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 application
61 L<Chapter 3|Catalyst::Manual::Tutorial::03_MoreCatalystBasics> to add
62 basic support for Create, Read, Update, and Delete (CRUD) of C<Book>
63 objects. Note that the 'list' function in
64 L<Chapter 3|Catalyst::Manual::Tutorial::03_MoreCatalystBasics> already
65 implements the Read portion of CRUD (although Read normally refers to
66 reading a single object; you could implement full Read functionality
67 using the techniques introduced below). This section will focus on the
68 Create and Delete aspects of CRUD. More advanced capabilities,
69 including full Update functionality, will be addressed in
70 L<Chapter 9|Catalyst::Manual::Tutorial::09_AdvancedCRUD>.
72 Although this chapter of the tutorial will show you how to build CRUD
73 functionality yourself, another option is to use a "CRUD builder" type
74 of tool to automate the process. You get less control, but it can be
75 quick and easy. For example, see L<Catalyst::Plugin::AutoCRUD>,
76 L<CatalystX::CRUD>, and L<CatalystX::CRUD::YUI>.
78 You can check out the source code for this example from the Catalyst
79 Subversion repository as per the instructions in
80 L<Catalyst::Manual::Tutorial::01_Intro>.
83 =head1 FORMLESS SUBMISSION
85 Our initial attempt at object creation will utilize the "URL arguments"
86 feature of Catalyst (we will employ the more common form-based
87 submission in the sections that follow).
90 =head2 Include a Create Action in the Books Controller
92 Edit C<lib/MyApp/Controller/Books.pm> and enter the following method:
96 Create a book with the supplied title, rating, and author
100 sub url_create :Local {
101 # In addition to self & context, get the title, rating, &
102 # author_id args from the URL. Note that Catalyst automatically
103 # puts extra information after the "/<controller_name>/<action_name/"
104 # into @_. The args are separated by the '/' char on the URL.
105 my ($self, $c, $title, $rating, $author_id) = @_;
107 # Call create() on the book model object. Pass the table
108 # columns/field values we want to set as hash values
109 my $book = $c->model('DB::Book')->create({
114 # Add a record to the join table for this book, mapping to
116 $book->add_to_book_authors({author_id => $author_id});
117 # Note: Above is a shortcut for this:
118 # $book->create_related('book_authors', {author_id => $author_id});
120 # Assign the Book object to the stash for display and set template
121 $c->stash(book => $book,
122 template => 'books/create_done.tt2');
124 # Disable caching for this page
125 $c->response->header('Cache-Control' => 'no-cache');
128 Notice that Catalyst takes "extra slash-separated information" from the
129 URL and passes it as arguments in C<@_> (as long as the number of
130 arguments is not "fixed" using an attribute like C<:Args(0)>). The
131 C<url_create> action then uses a simple call to the DBIC C<create>
132 method to add the requested information to the database (with a separate
133 call to C<add_to_book_authors> to update the join table). As do
134 virtually all controller methods (at least the ones that directly handle
135 user input), it then sets the template that should handle this request.
137 Also note that we are explicitly setting a C<no-cache> "Cache-Control"
138 header to force browsers using the page to get a fresh copy every time.
139 You could even move this to a C<auto> method in
140 C<lib/MyApp/Controller/Root.pm> and it would automatically get applied
141 to every page in the whole application via a single line of code
142 (remember from Chapter 3, that every C<auto> method gets run in the
143 Controller hierarchy).
146 =head2 Include a Template for the 'url_create' Action:
148 Edit C<root/src/books/create_done.tt2> and then enter:
150 [% # Use the TT Dumper plugin to Data::Dumper variables to the browser -%]
151 [% # Not a good idea for production use, though. :-) 'Indent=1' is -%]
152 [% # optional, but prevents "massive indenting" of deeply nested objects -%]
153 [% USE Dumper(Indent=1) -%]
155 [% # Set the page title. META can 'go back' and set values in templates -%]
156 [% # that have been processed 'before' this template (here it's updating -%]
157 [% # the title in the root/src/wrapper.tt2 wrapper template). Note that -%]
158 [% # META only works on simple/static strings (i.e. there is no variable -%]
159 [% # interpolation -- if you need dynamic/interpolated content in your -%]
160 [% # title, set "$c->stash(title => $something)" in the controller). -%]
161 [% META title = 'Book Created' %]
163 [% # Output information about the record that was added. First title. -%]
164 <p>Added book '[% book.title %]'
166 [% # Then, output the last name of the first author -%]
167 by '[% book.authors.first.last_name %]'
169 [% # Then, output the rating for the book that was added -%]
170 with a rating of [% book.rating %].</p>
172 [% # Provide a link back to the list page. 'c.uri_for' builds -%]
173 [% # a full URI; e.g., 'http://localhost:3000/books/list' -%]
174 <p><a href="[% c.uri_for('/books/list') %]">Return to list</a></p>
176 [% # Try out the TT Dumper (for development only!) -%]
178 Dump of the 'book' variable:
179 [% Dumper.dump(book) %]
182 The TT C<USE> directive allows access to a variety of plugin modules (TT
183 plugins, that is, not Catalyst plugins) to add extra functionality to
184 the base TT capabilities. Here, the plugin allows L<Data::Dumper>
185 "pretty printing" of objects and variables. Other than that, the rest
186 of the code should be familiar from the examples in Chapter 3.
