chain can consist of as many "links" as you
343 wish, with each part capturing some arguments and doing some work
344 along the way. We will continue to use the Chained action type in this
345 chapter of the tutorial and explore slightly more advanced capabilities
346 with the base method and delete feature below. But Chained dispatch
347 is capable of far more. For additional information, see
348 L<Catalyst::Manual::Intro/Action types>,
349 L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained>,
350 and the 2006 Advent calendar entry on the subject:
351 L<http://www.catalystframework.org/calendar/2006/10>.
354 =head2 Try the Chained Action
356 If you look back at the development server startup logs from your
357 initial version of the C<url_create> method (the one using the
358 C<:Local> attribute), you will notice that it produced output similar
361 [debug] Loaded Path actions:
362 .-------------------------------------+--------------------------------------.
364 +-------------------------------------+--------------------------------------+
367 | /books | /books/index |
368 | /books/list | /books/list |
369 | /books/url_create | /books/url_create |
370 '-------------------------------------+--------------------------------------'
372 Now start the development server with our basic chained method in
373 place and the startup debug output should change to something along
374 the lines of the following:
376 [debug] Loaded Path actions:
377 .-------------------------------------+--------------------------------------.
379 +-------------------------------------+--------------------------------------+
382 | /books | /books/index |
383 | /books/list | /books/list |
384 '-------------------------------------+--------------------------------------'
386 [debug] Loaded Chained actions:
387 .-------------------------------------+--------------------------------------.
388 | Path Spec | Private |
389 +-------------------------------------+--------------------------------------+
390 | /books/url_create/*/*/* | /books/url_create |
391 '-------------------------------------+--------------------------------------'
393 C<url_create> has disappeared form the "Loaded Path actions" section
394 but it now shows up under the newly created "Loaded Chained actions"
395 section. And the "/*/*/*" portion clearly shows our requirement for
398 As with our non-chained version of C<url_create>, use your browser to
399 enter the following URL:
401 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
403 You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
404 'Stevens' with a rating of 5." along with a dump of the new book model
405 object. Click the "Return to list" link, and you should find that there
406 are now seven books shown (two copies of I<TCPIP_Illustrated_Vol-2>).
409 =head2 Refactor to Use a 'base' Method to Start the Chains
411 Let's make a quick update to our initial Chained action to show a
412 little more of the power of chaining. First, open
413 C<lib/MyApp/Controller/Books.pm> in your editor and add the following
418 Can place common logic to start chained dispatch here
422 sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
425 # Store the ResultSet in stash so it's available for other methods
426 $c->stash->{resultset} = $c->model('DB::Book');
428 # Print a message to the debug log
429 $c->log->debug('*** INSIDE BASE METHOD ***');
432 Here we print a log message and store the DBIC ResultSet in
433 C<$c-E<gt>stash-E<gt>{resultset}> so that it's automatically available
434 for other actions that chain off C<base>. If your controller always
435 needs a book ID as its first argument, you could have the base method
436 capture that argument (with C<:CaptureArgs(1)>) and use it to pull the
437 book object with C<-E<gt>find($id)> and leave it in the stash for
438 later parts of your chains to then act upon. Because we have several
439 actions that don't need to retrieve a book (such as the C<url_create>
440 we are working with now), we will instead add that functionality
441 to a common C<object> action shortly.
443 As for C<url_create>, let's modify it to first dispatch to C<base>.
444 Open up C<lib/MyApp/Controller/Books.pm> and edit the declaration for
445 C<url_create> to match the following:
447 sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
449 Next, try out the refactored chain by restarting the development
450 server. Notice that our "Loaded Chained actions" section has changed
453 [debug] Loaded Chained actions:
454 .-------------------------------------+--------------------------------------.
455 | Path Spec | Private |
456 +-------------------------------------+--------------------------------------+
457 | /books/url_create/*/*/* | /books/base (0) |
458 | | => /books/url_create |
459 '-------------------------------------+--------------------------------------'
461 The "Path Spec" is the same, but now it maps to two Private actions as
462 we would expect. The C<base> method is being triggered by the
463 C</books> part of the URL. However, the processing then continues to
464 the C<url_create> method because this method "chained" off C<base> and
465 specified C<:PathPart('url_create')> (note that we could have omitted
466 the "PathPart" here because it matches the name of the method, but we
467 will include it to make the logic as explicit as possible).
469 Once again, enter the following URL into your browser:
471 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
473 The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
474 rating of 5." message and a dump of the new book object should appear.
