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
60 created in Chapter 3 to add basic support for Create, Read, Update, and
61 Delete (CRUD) of C<Book> objects. Note that the 'list' function in
62 Chapter 2 already implements the Read portion of CRUD (although Read
63 normally refers to reading a single object; you could implement full
64 Read functionality using the techniques introduced below). This section
65 will focus on the Create and Delete aspects of CRUD. More advanced
66 capabilities, including full Update functionality, will be addressed in
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 can be
72 quick and easy. For example, see L<Catalyst::Plugin::AutoCRUD>,
73 L<CatalystX::CRUD>, and L<CatalystX::CRUD::YUI>.
75 You can check out the source code for this example from the Catalyst
76 Subversion repository as per the instructions in
77 L<Catalyst::Manual::Tutorial::01_Intro>.
80 =head1 FORMLESS SUBMISSION
82 Our initial attempt at object creation will utilize the "URL arguments"
83 feature of Catalyst (we will employ the more common form- based
84 submission in the sections that follow).
87 =head2 Include a Create Action in the Books Controller
89 Edit C<lib/MyApp/Controller/Books.pm> and enter the following method:
93 Create a book with the supplied title, rating, and author
97 sub url_create :Local {
98 # In addition to self & context, get the title, rating, &
99 # author_id args from the URL. Note that Catalyst automatically
100 # puts extra information after the "/<controller_name>/<action_name/"
101 # into @_. The args are separated by the '/' char on the URL.
102 my ($self, $c, $title, $rating, $author_id) = @_;
104 # Call create() on the book model object. Pass the table
105 # columns/field values we want to set as hash values
106 my $book = $c->model('DB::Book')->create({
111 # Add a record to the join table for this book, mapping to
113 $book->add_to_book_authors({author_id => $author_id});
114 # Note: Above is a shortcut for this:
115 # $book->create_related('book_authors', {author_id => $author_id});
117 # Assign the Book object to the stash for display and set template
118 $c->stash(book => $book,
119 template => 'books/create_done.tt2');
122 Notice that Catalyst takes "extra slash-separated information" from the
123 URL and passes it as arguments in C<@_>. The C<url_create> action then
124 uses a simple call to the DBIC C<create> method to add the requested
125 information to the database (with a separate call to
126 C<add_to_book_authors> to update the join table). As do virtually all
127 controller methods (at least the ones that directly handle user input),
128 it then sets the template that should handle this request.
131 =head2 Include a Template for the 'url_create' Action:
133 Edit C<root/src/books/create_done.tt2> and then enter:
135 [% # Use the TT Dumper plugin to Data::Dumper variables to the browser -%]
136 [% # Not a good idea for production use, though. :-) 'Indent=1' is -%]
137 [% # optional, but prevents "massive indenting" of deeply nested objects -%]
138 [% USE Dumper(Indent=1) -%]
140 [% # Set the page title. META can 'go back' and set values in templates -%]
141 [% # that have been processed 'before' this template (here it's for -%]
142 [% # root/lib/site/html and root/lib/site/header). Note that META only -%]
143 [% # works on simple/static strings (i.e. there is no variable -%]
144 [% # interpolation). -%]
145 [% META title = 'Book Created' %]
147 [% # Output information about the record that was added. First title. -%]
148 <p>Added book '[% book.title %]'
150 [% # Output the last name of the first author. -%]
151 by '[% book.authors.first.last_name %]'
153 [% # Output the rating for the book that was added -%]
154 with a rating of [% book.rating %].</p>
156 [% # Provide a link back to the list page -%]
157 [% # 'uri_for()' builds a full URI; e.g., 'http://localhost:3000/books/list' -%]
158 <p><a href="[% c.uri_for('/books/list') %]">Return to list</a></p>
160 [% # Try out the TT Dumper (for development only!) -%]
162 Dump of the 'book' variable:
163 [% Dumper.dump(book) %]
166 The TT C<USE> directive allows access to a variety of plugin modules (TT
167 plugins, that is, not Catalyst plugins) to add extra functionality to
168 the base TT capabilities. Here, the plugin allows L<Data::Dumper>
169 "pretty printing" of objects and variables. Other than that, the rest
170 of the code should be familiar from the examples in Chapter 3.
172 Note: If you are using TT v2.15 you will need to change the code that
173 outputs the "last name for the first author" above to match this:
175 [% authors = book.authors %]
176 by '[% authors.first.last_name IF authors.first;
177 authors.list.first.value.last_name IF ! authors.first %]'
179 to get around an issue in TT v2.15 where blessed hash objects were not
180 handled correctly. But, if you are still using v2.15, it's probably
181 time to upgrade (v2.15 is almost 4 years old). If you are following
182 along in Debian, then you should be on at least v2.20. You can test
183 your version of Template Toolkit with the following:
185 perl -MTemplate -e 'print "$Template::VERSION\n"'
188 =head2 Try the 'url_create' Feature
190 Make sure the development server is running with the "-r" restart
193 $ DBIC_TRACE=1 script/myapp_server.pl -r
195 Note that new path for C</books/url_create> appears in the startup debug
198 Next, use your browser to enter the following URL:
200 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
202 Your browser should display "Added book 'TCPIP_Illustrated_Vol-2' by
203 'Stevens' with a rating of 5." along with a dump of the new book model
204 object as it was returned by DBIC. You should also see the following
205 DBIC debug messages displayed in the development server log messages if
206 you have DBIC_TRACE set:
208 INSERT INTO book (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
209 INSERT INTO book_author (author_id, book_id) VALUES (?, ?): `4', `6'
211 The C<INSERT> statements are obviously adding the book and linking it to
212 the existing record for Richard Stevens. The C<SELECT> statement
213 results from DBIC automatically fetching the book for the
214 C<Dumper.dump(book)>.
216 If you then click the "Return to list" link, you should find that there
217 are now six books shown (if necessary, Shift+Reload or Ctrl+Reload your
218 browser at the C</books/list> page). You should now see the six DBIC
219 debug messages similar to the following (where N=1-6):
221 SELECT author.id, author.first_name, author.last_name
222 FROM book_author me JOIN author author
223 ON author.id = me.author_id WHERE ( me.book_id = ? ): 'N'
226 =head1 CONVERT TO A CHAINED ACTION
228 Although the example above uses the same C<Local> action type for the
229 method that we saw in the previous chapter of the tutorial, there is an
230 alternate approach that allows us to be more specific while also paving
231 the way for more advanced capabilities. Change the method declaration
232 for C<url_create> in C<lib/MyApp/Controller/Books.pm> you entered above
233 to match the following:
235 sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
236 # In addition to self & context, get the title, rating, &
237 # author_id args from the URL. Note that Catalyst automatically
238 # puts the first 3 arguments worth of extra information after the
239 # "/<controller_name>/<action_name/" into @_ because we specified
240 # "Args(3)". The args are separated by the '/' char on the URL.
241 my ($self, $c, $title, $rating, $author_id) = @_;
245 This converts the method to take advantage of the Chained
246 action/dispatch type. Chaining lets you have a single URL automatically
247 dispatch to several controller methods, each of which can have precise
248 control over the number of arguments that it will receive. A chain can
249 essentially be thought of having three parts -- a beginning, a middle,
250 and an end. The bullets below summarize the key points behind each of
251 these parts of a chain:
265 B<Use "C<:Chained('/')>" to start a chain>
269 Get arguments through C<CaptureArgs()>
273 Specify the path to match with C<PathPart()>
286 Link to previous part of the chain with C<:Chained('_name_')>
290 Get arguments through C<CaptureArgs()>
294 Specify the path to match with C<PathPart()>
307 Link to previous part of the chain with C<:Chained('_name_')>
311 B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
315 Specify the path to match with C<PathPart()>
322 In our C<url_create> method above, we have combined all three parts into
323 a single method: C<:Chained('/')> to start the chain,
324 C<:PathPart('books/url_create')> to specify the base URL to match, and
325 C<:Args(3)> to capture exactly three arguments and to end the chain.
327 As we will see shortly, a chain can consist of as many "links" as you
328 wish, with each part capturing some arguments and doing some work along
329 the way. We will continue to use the Chained action type in this
330 chapter of the tutorial and explore slightly more advanced capabilities
331 with the base method and delete feature below. But Chained dispatch is
332 capable of far more. For additional information, see
333 L<Catalyst::Manual::Intro/Action types>,
334 L<Catalyst::DispatchType::Chained>, and the 2006 Advent calendar entry
335 on the subject: L<http://www.catalystframework.org/calendar/2006/10>.
338 =head2 Try the Chained Action
340 If you look back at the development server startup logs from your
341 initial version of the C<url_create> method (the one using the C<:Local>
342 attribute), you will notice that it produced output similar to the
345 [debug] Loaded Path actions:
346 .-------------------------------------+--------------------------------------.
348 +-------------------------------------+--------------------------------------+
351 | /books | /books/index |
352 | /books/list | /books/list |
353 | /books/url_create | /books/url_create |
354 '-------------------------------------+--------------------------------------'
356 When the development server restarts, the debug output should change to
357 something along the lines of the following:
359 [debug] Loaded Path actions:
360 .-------------------------------------+--------------------------------------.
362 +-------------------------------------+--------------------------------------+
365 | /books | /books/index |
366 | /books/list | /books/list |
367 '-------------------------------------+--------------------------------------'
369 [debug] Loaded Chained actions:
370 .-------------------------------------+--------------------------------------.
371 | Path Spec | Private |
372 +-------------------------------------+--------------------------------------+
373 | /books/url_create/*/*/* | /books/url_create |
374 '-------------------------------------+--------------------------------------'
376 C<url_create> has disappeared from the "Loaded Path actions" section but
377 it now shows up under the newly created "Loaded Chained actions"
378 section. And the "/*/*/*" portion clearly shows our requirement for
381 As with our non-chained version of C<url_create>, use your browser to
382 enter the following URL:
384 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
386 You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
387 'Stevens' with a rating of 5." along with a dump of the new book model
388 object. Click the "Return to list" link, and you should find that there
389 are now seven books shown (two copies of I<TCPIP_Illustrated_Vol-2>).