189 =head2 Try the 'url_create' Feature
191 Make sure the development server is running with the "-r" restart
194 $ DBIC_TRACE=1 script/myapp_server.pl -r
196 Note that new path for C</books/url_create> appears in the startup debug
199 Next, use your browser to enter the following URL:
201 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
203 Your browser should display "Added book 'TCPIP_Illustrated_Vol-2' by
204 'Stevens' with a rating of 5." along with a dump of the new book model
205 object as it was returned by DBIC. You should also see the following
206 DBIC debug messages displayed in the development server log messages if
207 you have DBIC_TRACE set:
209 INSERT INTO book (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
210 INSERT INTO book_author (author_id, book_id) VALUES (?, ?): `4', `6'
212 The C<INSERT> statements are obviously adding the book and linking it to
213 the existing record for Richard Stevens. The C<SELECT> statement
214 results from DBIC automatically fetching the book for the
215 C<Dumper.dump(book)>.
217 If you then click the "Return to list" link, you should find that there
218 are now six books shown (if necessary, Shift+Reload or Ctrl+Reload your
219 browser at the C</books/list> page). You should now see the six DBIC
220 debug messages similar to the following (where N=1-6):
222 SELECT author.id, author.first_name, author.last_name
223 FROM book_author me JOIN author author
224 ON author.id = me.author_id WHERE ( me.book_id = ? ): 'N'
227 =head1 CONVERT TO A CHAINED ACTION
229 Although the example above uses the same C<Local> action type for the
230 method that we saw in the previous chapter of the tutorial, there is an
231 alternate approach that allows us to be more specific while also paving
232 the way for more advanced capabilities. Change the method declaration
233 for C<url_create> in C<lib/MyApp/Controller/Books.pm> you entered above
234 to match the following:
236 sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
237 # In addition to self & context, get the title, rating, &
238 # author_id args from the URL. Note that Catalyst automatically
239 # puts the first 3 arguments worth of extra information after the
240 # "/<controller_name>/<action_name/" into @_ because we specified
241 # "Args(3)". The args are separated by the '/' char on the URL.
242 my ($self, $c, $title, $rating, $author_id) = @_;
246 This converts the method to take advantage of the Chained
247 action/dispatch type. Chaining lets you have a single URL automatically
248 dispatch to several controller methods, each of which can have precise
249 control over the number of arguments that it will receive. A chain can
250 essentially be thought of having three parts -- a beginning, a middle,
251 and an end. The bullets below summarize the key points behind each of
252 these parts of a chain:
266 B<Use "C<:Chained('/')>" to start a chain>
270 Get arguments through C<CaptureArgs()>
274 Specify the path to match with C<PathPart()>
287 Link to previous part of the chain with C<:Chained('_name_')>
291 Get arguments through C<CaptureArgs()>
295 Specify the path to match with C<PathPart()>
308 Link to previous part of the chain with C<:Chained('_name_')>
312 B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
316 Specify the path to match with C<PathPart()>
323 In our C<url_create> method above, we have combined all three parts into
324 a single method: C<:Chained('/')> to start the chain,
325 C<:PathPart('books/url_create')> to specify the base URL to match, and
326 C<:Args(3)> to capture exactly three arguments and to end the chain.
328 As we will see shortly, a chain can consist of as many "links" as you
329 wish, with each part capturing some arguments and doing some work along
330 the way. We will continue to use the Chained action type in this
331 chapter of the tutorial and explore slightly more advanced capabilities
332 with the base method and delete feature below. But Chained dispatch is
333 capable of far more. For additional information, see
334 L<Catalyst::Manual::Intro/Action types>,
335 L<Catalyst::DispatchType::Chained>, and the 2006 Advent calendar entry
336 on the subject: L<http://www.catalystframework.org/calendar/2006/10>.
339 =head2 Try the Chained Action
341 If you look back at the development server startup logs from your
342 initial version of the C<url_create> method (the one using the C<:Local>
343 attribute), you will notice that it produced output similar to the
346 [debug] Loaded Path actions:
347 .-------------------------------------+--------------------------------------.
349 +-------------------------------------+--------------------------------------+
352 | /books | /books/index |
353 | /books/list | /books/list |
354 | /books/url_create | /books/url_create |
355 '-------------------------------------+--------------------------------------'
357 When the development server restarts after our conversion to Chained
358 dispatch, the debug output should change to something along the lines of
361 [debug] Loaded Path actions:
362 .-------------------------------------+--------------------------------------.
364 +-------------------------------------+--------------------------------------+
367 | /books | /books/index |
368 | /books/list | /books/list |
369 '-------------------------------------+--------------------------------------'
371 [debug] Loaded Chained actions:
372 .-------------------------------------+--------------------------------------.
373 | Path Spec | Private |
374 +-------------------------------------+--------------------------------------+
375 | /books/url_create/*/*/* | /books/url_create |
376 '-------------------------------------+--------------------------------------'
378 C<url_create> has disappeared from the "Loaded Path actions" section but
379 it now shows up under the newly created "Loaded Chained actions"
380 section. And the "/*/*/*" portion clearly shows our requirement for
383 As with our non-chained version of C<url_create>, use your browser to
384 enter the following URL:
386 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
388 You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
389 'Stevens' with a rating of 5." along with a dump of the new book model
390 object. Click the "Return to list" link, and you should find that there
391 are now seven books shown (two copies of I<TCPIP_Illustrated_Vol-2>).