475 Also notice the extra "INSIDE BASE METHOD" debug message in the
476 development server output from the C<base> method. Click the "Return
477 to list" link, and you should find that there are now eight books
478 shown. (You may have a larger number of books if you repeated any of
479 the "create" actions more than once. Don't worry about it as long as
480 the number of books is appropriate for the number of times you added
481 new books... there should be the original five books added via
482 C<myapp01.sql> plus one additional book for each time you ran one
483 of the url_create variations above.)
486 =head1 MANUALLY BUILDING A CREATE FORM
488 Although the C<url_create> action in the previous step does begin to
489 reveal the power and flexibility of both Catalyst and DBIC, it's
490 obviously not a very realistic example of how users should be expected
491 to enter data. This section begins to address that concern.
494 =head2 Add Method to Display The Form
496 Edit C<lib/MyApp/Controller/Books.pm> and add the following method:
500 Display form to collect information for book to create
504 sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
507 # Set the TT template to use
508 $c->stash->{template} = 'books/form_create.tt2';
511 This action simply invokes a view containing a form to create a book.
514 =head2 Add a Template for the Form
516 Open C<root/src/books/form_create.tt2> in your editor and enter:
518 [% META title = 'Manual Form Book Create' -%]
520 <form method="post" action="[% c.uri_for('form_create_do') %]">
522 <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
523 <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
524 <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
526 <input type="submit" name="Submit" value="Submit">
529 Note that we have specified the target of the form data as
530 C<form_create_do>, the method created in the section that follows.
533 =head2 Add a Method to Process Form Values and Update Database
535 Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
536 save the form information to the database:
538 =head2 form_create_do
540 Take information from form and add to database
544 sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
547 # Retrieve the values from the form
548 my $title = $c->request->params->{title} || 'N/A';
549 my $rating = $c->request->params->{rating} || 'N/A';
550 my $author_id = $c->request->params->{author_id} || '1';
553 my $book = $c->model('DB::Book')->create({
557 # Handle relationship with author
558 $book->add_to_book_authors({author_id => $author_id});
559 # Note: Above is a shortcut for this:
560 # $book->create_related('book_authors', {author_id => $author_id});
562 # Store new model object in stash
563 $c->stash->{book} = $book;
565 # Avoid Data::Dumper issue mentioned earlier
566 # You can probably omit this
567 $Data::Dumper::Useperl = 1;
569 # Set the TT template to use
570 $c->stash->{template} = 'books/create_done.tt2';
574 =head2 Test Out The Form
576 If the application is still running from before, use C<Ctrl-C> to kill
577 it. Then restart the server:
579 $ script/myapp_server.pl
581 Notice that the server startup log reflects the two new chained
582 methods that we added:
584 [debug] Loaded Chained actions:
585 .-------------------------------------+--------------------------------------.
586 | Path Spec | Private |
587 +-------------------------------------+--------------------------------------+
588 | /books/form_create | /books/base (0) |
589 | | => /books/form_create |
590 | /books/form_create_do | /books/base (0) |
591 | | => /books/form_create_do |
592 | /books/url_create/*/*/* | /books/base (0) |
593 | | => /books/url_create |
594 '-------------------------------------+--------------------------------------'
596 Point your browser to L<http://localhost:3000/books/form_create> and
597 enter "TCP/IP Illustrated, Vol 3" for the title, a rating of 5, and an
598 author ID of 4. You should then see the output of the same
599 C<create_done.tt2> template seen in earlier examples. Finally, click
600 "Return to list" to view the full list of books.
602 B<Note:> Having the user enter the primary key ID for the author is
603 obviously crude; we will address this concern with a drop-down list and
604 add validation to our forms in Chapter 9.
607 =head1 A SIMPLE DELETE FEATURE
609 Turning our attention to the Delete portion of CRUD, this section
610 illustrates some basic techniques that can be used to remove information
614 =head2 Include a Delete Link in the List
616 Edit C<root/src/books/list.tt2> and update it to match the following (two
617 sections have changed: 1) the additional '<th>Links</th>' table header,
618 and 2) the four lines for the Delete link near the bottom):
620 [% # This is a TT comment. The '-' at the end "chomps" the newline. You won't -%]
621 [% # see this "chomping" in your browser because HTML ignores blank lines, but -%]
622 [% # it WILL eliminate a blank line if you view the HTML source. It's purely -%]
623 [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
625 [% # Provide a title -%]
626 [% META title = 'Book List' -%]
629 <tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
630 [% # Display each book in a table row %]
631 [% FOREACH book IN books -%]
633 <td>[% book.title %]</td>
634 <td>[% book.rating %]</td>
636 [% # NOTE: See "Exploring The Power of DBIC" for a better way to do this! -%]
637 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
638 [% # loop in 'side effect notation' to load just the last names of the -%]
639 [% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
640 [% # a value, so nothing will be printed here. But, if you have something -%]
641 [% # in TT that does return a value and you don't want it printed, you can -%]
642 [% # 1) assign it to a bogus value, or -%]
643 [% # 2) use the CALL keyword to call it and discard the return value. -%]
645 tt_authors.push(author.last_name) FOREACH author = book.authors %]
646 [% # Now use a TT 'virtual method' to display the author count in parens -%]
647 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
648 ([% tt_authors.size | html %])
649 [% # Use another TT vmethod to join & print the names & comma separators -%]
650 [% tt_authors.join(', ') | html %]
653 [% # Add a link to delete a book %]
654 <a href="[% c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
660 The additional code is obviously designed to add a new column to the
661 right side of the table with a C<Delete> "button" (for simplicity, links
662 will be used instead of full HTML buttons; in practice, anything that
663 modifies data should be handled with a form sending a POST request).