394 =head2 Refactor to Use a 'base' Method to Start the Chains
396 Let's make a quick update to our initial Chained action to show a little
397 more of the power of chaining. First, open
398 C<lib/MyApp/Controller/Books.pm> in your editor and add the following
403 Can place common logic to start chained dispatch here
407 sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
410 # Store the ResultSet in stash so it's available for other methods
411 $c->stash(resultset => $c->model('DB::Book'));
413 # Print a message to the debug log
414 $c->log->debug('*** INSIDE BASE METHOD ***');
417 Here we print a log message and store the DBIC ResultSet in
418 C<$c-E<gt>stash-E<gt>{resultset}> so that it's automatically available
419 for other actions that chain off C<base>. If your controller always
420 needs a book ID as its first argument, you could have the base method
421 capture that argument (with C<:CaptureArgs(1)>) and use it to pull the
422 book object with C<-E<gt>find($id)> and leave it in the stash for later
423 parts of your chains to then act upon. Because we have several actions
424 that don't need to retrieve a book (such as the C<url_create> we are
425 working with now), we will instead add that functionality to a common
426 C<object> action shortly.
428 As for C<url_create>, let's modify it to first dispatch to C<base>.
429 Open up C<lib/MyApp/Controller/Books.pm> and edit the declaration for
430 C<url_create> to match the following:
432 sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
434 Once you save C<lib/MyApp/Controller/Books.pm>, notice that the
435 development server will restart and our "Loaded Chained actions" section
436 will changed slightly:
438 [debug] Loaded Chained actions:
439 .-------------------------------------+--------------------------------------.
440 | Path Spec | Private |
441 +-------------------------------------+--------------------------------------+
442 | /books/url_create/*/*/* | /books/base (0) |
443 | | => /books/url_create |
444 '-------------------------------------+--------------------------------------'
446 The "Path Spec" is the same, but now it maps to two Private actions as
447 we would expect. The C<base> method is being triggered by the C</books>
448 part of the URL. However, the processing then continues to the
449 C<url_create> method because this method "chained" off C<base> and
450 specified C<:PathPart('url_create')> (note that we could have omitted
451 the "PathPart" here because it matches the name of the method, but we
452 will include it to make the logic as explicit as possible).
454 Once again, enter the following URL into your browser:
456 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
458 The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
459 rating of 5." message and a dump of the new book object should appear.
460 Also notice the extra "INSIDE BASE METHOD" debug message in the
461 development server output from the C<base> method. Click the "Return to
462 list" link, and you should find that there are now eight books shown.
463 (You may have a larger number of books if you repeated any of the
464 "create" actions more than once. Don't worry about it as long as the
465 number of books is appropriate for the number of times you added new
466 books... there should be the original five books added via
467 C<myapp01.sql> plus one additional book for each time you ran one of the
468 url_create variations above.)
471 =head1 MANUALLY BUILDING A CREATE FORM
473 Although the C<url_create> action in the previous step does begin to
474 reveal the power and flexibility of both Catalyst and DBIC, it's
475 obviously not a very realistic example of how users should be expected
476 to enter data. This section begins to address that concern (but just
477 barely, see L<Chapter 9|Catalyst::Manual::Tutorial::09_AdvancedCRUD>
478 for better options for handling web-based forms).
481 =head2 Add Method to Display The Form
483 Edit C<lib/MyApp/Controller/Books.pm> and add the following method:
487 Display form to collect information for book to create
491 sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
494 # Set the TT template to use
495 $c->stash(template => 'books/form_create.tt2');
498 This action simply invokes a view containing a form to create a book.
501 =head2 Add a Template for the Form
503 Open C<root/src/books/form_create.tt2> in your editor and enter:
505 [% META title = 'Manual Form Book Create' -%]
507 <form method="post" action="[% c.uri_for('form_create_do') %]">
509 <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
510 <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
511 <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
513 <input type="submit" name="Submit" value="Submit">
516 Note that we have specified the target of the form data as
517 C<form_create_do>, the method created in the section that follows.
520 =head2 Add a Method to Process Form Values and Update Database
522 Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
523 save the form information to the database:
525 =head2 form_create_do
527 Take information from form and add to database
531 sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
534 # Retrieve the values from the form
535 my $title = $c->request->params->{title} || 'N/A';
536 my $rating = $c->request->params->{rating} || 'N/A';
537 my $author_id = $c->request->params->{author_id} || '1';
540 my $book = $c->model('DB::Book')->create({
544 # Handle relationship with author
545 $book->add_to_book_authors({author_id => $author_id});
546 # Note: Above is a shortcut for this:
547 # $book->create_related('book_authors', {author_id => $author_id});
549 # Store new model object in stash and set template
550 $c->stash(book => $book,
551 template => 'books/create_done.tt2');
555 =head2 Test Out The Form
557 Notice that the server startup log reflects the two new chained methods
560 [debug] Loaded Chained actions:
561 .-------------------------------------+--------------------------------------.
562 | Path Spec | Private |
563 +-------------------------------------+--------------------------------------+
564 | /books/form_create | /books/base (0) |
565 | | => /books/form_create |
566 | /books/form_create_do | /books/base (0) |
567 | | => /books/form_create_do |
568 | /books/url_create/*/*/* | /books/base (0) |
569 | | => /books/url_create |
570 '-------------------------------------+--------------------------------------'
572 Point your browser to L<http://localhost:3000/books/form_create> and
573 enter "TCP/IP Illustrated, Vol 3" for the title, a rating of 5, and an
574 author ID of 4. You should then see the output of the same
575 C<create_done.tt2> template seen in earlier examples. Finally, click
576 "Return to list" to view the full list of books.
578 B<Note:> Having the user enter the primary key ID for the author is
579 obviously crude; we will address this concern with a drop-down list and
580 add validation to our forms in
581 L<Chapter 9|Catalyst::Manual::Tutorial::09_AdvancedCRUD>.
584 =head1 A SIMPLE DELETE FEATURE
586 Turning our attention to the Delete portion of CRUD, this section
587 illustrates some basic techniques that can be used to remove information
591 =head2 Include a Delete Link in the List
593 Edit C<root/src/books/list.tt2> and update it to match the following
594 (two sections have changed: 1) the additional '<th>Links</th>' table
595 header, and 2) the five lines for the Delete link near the bottom):
597 [% # This is a TT comment. -%]
599 [%- # Provide a title -%]
600 [% META title = 'Book List' -%]
602 [% # Note That the '-' at the beginning or end of TT code -%]
603 [% # "chomps" the whitespace/newline at that end of the -%]
604 [% # output (use View Source in browser to see the effect) -%]
606 [% # Some basic HTML with a loop to display books -%]
608 <tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
609 [% # Display each book in a table row %]
610 [% FOREACH book IN books -%]
612 <td>[% book.title %]</td>
613 <td>[% book.rating %]</td>
615 [% # NOTE: See Chapter 4 for a better way to do this! -%]
616 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
617 [% # loop in 'side effect notation' to load just the last names of the -%]
618 [% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
619 [% # a value, so nothing will be printed here. But, if you have something -%]
620 [% # in TT that does return a value and you don't want it printed, you -%]
621 [% # 1) assign it to a bogus value, or -%]
622 [% # 2) use the CALL keyword to call it and discard the return value. -%]
624 tt_authors.push(author.last_name) FOREACH author = book.authors %]
625 [% # Now use a TT 'virtual method' to display the author count in parens -%]
626 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
627 ([% tt_authors.size | html %])
628 [% # Use another TT vmethod to join & print the names & comma separators -%]
629 [% tt_authors.join(', ') | html %]
632 [% # Add a link to delete a book %]
634 c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
640 The additional code is obviously designed to add a new column to the
641 right side of the table with a C<Delete> "button" (for simplicity, links
642 will be used instead of full HTML buttons; but, in practice, anything
643 that modifies data should be handled with a form sending a POST
646 Also notice that we are using a more advanced form of C<uri_for> than we
647 have seen before. Here we use C<$c-E<gt>controller-E<gt>action_for> to
648 automatically generate a URI appropriate for that action based on the
649 method we want to link to while inserting the C<book.id> value into the
650 appropriate place. Now, if you ever change C<:PathPart('delete')> in
651 your controller method to something like C<:PathPart('kill')>, then your
652 links will automatically update without any changes to your .tt2
653 template file. As long as the name of your method does not change
654 (here, "delete"), then your links will still be correct. There are a
655 few shortcuts and options when using C<action_for()>:
661 If you are referring to a method in the current controller, you can use
662 C<$self-E<gt>action_for('_method_name_')>.
666 If you are referring to a method in a different controller, you need to
667 include that controller's name as an argument to C<controller()>, as in
668 C<$c-E<gt>controller('_controller_name_')-E<gt>action_for('_method_name_')>.
672 B<Note:> In practice you should B<never> use a GET request to delete a
673 record -- always use POST for actions that will modify data. We are
674 doing it here for illustrative and simplicity purposes only.
677 =head2 Add a Common Method to Retrieve a Book for the Chain
679 As mentioned earlier, since we have a mixture of actions that operate on
680 a single book ID and others that do not, we should not have C<base>
681 capture the book ID, find the corresponding book in the database and
682 save it in the stash for later links in the chain. However, just
683 because that logic does not belong in C<base> doesn't mean that we can't
684 create another location to centralize the book lookup code. In our
685 case, we will create a method called C<object> that will store the
686 specific book in the stash. Chains that always operate on a single
687 existing book can chain off this method, but methods such as
688 C<url_create> that don't operate on an existing book can chain directly
691 To add the C<object> method, edit C<lib/MyApp/Controller/Books.pm> and
692 add the following code:
696 Fetch the specified book object based on the book ID and store
701 sub object :Chained('base') :PathPart('id') :CaptureArgs(1) {
702 # $id = primary key of book to delete
703 my ($self, $c, $id) = @_;
705 # Find the book object and store it in the stash
706 $c->stash(object => $c->stash->{resultset}->find($id));
708 # Make sure the lookup was successful. You would probably
709 # want to do something like this in a real app:
710 # $c->detach('/error_404') if !$c->stash->{object};
711 die "Book $id not found!" if !$c->stash->{object};
713 # Print a message to the debug log
714 $c->log->debug("*** INSIDE OBJECT METHOD for obj id=$id ***");
717 Now, any other method that chains off C<object> will automatically have
718 the appropriate book waiting for it in C<$c-E<gt>stash-E<gt>{object}>.
721 =head2 Add a Delete Action to the Controller
723 Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
732 sub delete :Chained('object') :PathPart('delete') :Args(0) {
735 # Use the book object saved by 'object' and delete it along
736 # with related 'book_author' entries
737 $c->stash->{object}->delete;
739 # Set a status message to be displayed at the top of the view
740 $c->stash->{status_msg} = "Book deleted.";
742 # Forward to the list action/method in this controller
746 This method first deletes the book object saved by the C<object> method.
747 However, it also removes the corresponding entry from the C<book_author>
748 table with a cascading delete.
750 Then, rather than forwarding to a "delete done" page as we did with the
751 earlier create example, it simply sets the C<status_msg> to display a
752 notification to the user as the normal list view is rendered.
754 The C<delete> action uses the context C<forward> method to return the
755 user to the book list. The C<detach> method could have also been used.