665 Also notice that we are using a more advanced form of C<uri_for> than
666 we have seen before. Here we use
667 C<$c-E<gt>controller-E<gt>action_for> to automatically generate a URI
668 appropriate for that action based on the method we want to link to
669 while inserting the C<book.id> value into the appropriate place. Now,
670 if you ever change C<:PathPart('delete')> in your controller method to
671 C<:PathPart('kill')>, then your links will automatically update
672 without any changes to your .tt2 template file. As long as the name
673 of your method does not change (here, "delete"), then your links will
674 still be correct. There are a few shortcuts and options when using
681 If you are referring to a method in the current controller, you can
682 use C<$self-E<gt>action_for('_method_name_')>.
686 If you are referring to a method in a different controller, you need
687 to include that controller's name as an argument to C<controller()>, as in
688 C<$c-E<gt>controller('_controller_name_')-E<gt>action_for('_method_name_')>.
692 B<Note:> In practice you should B<never> use a GET request to delete a
693 record -- always use POST for actions that will modify data. We are
694 doing it here for illustrative and simplicity purposes only.
697 =head2 Add a Common Method to Retrieve a Book for the Chain
699 As mentioned earlier, since we have a mixture of actions that operate
700 on a single book ID and others that do not, we should not have C<base>
701 capture the book ID, find the corresponding book in the database and
702 save it in the stash for later links in the chain. However, just
703 because that logic does not belong in C<base> doesn't mean that we
704 can't create another location to centralize the book lookup code. In
705 our case, we will create a method called C<object> that will store the
706 specific book in the stash. Chains that always operate on a single
707 existing book can chain off this method, but methods such as
708 C<url_create> that don't operate on an existing book can chain
711 To add the C<object> method, edit C<lib/MyApp/Controller/Books.pm>
712 and add the following code:
716 Fetch the specified book object based on the book ID and store
721 sub object :Chained('base') :PathPart('id') :CaptureArgs(1) {
722 # $id = primary key of book to delete
723 my ($self, $c, $id) = @_;
725 # Find the book object and store it in the stash
726 $c->stash(object => $c->stash->{resultset}->find($id));
728 # Make sure the lookup was successful. You would probably
729 # want to do something like this in a real app:
730 # $c->detach('/error_404') if !$c->stash->{object};
731 die "Book $id not found!" if !$c->stash->{object};
733 # Print a message to the debug log
734 $c->log->debug("*** INSIDE OBJECT METHOD for obj id=$id ***");
737 Now, any other method that chains off C<object> will automatically
738 have the appropriate book waiting for it in
739 C<$c-E<gt>stash-E<gt>{object}>.
741 Also note that we are using a different technique for setting
742 C<$c-E<gt>stash>. The advantage of this style is that it lets you set
743 multiple stash variables at a time. For example:
745 $c->stash(object => $c->stash->{resultset}->find($id),
750 $c->stash({object => $c->stash->{resultset}->find($id),
751 another_thing => 1});
753 Either format works, but the C<$c-E<gt>stash(name =E<gt> value);>
754 style is growing in popularity -- you may wish to use it all
755 the time (even when you are only setting a single value).
758 =head2 Add a Delete Action to the Controller
760 Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
769 sub delete :Chained('object') :PathPart('delete') :Args(0) {
772 # Use the book object saved by 'object' and delete it along
773 # with related 'book_author' entries
774 $c->stash->{object}->delete;
776 # Set a status message to be displayed at the top of the view
777 $c->stash->{status_msg} = "Book deleted.";
779 # Forward to the list action/method in this controller
783 This method first deletes the book object saved by the C<object> method.
784 However, it also removes the corresponding entry from the
785 C<book_author> table with a cascading delete.
787 Then, rather than forwarding to a "delete done" page as we did with the
788 earlier create example, it simply sets the C<status_msg> to display a
789 notification to the user as the normal list view is rendered.