756 Whereas C<forward> I<returns> to the original action once it is
757 completed, C<detach> does I<not> return. Other than that, the two are
761 =head2 Try the Delete Feature
763 Once you save the Books controller, the server should automatically
764 restart. The C<delete> method should now appear in the "Loaded Chained
765 actions" section of the startup debug output:
767 [debug] Loaded Chained actions:
768 .-------------------------------------+--------------------------------------.
769 | Path Spec | Private |
770 +-------------------------------------+--------------------------------------+
771 | /books/id/*/delete | /books/base (0) |
772 | | -> /books/object (1) |
773 | | => /books/delete |
774 | /books/form_create | /books/base (0) |
775 | | => /books/form_create |
776 | /books/form_create_do | /books/base (0) |
777 | | => /books/form_create_do |
778 | /books/url_create/*/*/* | /books/base (0) |
779 | | => /books/url_create |
780 '-------------------------------------+--------------------------------------'
782 Then point your browser to L<http://localhost:3000/books/list> and click
783 the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
784 "Book deleted" status message should display at the top of the page,
785 along with a list of the eight remaining books. You will also see the
786 cascading delete operation via the DBIC_TRACE output:
788 SELECT me.id, me.title, me.rating FROM book me WHERE ( ( me.id = ? ) ): '6'
789 DELETE FROM book WHERE ( id = ? ): '6'
792 =head2 Fixing a Dangerous URL
794 Note the URL in your browser once you have performed the deletion in the
795 prior step -- it is still referencing the delete action:
797 http://localhost:3000/books/id/6/delete
799 What if the user were to press reload with this URL still active? In
800 this case the redundant delete is harmless (although it does generate an
801 exception screen, it doesn't perform any undesirable actions on the
802 application or database), but in other cases this could clearly lead to
805 We can improve the logic by converting to a redirect. Unlike
806 C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform a
807 server-side alteration in the flow of processing, a redirect is a
808 client-side mechanism that causes the browser to issue an entirely new
809 request. As a result, the URL in the browser is updated to match the
810 destination of the redirection URL.
812 To convert the forward used in the previous section to a redirect, open
813 C<lib/MyApp/Controller/Books.pm> and edit the existing C<sub delete>
822 sub delete :Chained('object') :PathPart('delete') :Args(0) {
825 # Use the book object saved by 'object' and delete it along
826 # with related 'book_author' entries
827 $c->stash->{object}->delete;
829 # Set a status message to be displayed at the top of the view
830 $c->stash->{status_msg} = "Book deleted.";
832 # Redirect the user back to the list page. Note the use
833 # of $self->action_for as earlier in this section (BasicCRUD)
834 $c->response->redirect($c->uri_for($self->action_for('list')));
838 =head2 Try the Delete and Redirect Logic
840 Point your browser to L<http://localhost:3000/books/list> (don't just
841 hit "Refresh" in your browser since we left the URL in an invalid state
842 in the previous section!) and delete the first copy of the remaining two
843 "TCPIP_Illustrated_Vol-2" books. The URL in your browser should return
844 to the L<http://localhost:3000/books/list> URL, so that is an
845 improvement, but notice that I<no green "Book deleted" status message is
846 displayed>. Because the stash is reset on every request (and a redirect
847 involves a second request), the C<status_msg> is cleared before it can
851 =head2 Using 'uri_for' to Pass Query Parameters
853 There are several ways to pass information across a redirect. One option
854 is to use the C<flash> technique that we will see in
855 L<Chapter 5|Catalyst::Manual::Tutorial::05_Authentication> of this
856 tutorial; however, here we will pass the information via query
857 parameters on the redirect itself. Open
858 C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
859 method to match the following:
867 sub delete :Chained('object') :PathPart('delete') :Args(0) {
870 # Use the book object saved by 'object' and delete it along
871 # with related 'book_author' entries
872 $c->stash->{object}->delete;
874 # Redirect the user back to the list page with status msg as an arg
875 $c->response->redirect($c->uri_for($self->action_for('list'),
876 {status_msg => "Book deleted."}));
879 This modification simply leverages the ability of C<uri_for> to include
880 an arbitrary number of name/value pairs in a hash reference. Next, we
881 need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
886 [%# Status and error messages %]
887 <span class="message">[%
888 status_msg || c.request.params.status_msg | html %]</span>
889 <span class="error">[% error_msg %]</span>
890 [%# This is where TT will stick all of your template's contents. -%]
892 </div><!-- end content -->
895 Although the sample above only shows the C<content> div, leave the rest
896 of the file intact -- the only change we made to the C<wrapper.tt2> was
897 to add "C<|| c.request.params.status_msg>" to the
898 C<E<lt>span class="message"E<gt>> line.
901 =head2 Try the Delete and Redirect With Query Param Logic
903 Point your browser to L<http://localhost:3000/books/list> (you should
904 now be able to safely hit "refresh" in your browser). Then delete the
905 remaining copy of "TCPIP_Illustrated_Vol-2". The green "Book deleted"
906 status message should return. But notice that you can now hit the
907 "Reload" button in your browser and it just redisplays the book list
908 (and it correctly shows it without the "Book deleted" message on
911 B<NOTE:> Be sure to check out
912 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication> where we
913 use an improved technique that is better suited to your real world
917 =head1 EXPLORING THE POWER OF DBIC
919 In this section we will explore some additional capabilities offered by
920 L<DBIx::Class>. Although these features have relatively little to do
921 with Catalyst per se, you will almost certainly want to take advantage
922 of them in your applications.