791 The C<delete> action uses the context C<forward> method to return the
792 user to the book list. The C<detach> method could have also been used.
793 Whereas C<forward> I<returns> to the original action once it is
794 completed, C<detach> does I<not> return. Other than that, the two are
798 =head2 Try the Delete Feature
800 If the application is still running from before, use C<Ctrl-C> to kill
801 it. Then restart the server:
803 $ DBIC_TRACE=1 script/myapp_server.pl
805 The C<delete> method now appears in the "Loaded Chained actions" section
806 of the startup debug output:
808 [debug] Loaded Chained actions:
809 .-------------------------------------+--------------------------------------.
810 | Path Spec | Private |
811 +-------------------------------------+--------------------------------------+
812 | /books/id/*/delete | /books/base (0) |
813 | | -> /books/object (1) |
814 | | => /books/delete |
815 | /books/form_create | /books/base (0) |
816 | | => /books/form_create |
817 | /books/form_create_do | /books/base (0) |
818 | | => /books/form_create_do |
819 | /books/url_create/*/*/* | /books/base (0) |
820 | | => /books/url_create |
821 '-------------------------------------+--------------------------------------'
823 Then point your browser to L<http://localhost:3000/books/list> and click
824 the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
825 "Book deleted" status message should display at the top of the page,
826 along with a list of the eight remaining books. You will also see the
827 cascading delete operation via the DBIC_TRACE output:
829 SELECT me.id, me.title, me.rating FROM book me WHERE ( ( me.id = ? ) ): '6'
830 DELETE FROM book WHERE ( id = ? ): '6'
831 SELECT me.book_id, me.author_id FROM book_author me WHERE ( me.book_id = ? ): '6'
832 DELETE FROM book_author WHERE ( author_id = ? AND book_id = ? ): '4', '6'
835 =head2 Fixing a Dangerous URL
837 Note the URL in your browser once you have performed the deletion in the
838 prior step -- it is still referencing the delete action:
840 http://localhost:3000/books/id/6/delete
842 What if the user were to press reload with this URL still active? In
843 this case the redundant delete is harmless (although it does generate
844 an exception screen, it doesn't perform any undesirable actions on the
845 application or database), but in other cases this could clearly be
848 We can improve the logic by converting to a redirect. Unlike
849 C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform
850 a server-side alteration in the flow of processing, a redirect is a
851 client-side mechanism that causes the browser to issue an entirely
852 new request. As a result, the URL in the browser is updated to match
853 the destination of the redirection URL.
855 To convert the forward used in the previous section to a redirect,
856 open C<lib/MyApp/Controller/Books.pm> and edit the existing
857 C<sub delete> method to match:
865 sub delete :Chained('object') :PathPart('delete') :Args(0) {
868 # Use the book object saved by 'object' and delete it along
869 # with related 'book_author' entries
870 $c->stash->{object}->delete;
872 # Set a status message to be displayed at the top of the view
873 $c->stash->{status_msg} = "Book deleted.";
875 # Redirect the user back to the list page. Note the use
876 # of $self->action_for as earlier in this section (BasicCRUD)
877 $c->response->redirect($c->uri_for($self->action_for('list')));
881 =head2 Try the Delete and Redirect Logic
883 Restart the development server and point your browser to
884 L<http://localhost:3000/books/list> (don't just hit "Refresh" in your
885 browser since we left the URL in an invalid state in the previous
886 section!) and delete the first copy of the remaining two
887 "TCPIP_Illustrated_Vol-2" books. The URL in your browser should return
888 to the L<http://localhost:3000/books/list> URL, so that is an
889 improvement, but notice that I<no green "Book deleted" status message is
890 displayed>. Because the stash is reset on every request (and a redirect
891 involves a second request), the C<status_msg> is cleared before it can
895 =head2 Using 'uri_for' to Pass Query Parameters
897 There are several ways to pass information across a redirect. One
898 option is to use the C<flash> technique that we will see in Chapter 5
899 of this tutorial; however, here we will pass the information via query
900 parameters on the redirect itself. Open
901 C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
902 method to match the following:
910 sub delete :Chained('object') :PathPart('delete') :Args(0) {
913 # Use the book object saved by 'object' and delete it along
914 # with related 'book_author' entries
915 $c->stash->{object}->delete;
917 # Redirect the user back to the list page with status msg as an arg
918 $c->response->redirect($c->uri_for($self->action_for('list'),
919 {status_msg => "Book deleted."}));
922 This modification simply leverages the ability of C<uri_for> to include
923 an arbitrary number of name/value pairs in a hash reference. Next, we
924 need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
929 [%# Status and error messages %]
930 <span class="message">[% status_msg || c.request.params.status_msg %]</span>
931 <span class="error">[% error_msg %]</span>
932 [%# This is where TT will stick all of your template's contents. -%]
934 </div><!-- end content -->
937 Although the sample above only shows the C<content> div, leave the
938 rest of the file intact -- the only change we made to the C<wrapper.tt2>
939 was to add "C<|| c.request.params.status_msg>" to the
940 C<E<lt>span class="message"E<gt>> line.
943 =head2 Try the Delete and Redirect With Query Param Logic
945 Restart the development server and point your browser to
946 L<http://localhost:3000/books/list> (you should now be able to safely
947 hit "refresh" in your browser). Then delete the remaining copy of
948 "TCPIP_Illustrated_Vol-2". The green "Book deleted" status message
951 B<NOTE:> Another popular method for maintaining server-side
952 information across a redirect is to use the C<flash> technique we
953 discuss in the next chapter of the tutorial,
954 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>. While
955 C<flash> is a "slicker" mechanism in that it's all handled by the
956 server and doesn't "pollute" your URLs, B<it is important to note that
957 C<flash> can lead to situations where the wrong information shows up
958 in the wrong browser window if the user has multiple windows or
959 browser tabs open>. For example, Window A causes something to be
960 placed in the stash, but before that window performs a redirect,
961 Window B makes a request to the server and gets the status information
962 that should really go to Window A. For this reason, you may wish
963 to use the "query param" technique shown here in your applications.
966 =head1 EXPLORING THE POWER OF DBIC
968 In this section we will explore some additional capabilities offered
969 by DBIx::Class. Although these features have relatively little to do
970 with Catalyst per se, you will almost certainly want to take advantage
971 of them in your applications.
974 =head2 Add Datetime Columns to Our Existing Books Table
976 Let's add two columns to our existing C<books> table to track when
977 each book was added and when each book is updated:
980 sqlite> ALTER TABLE book ADD created INTEGER;
981 sqlite> ALTER TABLE book ADD updated INTEGER;
982 sqlite> UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
983 sqlite> SELECT * FROM book;
984 1|CCSP SNRS Exam Certification Guide|5|2009-03-08 16:26:35|2009-03-08 16:26:35
985 2|TCP/IP Illustrated, Volume 1|5|2009-03-08 16:26:35|2009-03-08 16:26:35
986 3|Internetworking with TCP/IP Vol.1|4|2009-03-08 16:26:35|2009-03-08 16:26:35
987 4|Perl Cookbook|5|2009-03-08 16:26:35|2009-03-08 16:26:35
988 5|Designing with Web Standards|5|2009-03-08 16:26:35|2009-03-08 16:26:35
989 9|TCP/IP Illustrated, Vol 3|5|2009-03-08 16:26:35|2009-03-08 16:26:35
993 This will modify the C<books> table to include the two new fields
994 and populate those fields with the current time.
997 =head2 Update DBIx::Class to Automatically Handle the Datetime Columns
999 Next, we should re-run the DBIC helper to update the Result Classes
1000 with the new fields:
1002 $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
1003 create=static components=TimeStamp dbi:SQLite:myapp.db
1004 exists "/root/dev/MyApp/script/../lib/MyApp/Model"
1005 exists "/root/dev/MyApp/script/../t"
1006 Dumping manual schema for MyApp::Schema to directory /root/dev/MyApp/script/../lib ...
1007 Schema dump completed.
1008 exists "/root/dev/MyApp/script/../lib/MyApp/Model/DB.pm"
1010 Notice that we modified our use of the helper slightly: we told
1011 it to include the L<DBIx::Class::TimeStamp|DBIx::Class::TimeStamp>
1012 in the C<load_components> line of the Result Classes.
1014 If you open C<lib/MyApp/Schema/Result/Book.pm> in your editor you
1015 should see that the C<created> and C<updated> fields are now included
1016 in the call to C<add_columns()>, but our relationship information below
1017 the "C<# DO NOT MODIFY...>" line was automatically preserved.