925 =head2 Add Datetime Columns to Our Existing Books Table
927 Let's add two columns to our existing C<books> table to track when each
928 book was added and when each book is updated:
931 sqlite> ALTER TABLE book ADD created TIMESTAMP;
932 sqlite> ALTER TABLE book ADD updated TIMESTAMP;
933 sqlite> UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
934 sqlite> SELECT * FROM book;
935 1|CCSP SNRS Exam Certification Guide|5|2010-02-16 04:15:45|2010-02-16 04:15:45
936 2|TCP/IP Illustrated, Volume 1|5|2010-02-16 04:15:45|2010-02-16 04:15:45
937 3|Internetworking with TCP/IP Vol.1|4|2010-02-16 04:15:45|2010-02-16 04:15:45
938 4|Perl Cookbook|5|2010-02-16 04:15:45|2010-02-16 04:15:45
939 5|Designing with Web Standards|5|2010-02-16 04:15:45|2010-02-16 04:15:45
940 9|TCP/IP Illustrated, Vol 3|5|2010-02-16 04:15:45|2010-02-16 04:15:45
944 Here are the commands without the surrounding sqlite3 prompt and output
945 in case you want to cut and paste them as a single block (but still
946 start sqlite3 before you paste these in):
948 ALTER TABLE book ADD created TIMESTAMP;
949 ALTER TABLE book ADD updated TIMESTAMP;
950 UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
953 This will modify the C<books> table to include the two new fields and
954 populate those fields with the current time.
957 =head2 Update DBIx::Class to Automatically Handle the Datetime Columns
959 Next, we should re-run the DBIC helper to update the Result Classes with
962 $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
963 create=static components=TimeStamp dbi:SQLite:myapp.db \
964 on_connect_do="PRAGMA foreign_keys = ON"
965 exists "/root/dev/MyApp/script/../lib/MyApp/Model"
966 exists "/root/dev/MyApp/script/../t"
967 Dumping manual schema for MyApp::Schema to directory /root/dev/MyApp/script/../lib ...
968 Schema dump completed.
969 exists "/root/dev/MyApp/script/../lib/MyApp/Model/DB.pm"
971 Notice that we modified our use of the helper slightly: we told it to
972 include the L<DBIx::Class::TimeStamp> in the C<load_components> line of
975 If you open C<lib/MyApp/Schema/Result/Book.pm> in your editor you should
976 see that the C<created> and C<updated> fields are now included in the
977 call to C<add_columns()>. However, also notice that the C<many_to_many>
978 relationships we manually added below the "C<# DO NOT MODIFY...>" line
979 were automatically preserved.
981 While we C<lib/MyApp/Schema/Result/Book.pm> open, let's update it with
982 some additional information to have DBIC automatically handle the
983 updating of these two fields for us. Insert the following code at the
984 bottom of the file (it B<must> be B<below> the "C<# DO NOT MODIFY...>"
985 line and B<above> the C<1;> on the last line):
988 # Enable automatic date handling
990 __PACKAGE__->add_columns(
992 { data_type => 'timestamp', set_on_create => 1 },
994 { data_type => 'timestamp', set_on_create => 1, set_on_update => 1 },
997 This will override the definition for these fields that Schema::Loader
998 placed at the top of the file. The C<set_on_create> and
999 C<set_on_update> options will cause DBIx::Class to automatically update
1000 the timestamps in these columns whenever a row is created or modified.
1002 B<Note> that adding the lines above will cause the development server to
1003 automatically restart if you are running it with the "-r" option. In
1004 other words, the development server is smart enough to restart not only
1005 for code under the C<MyApp/Controller/>, C<MyApp/Model/>, and
1006 C<MyApp/View/> directories, but also under other directions such as our
1007 "external DBIC model" in C<MyApp/Schema/>. However, also note that it's
1008 smart enough to B<not> restart when you edit your C<.tt2> files under
1011 Then enter the following URL into your web browser:
1013 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
1015 You should get the same "Book Created" screen we saw earlier. However, if
1016 you now use the sqlite3 command-line tool to dump the C<books> table,
1017 you will see that the new book we added has an appropriate date and time
1018 entered for it (see the last line in the listing below):
1020 $ sqlite3 myapp.db "select * from book"
1021 1|CCSP SNRS Exam Certification Guide|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1022 2|TCP/IP Illustrated, Volume 1|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1023 3|Internetworking with TCP/IP Vol.1|4|2010-02-16 04:15:45|2010-02-16 04:15:45
1024 4|Perl Cookbook|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1025 5|Designing with Web Standards|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1026 9|TCP/IP Illustrated, Vol 3|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1027 10|TCPIP_Illustrated_Vol-2|5|2010-02-16 04:18:42|2010-02-16 04:18:42
1029 Notice in the debug log that the SQL DBIC generated has changed to
1030 incorporate the datetime logic:
1032 INSERT INTO book ( created, rating, title, updated ) VALUES ( ?, ?, ?, ? ):
1033 '2010-02-16 04:18:42', '5', 'TCPIP_Illustrated_Vol-2', '2010-02-16 04:18:42'
1034 INSERT INTO book_author ( author_id, book_id ) VALUES ( ?, ? ): '4', '10'
1037 =head2 Create a ResultSet Class
1039 An often overlooked but extremely powerful features of DBIC is that it
1040 allows you to supply your own subclasses of C<DBIx::Class::ResultSet>.
1041 This can be used to pull complex and unsightly "query code" out of your
1042 controllers and encapsulate it in a method of your ResultSet Class.
1043 These "canned queries" in your ResultSet Class can then be invoked via a
1044 single call, resulting in much cleaner and easier to read controller
1045 code (or View code, if that's where you want to call it).