1019 While we have this file open, let's update it with some additional
1020 information to have DBIC automatically handle the updating of these
1021 two fields for us. Insert the following code at the bottom of the
1022 file (it B<must> be B<below> the "C<# DO NOT MODIFY...>" line and
1023 B<above> the C<1;> on the last line):
1026 # Enable automatic date handling
1028 __PACKAGE__->add_columns(
1030 { data_type => 'datetime', set_on_create => 1 },
1032 { data_type => 'datetime', set_on_create => 1, set_on_update => 1 },
1035 This will override the definition for these fields that Schema::Loader
1036 placed at the top of the file. The C<set_on_create> and
1037 C<set_on_update> options will cause DBIx::Class to automatically
1038 update the timestamps in these columns whenever a row is created or
1041 To test this out, restart the development server using the
1042 C<DBIC_TRACE=1> option:
1044 DBIC_TRACE=1 script/myapp_server.pl
1046 Then enter the following URL into your web browser:
1048 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
1050 You should get the same "Book Created" screen we saw above. However,
1051 if you now use the sqlite3 command-line tool to dump the C<books> table,
1052 you will see that the new book we added has an appropriate date and
1053 time entered for it (see the last line in the listing below):
1055 $ sqlite3 myapp.db "select * from book"
1056 1|CCSP SNRS Exam Certification Guide|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1057 2|TCP/IP Illustrated, Volume 1|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1058 3|Internetworking with TCP/IP Vol.1|4|2009-03-08 16:26:35|2009-03-08 16:26:35
1059 4|Perl Cookbook|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1060 5|Designing with Web Standards|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1061 9|TCP/IP Illustrated, Vol 3|5|2009-03-08 16:26:35|2009-03-08 16:26:35
1062 10|TCPIP_Illustrated_Vol-2|5|2009-03-08 16:29:08|2009-03-08 16:29:08
1064 Notice in the debug log that the SQL DBIC generated has changed to
1065 incorporate the datetime logic:
1067 INSERT INTO book ( created, rating, title, updated ) VALUES ( ?, ?, ?, ? ):
1068 '2009-05-25 20:39:41', '5', 'TCPIP_Illustrated_Vol-2', '2009-05-25 20:39:41'
1069 INSERT INTO book_author ( author_id, book_id ) VALUES ( ?, ? ): '4', '10'
1072 =head2 Create a ResultSet Class
1074 An often overlooked but extremely powerful features of DBIC is that it
1075 allows you to supply your own subclasses of C<DBIx::Class::ResultSet>.
1076 It allows you to pull complex and unsightly "query code" out of your
1077 controllers and encapsulate it in a method of your ResultSet Class.
1078 These "canned queries" in your ResultSet Class can then be invoked
1079 via a single call, resulting in much cleaner and easier to read
1082 To illustrate the concept with a fairly simple example, let's create a
1083 method that returns books added in the last 10 minutes. Start by
1084 making a directory where DBIx::Class will look for our ResultSet Class:
1086 $ mkdir lib/MyApp/Schema/ResultSet
1088 Then open C<lib/MyApp/Schema/ResultSet/Book.pm> and enter the following:
1090 package MyApp::Schema::ResultSet::Book;
1094 use base 'DBIx::Class::ResultSet';
1096 =head2 created_after
1098 A predefined search for recently added books
1103 my ($self, $datetime) = @_;
1105 my $date_str = $self->_source_handle->schema->storage
1106 ->datetime_parser->format_datetime($datetime);
1108 return $self->search({
1109 created => { '>' => $date_str }
1115 Then we need to tell the Result Class to to treat this as a ResultSet
1116 Class. Open C<lib/MyApp/Schema/Result/Book.pm> and add the following
1117 above the "C<1;>" at the bottom of the file:
1120 # Set ResultSet Class
1122 __PACKAGE__->resultset_class('MyApp::Schema::ResultSet::Book');
1124 Then add the following method to the C<lib/MyApp/Controller/Books.pm>:
1128 List recently created books
1132 sub list_recent :Chained('base') :PathPart('list_recent') :Args(1) {
1133 my ($self, $c, $mins) = @_;
1135 # Retrieve all of the book records as book model objects and store in the
1136 # stash where they can be accessed by the TT template, but only
1137 # retrieve books created within the last $min number of minutes
1138 $c->stash->{books} = [$c->model('DB::Book')
1139 ->created_after(DateTime->now->subtract(minutes => $mins))];
1141 # Set the TT template to use. You will almost always want to do this
1142 # in your action methods (action methods respond to user input in
1143 # your controllers).
1144 $c->stash->{template} = 'books/list.tt2';
1147 Now start the development server with C<DBIC_TRACE=1> and try
1148 different values for the minutes argument (the final number value) for
1149 the URL C<http://localhost:3000/books/list_recent/10>. For example,
1150 this would list all books added in the last fifteen minutes:
1152 http://localhost:3000/books/list_recent/15
1154 Depending on how recently you added books, you might want to
1155 try a higher or lower value.