1047 To illustrate the concept with a fairly simple example, let's create a
1048 method that returns books added in the last 10 minutes. Start by making
1049 a directory where DBIx::Class will look for our ResultSet Class:
1051 $ mkdir lib/MyApp/Schema/ResultSet
1053 Then open C<lib/MyApp/Schema/ResultSet/Book.pm> and enter the following:
1055 package MyApp::Schema::ResultSet::Book;
1059 use base 'DBIx::Class::ResultSet';
1061 =head2 created_after
1063 A predefined search for recently added books
1068 my ($self, $datetime) = @_;
1070 my $date_str = $self->result_source->schema->storage
1071 ->datetime_parser->format_datetime($datetime);
1073 return $self->search({
1074 created => { '>' => $date_str }
1080 Then add the following method to the C<lib/MyApp/Controller/Books.pm>:
1084 List recently created books
1088 sub list_recent :Chained('base') :PathPart('list_recent') :Args(1) {
1089 my ($self, $c, $mins) = @_;
1091 # Retrieve all of the book records as book model objects and store in the
1092 # stash where they can be accessed by the TT template, but only
1093 # retrieve books created within the last $min number of minutes
1094 $c->stash(books => [$c->model('DB::Book')
1095 ->created_after(DateTime->now->subtract(minutes => $mins))]);
1097 # Set the TT template to use. You will almost always want to do this
1098 # in your action methods (action methods respond to user input in
1099 # your controllers).
1100 $c->stash(template => 'books/list.tt2');
1103 Now try different values for the "minutes" argument (the final number
1104 value) using the URL C<http://localhost:3000/books/list_recent/_#_> in
1105 your browser. For example, this would list all books added in the last
1108 http://localhost:3000/books/list_recent/15
1110 Depending on how recently you added books, you might want to try a
1111 higher or lower value for the minutes.
1114 =head2 Chaining ResultSets
1116 One of the most helpful and powerful features in C<DBIx::Class> is that
1117 it allows you to "chain together" a series of queries (note that this
1118 has nothing to do with the "Chained Dispatch" for Catalyst that we were
1119 discussing earlier). Because each ResultSet method returns another
1120 ResultSet, you can take an initial query and immediately feed that into
1121 a second query (and so on for as many queries you need). Note that no
1122 matter how many ResultSets you chain together, the database itself will
1123 not be hit until you use a method that attempts to access the data. And,
1124 because this technique carries over to the ResultSet Class feature we
1125 implemented in the previous section for our "canned search", we can
1126 combine the two capabilities. For example, let's add an action to our
1127 C<Books> controller that lists books that are both recent I<and> have
1128 "TCP" in the title. Open up C<lib/MyApp/Controller/Books.pm> and add
1129 the following method:
1131 =head2 list_recent_tcp
1133 List recently created books
1137 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1138 my ($self, $c, $mins) = @_;
1140 # Retrieve all of the book records as book model objects and store in the
1141 # stash where they can be accessed by the TT template, but only
1142 # retrieve books created within the last $min number of minutes
1143 # AND that have 'TCP' in the title
1144 $c->stash(books => [
1145 $c->model('DB::Book')
1146 ->created_after(DateTime->now->subtract(minutes => $mins))
1147 ->search({title => {'like', '%TCP%'}})
1150 # Set the TT template to use. You will almost always want to do this
1151 # in your action methods (action methods respond to user input in
1152 # your controllers).
1153 $c->stash(template => 'books/list.tt2');
1156 To try this out, enter the following URL into your browser:
1158 http://localhost:3000/books/list_recent_tcp/100
1160 And you should get a list of books added in the last 100 minutes that
1161 contain the string "TCP" in the title. However, if you look at all
1162 books within the last 100 minutes, you should get a longer list (again,
1163 you might have to adjust the number of minutes depending on how recently
1164 you added books to your database):
1166 http://localhost:3000/books/list_recent/100
1168 Take a look at the DBIC_TRACE output in the development server log for
1169 the first URL and you should see something similar to the following:
1171 SELECT me.id, me.title, me.rating, me.created, me.updated FROM book me
1172 WHERE ( ( title LIKE ? AND created > ? ) ): '%TCP%', '2010-02-16 02:49:32'
1174 However, let's not pollute our controller code with this raw "TCP" query
1175 -- it would be cleaner to encapsulate that code in a method on our
1176 ResultSet Class. To do this, open C<lib/MyApp/Schema/ResultSet/Book.pm>
1177 and add the following method:
1181 A predefined search for books with a 'LIKE' search in the string
1186 my ($self, $title_str) = @_;
1188 return $self->search({
1189 title => { 'like' => "%$title_str%" }
1193 We defined the search string as C<$title_str> to make the method more
1194 flexible. Now update the C<list_recent_tcp> method in
1195 C<lib/MyApp/Controller/Books.pm> to match the following (we have
1196 replaced the C<-E<gt>search> line with the C<-E<gt>title_like> line
1197 shown here -- the rest of the method should be the same):
1199 =head2 list_recent_tcp
1201 List recently created books
1205 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1206 my ($self, $c, $mins) = @_;
1208 # Retrieve all of the book records as book model objects and store in the
1209 # stash where they can be accessed by the TT template, but only
1210 # retrieve books created within the last $min number of minutes
1211 # AND that have 'TCP' in the title
1212 $c->stash(books => [
1213 $c->model('DB::Book')
1214 ->created_after(DateTime->now->subtract(minutes => $mins))
1218 # Set the TT template to use. You will almost always want to do this
1219 # in your action methods (action methods respond to user input in
1220 # your controllers).
1221 $c->stash(template => 'books/list.tt2');
1224 Try out the C<list_recent_tcp> and C<list_recent> URLs as we did above.
1225 They should work just the same, but our code is obviously cleaner and
1226 more modular, while also being more flexible at the same time.
1229 =head2 Adding Methods to Result Classes
1231 In the previous two sections we saw a good example of how we could use
1232 DBIx::Class ResultSet Classes to clean up our code for an entire query
1233 (for example, our "canned searches" that filtered the entire query). We
1234 can do a similar improvement when working with individual rows as well.
1235 Whereas the ResultSet construct is used in DBIC to correspond to an
1236 entire query, the Result Class construct is used to represent a row.
1237 Therefore, we can add row-specific "helper methods" to our Result
1238 Classes stored in C<lib/MyApp/Schema/Result/>. For example, open
1239 C<lib/MyApp/Schema/Result/Author.pm> and add the following method (as
1240 always, it must be above the closing "C<1;>"):
1243 # Row-level helper methods
1248 return $self->first_name . ' ' . $self->last_name;
1251 This will allow us to conveniently retrieve both the first and last name
1252 for an author in one shot. Now open C<root/src/books/list.tt2> and
1253 change the definition of C<tt_authors> from this:
1256 [% tt_authors = [ ];
1257 tt_authors.push(author.last_name) FOREACH author = book.authors %]
1263 [% tt_authors = [ ];
1264 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1267 (Only C<author.last_name> was changed to C<author.full_name> -- the rest
1268 of the file should remain the same.)
1270 Now go to the standard book list URL:
1272 http://localhost:3000/books/list
1274 The "Author(s)" column will now contain both the first and last name.
1275 And, because the concatenation logic was encapsulated inside our Result
1276 Class, it keeps the code inside our TT template nice and clean
1277 (remember, we want the templates to be as close to pure HTML markup as
1278 possible). Obviously, this capability becomes even more useful as you
1279 use it to remove even more complicated row-specific logic from your
1283 =head2 Moving Complicated View Code to the Model
1285 The previous section illustrated how we could use a Result Class method
1286 to print the full names of the authors without adding any extra code to
1287 our view, but it still left us with a fairly ugly mess (see
1288 C<root/src/books/list.tt2>):
1292 [% # NOTE: See Chapter 4 for a better way to do this! -%]
1293 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
1294 [% # loop in 'side effect notation' to load just the last names of the -%]
1295 [% # authors into the list. Note that the 'push' TT vmethod does not print -%]
1296 [% # a value, so nothing will be printed here. But, if you have something -%]
1297 [% # in TT that does return a method and you don't want it printed, you -%]
1298 [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to -%]
1299 [% # call it and discard the return value. -%]
1300 [% tt_authors = [ ];
1301 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1302 [% # Now use a TT 'virtual method' to display the author count in parens -%]
1303 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
1304 ([% tt_authors.size | html %])
1305 [% # Use another TT vmethod to join & print the names & comma separators -%]
1306 [% tt_authors.join(', ') | html %]
1310 Let's combine some of the techniques used earlier in this section to
1311 clean this up. First, let's add a method to our Book Result Class to
1312 return the number of authors for a book. Open
1313 C<lib/MyApp/Schema/Result/Book.pm> and add the following method:
1317 Return the number of authors for the current book
1324 # Use the 'many_to_many' relationship to fetch all of the authors for the current
1325 # and the 'count' method in DBIx::Class::ResultSet to get a SQL COUNT
1326 return $self->authors->count;
1329 Next, let's add a method to return a list of authors for a book to the
1330 same C<lib/MyApp/Schema/Result/Book.pm> file:
1334 Return a comma-separated list of authors for the current book
1341 # Loop through all authors for the current book, calling all the 'full_name'
1342 # Result Class method for each
1344 foreach my $author ($self->authors) {
1345 push(@names, $author->full_name);
1348 return join(', ', @names);
1351 This method loops through each author, using the C<full_name> Result
1352 Class method we added to C<lib/MyApp/Schema/Result/Author.pm> in the
1355 Using these two methods, we can simplify our TT code. Open
1356 C<root/src/books/list.tt2> and update the "Author(s)" table cell to
1357 match the following:
1361 [% # Print count and author list using Result Class methods -%]
1362 ([% book.author_count | html %]) [% book.author_list | html %]
1366 Although most of the code we removed comprised comments, the overall
1367 effect is dramatic... because our view code is so simple, we don't need
1368 huge comments to clue people in to the gist of our code. The view code
1369 is now self-documenting and readable enough that you could probably get
1370 by with no comments at all. All of the "complex" work is being done in
1371 our Result Class methods (and, because we have broken the code into
1372 nice, modular chunks, the Result Class code is hardly something you
1373 would call complex).
1375 As we saw in this section, always strive to keep your view AND
1376 controller code as simple as possible by pulling code out into your
1377 model objects. Because L<DBIx::Class> can be easily extended in so many
1378 ways, it's an excellent to way accomplish this objective. It will make
1379 your code cleaner, easier to write, less error-prone, and easier to
1382 Before you conclude this section, hit Refresh in your browser... the
1383 output should be the same even though the backend code has been trimmed
1389 Kennedy Clark, C<hkclark@gmail.com>
1391 Feel free to contact the author for any errors or suggestions, but the
1392 best way to report issues is via the CPAN RT Bug system at
1393 <https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.
1395 The most recent version of the Catalyst Tutorial can be found at
1396 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.
1398 Copyright 2006-2010, Kennedy Clark, under the
1399 Creative Commons Attribution Share-Alike License Version 3.0
1400 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).