1158 =head2 Chaining ResultSets
1160 One of the most helpful and powerful features in DBIx::Class is that
1161 it allows you to "chain together" a series of queries (note that this
1162 has nothing to do with the "Chained Dispatch" for Catalyst that we
1163 were discussing above). Because each ResultSet returns another
1164 ResultSet, you can take an initial query and immediately feed that
1165 into a second query (and so on for as many queries you need). Note
1166 that no matter how many ResultSets you chain together, the database
1167 itself will not be hit until you use a method that attempts to access
1168 the data. And, because this technique carries over to the ResultSet
1169 Class feature we implemented in the previous section for our "canned
1170 search", we can combine the two capabilities. For example, let's add
1171 an action to our C<Books> controller that lists books that are both
1172 recent I<and> have "TCP" in the title. Open up
1173 C<lib/MyApp/Controller/Books.pm> and add the following method:
1175 =head2 list_recent_tcp
1177 List recently created books
1181 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1182 my ($self, $c, $mins) = @_;
1184 # Retrieve all of the book records as book model objects and store in the
1185 # stash where they can be accessed by the TT template, but only
1186 # retrieve books created within the last $min number of minutes
1187 # AND that have 'TCP' in the title
1188 $c->stash->{books} = [$c->model('DB::Book')
1189 ->created_after(DateTime->now->subtract(minutes => $mins))
1190 ->search({title => {'like', '%TCP%'}})
1193 # Set the TT template to use. You will almost always want to do this
1194 # in your action methods (action methods respond to user input in
1195 # your controllers).
1196 $c->stash->{template} = 'books/list.tt2';
1199 To try this out, restart the development server with:
1201 DBIC_TRACE=1 script/myapp_server.pl
1203 And enter the following URL into your browser:
1205 http://localhost:3000/books/list_recent_tcp/100
1207 And you should get a list of books added in the last 100 minutes that
1208 contain the string "TCP" in the title. However, if you look at all
1209 books within the last 100 minutes, you should get a longer list
1210 (again, you might have to adjust the number of minutes depending on
1211 how recently you added books to your database):
1213 http://localhost:3000/books/list_recent/100
1215 Take a look at the DBIC_TRACE output in the development server log for
1216 the first URL and you should see something similar to the following:
1218 SELECT me.id, me.title, me.rating, me.created, me.updated FROM book me
1219 WHERE ( ( title LIKE ? AND created > ? ) ): '%TCP%', '2009-05-25 19:09:13'
1221 However, let's not pollute our controller code with this raw "TCP"
1222 query -- it would be cleaner to encapsulate that code in a method on
1223 our ResultSet Class. To do this, open
1224 C<lib/MyApp/Schema/ResultSet/Book.pm> and add the following method:
1228 A predefined search for books with a 'LIKE' search in the string
1233 my ($self, $title_str) = @_;
1235 return $self->search({
1236 title => { 'like' => "%$title_str%" }
1240 We defined the search string as C<$title_str> to make the method more
1241 flexible. Now update the C<list_recent_tcp> method in
1242 C<lib/MyApp/Controller/Books.pm> to match the following (we have
1243 replaced the C<-E<gt>search> line with the C<-E<gt>title_like> line
1244 shown here -- the rest of the method should be the same):
1246 =head2 list_recent_tcp
1248 List recently created books
1252 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1253 my ($self, $c, $mins) = @_;
1255 # Retrieve all of the book records as book model objects and store in the
1256 # stash where they can be accessed by the TT template, but only
1257 # retrieve books created within the last $min number of minutes
1258 # AND that have 'TCP' in the title
1259 $c->stash->{books} = [$c->model('DB::Book')
1260 ->created_after(DateTime->now->subtract(minutes => $mins))
1264 # Set the TT template to use. You will almost always want to do this
1265 # in your action methods (action methods respond to user input in
1266 # your controllers).
1267 $c->stash->{template} = 'books/list.tt2';
1270 Then restart the development server and try out the C<list_recent_tcp>
1271 and C<list_recent> URL as we did above. It should work just the same,
1272 but our code is obviously cleaner and more modular, while also being
1273 more flexible at the same time.
1276 =head2 Adding Methods to Result Classes
1278 In the previous two sections we saw a good example of how we could use
1279 DBIx::Class ResultSet Classes to clean up our code for an entire query
1280 (for example, our "canned searches" that filtered the entire query).
1281 We can do a similar improvement when working with individual rows as
1282 well. Whereas the ResultSet construct is used in DBIC to correspond
1283 to an entire query, the Result Class construct is used to represent a
1284 row. Therefore, we can add row-specific "helper methods" to our Result
1285 Classes stored in C<lib/MyApp/Schema/Result/>. For example, open
1286 C<lib/MyApp/Schema/Result/Author.pm> and add the following method (as
1287 always, it must be above the closing "C<1;>"):
1295 return $self->first_name . ' ' . $self->last_name;
1298 This will allow us to conveniently retrieve both the first and last
1299 name for an author in one shot. Now open C<root/src/books/list.tt2>
1300 and change the definition of C<tt_authors> from this:
1303 [% tt_authors = [ ];
1304 tt_authors.push(author.last_name) FOREACH author = book.authors %]
1310 [% tt_authors = [ ];
1311 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1314 (Only C<author.last_name> was changed to C<author.full_name> -- the
1315 rest of the file should remain the same.)
1317 Now restart the development server and go to the standard book list
1320 http://localhost:3000/books/list
1322 The "Author(s)" column will now contain both the first and last name.
1323 And, because the concatenation logic was encapsulated inside our
1324 Result Class, it keeps the code inside our TT template nice and clean
1325 (remember, we want the templates to be as close to pure HTML markup as
1326 possible). Obviously, this capability becomes even more useful as you
1327 use to to remove even more complicated row-specific logic from your
1331 =head2 Moving Complicated View Code to the Model
1333 The previous section illustrated how we could use a Result Class
1334 method to print the full names of the authors without adding any extra
1335 code to our view, but it still left us with a fairly ugly mess (see
1336 C<root/src/books/list.tt2>):
1340 [% # NOTE: See Chapter 4 for a better way to do this! -%]
1341 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
1342 [% # loop in 'side effect notation' to load just the last names of the -%]
1343 [% # authors into the list. Note that the 'push' TT vmethod does not print -%]
1344 [% # a value, so nothing will be printed here. But, if you have something -%]
1345 [% # in TT that does return a method and you don't want it printed, you -%]
1346 [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to -%]
1347 [% # call it and discard the return value. -%]
1348 [% tt_authors = [ ];
1349 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1350 [% # Now use a TT 'virtual method' to display the author count in parens -%]
1351 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
1352 ([% tt_authors.size | html %])
1353 [% # Use another TT vmethod to join & print the names & comma separators -%]
1354 [% tt_authors.join(', ') | html %]
1358 Let's combine some of the techniques used earlier in this section to
1359 clean this up. First, let's add a method to our Book Result Class to
1360 return the number of authors for a book. Open
1361 C<lib/MyApp/Schema/Result/Book.pm> and add the following method:
1365 Return the number of authors for the current book
1372 # Use the 'many_to_many' relationship to fetch all of the authors for the current
1373 # and the 'count' method in DBIx::Class::ResultSet to get a SQL COUNT
1374 return $self->authors->count;
1377 Next, let's add a method to return a list of authors for a book to the
1378 same C<lib/MyApp/Schema/Result/Book.pm> file:
1382 Return a comma-separated list of authors for the current book
1389 # Loop through all authors for the current book, calling all the 'full_name'
1390 # Result Class method for each
1392 foreach my $author ($self->authors) {
1393 push(@names, $author->full_name);
1396 return join(', ', @names);
1399 This method loops through each author, using the C<full_name> Result
1400 Class method we added to C<lib/MyApp/Schema/Result/Author.pm> in the
1403 Using these two methods, we can simplify our TT code. Open
1404 C<root/src/books/list.tt2> and update the "Author(s)" table cell to
1405 match the following:
1409 [% # Print count and author list using Result Class methods -%]
1410 ([% book.author_count | html %]) [% book.author_list | html %]
1414 Although most of the code we removed comprised comments, the overall
1415 effect is dramatic... because our view code is so simple, we don't
1416 huge comments to clue people in to the gist of our code. The view
1417 code is now self-documenting and readable enough that you could
1418 probably get by with no comments at all. All of the "complex" work is
1419 being done in our Result Class methods (and, because we have broken
1420 the code into nice, modular chucks, the Result Class code is hardly
1421 something you would call complex).
1423 As we saw in this section, always strive to keep your view AND
1424 controller code as simple as possible by pulling code out into your
1425 model objects. Because DBIx::Class can be easily extended in so many
1426 ways, it's an excellent to way accomplish this objective. It will
1427 make your code cleaner, easier to write, less error-prone, and easier
1428 to debug and maintain.
1430 Before you conclude this section, fire up the development server and
1431 hit Refresh in your browser... the output should be the same even
1432 though the backend code has been trimmed down.
1437 Kennedy Clark, C<hkclark@gmail.com>
1439 Please report any errors, issues or suggestions to the author. The
1440 most recent version of the Catalyst Tutorial can be found at
1441 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.
1443 Copyright 2006-2008, Kennedy Clark, under Creative Commons License
1444 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).