392 =head2 Refactor to Use a 'base' Method to Start the Chains
394 Let's make a quick update to our initial Chained action to show a little
395 more of the power of chaining. First, open
396 C<lib/MyApp/Controller/Books.pm> in your editor and add the following
401 Can place common logic to start chained dispatch here
405 sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
408 # Store the ResultSet in stash so it's available for other methods
409 $c->stash(resultset => $c->model('DB::Book'));
411 # Print a message to the debug log
412 $c->log->debug('*** INSIDE BASE METHOD ***');
415 Here we print a log message and store the DBIC ResultSet in
416 C<$c-E<gt>stash-E<gt>{resultset}> so that it's automatically available
417 for other actions that chain off C<base>. If your controller always
418 needs a book ID as its first argument, you could have the base method
419 capture that argument (with C<:CaptureArgs(1)>) and use it to pull the
420 book object with C<-E<gt>find($id)> and leave it in the stash for later
421 parts of your chains to then act upon. Because we have several actions
422 that don't need to retrieve a book (such as the C<url_create> we are
423 working with now), we will instead add that functionality to a common
424 C<object> action shortly.
426 As for C<url_create>, let's modify it to first dispatch to C<base>.
427 Open up C<lib/MyApp/Controller/Books.pm> and edit the declaration for
428 C<url_create> to match the following:
430 sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
432 Once you save C<lib/MyApp/Controller/Books.pm>, notice that the
433 development server will restart and our "Loaded Chained actions" section
434 will changed slightly:
436 [debug] Loaded Chained actions:
437 .-------------------------------------+--------------------------------------.
438 | Path Spec | Private |
439 +-------------------------------------+--------------------------------------+
440 | /books/url_create/*/*/* | /books/base (0) |
441 | | => /books/url_create |
442 '-------------------------------------+--------------------------------------'
444 The "Path Spec" is the same, but now it maps to two Private actions as
445 we would expect. The C<base> method is being triggered by the C</books>
446 part of the URL. However, the processing then continues to the
447 C<url_create> method because this method "chained" off C<base> and
448 specified C<:PathPart('url_create')> (note that we could have omitted
449 the "PathPart" here because it matches the name of the method, but we
450 will include it to make the logic as explicit as possible).
452 Once again, enter the following URL into your browser:
454 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
456 The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
457 rating of 5." message and a dump of the new book object should appear.
458 Also notice the extra "INSIDE BASE METHOD" debug message in the
459 development server output from the C<base> method. Click the "Return to
460 list" link, and you should find that there are now eight books shown.
461 (You may have a larger number of books if you repeated any of the
462 "create" actions more than once. Don't worry about it as long as the
463 number of books is appropriate for the number of times you added new
464 books... there should be the original five books added via
465 C<myapp01.sql> plus one additional book for each time you ran one of the
466 url_create variations above.)
469 =head1 MANUALLY BUILDING A CREATE FORM
471 Although the C<url_create> action in the previous step does begin to
472 reveal the power and flexibility of both Catalyst and DBIC, it's
473 obviously not a very realistic example of how users should be expected
474 to enter data. This section begins to address that concern.
477 =head2 Add Method to Display The Form
479 Edit C<lib/MyApp/Controller/Books.pm> and add the following method:
483 Display form to collect information for book to create
487 sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
490 # Set the TT template to use
491 $c->stash(template => 'books/form_create.tt2');
494 This action simply invokes a view containing a form to create a book.
497 =head2 Add a Template for the Form
499 Open C<root/src/books/form_create.tt2> in your editor and enter:
501 [% META title = 'Manual Form Book Create' -%]
503 <form method="post" action="[% c.uri_for('form_create_do') %]">
505 <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
506 <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
507 <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
509 <input type="submit" name="Submit" value="Submit">
512 Note that we have specified the target of the form data as
513 C<form_create_do>, the method created in the section that follows.
516 =head2 Add a Method to Process Form Values and Update Database
518 Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
519 save the form information to the database:
521 =head2 form_create_do
523 Take information from form and add to database
527 sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
530 # Retrieve the values from the form
531 my $title = $c->request->params->{title} || 'N/A';
532 my $rating = $c->request->params->{rating} || 'N/A';
533 my $author_id = $c->request->params->{author_id} || '1';
536 my $book = $c->model('DB::Book')->create({
540 # Handle relationship with author
541 $book->add_to_book_authors({author_id => $author_id});
542 # Note: Above is a shortcut for this:
543 # $book->create_related('book_authors', {author_id => $author_id});
545 # Avoid Data::Dumper issue mentioned earlier
546 # You can probably omit this
547 $Data::Dumper::Useperl = 1;
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 Chapter 9.
583 =head1 A SIMPLE DELETE FEATURE
585 Turning our attention to the Delete portion of CRUD, this section
586 illustrates some basic techniques that can be used to remove information
590 =head2 Include a Delete Link in the List
592 Edit C<root/src/books/list.tt2> and update it to match the following
593 (two sections have changed: 1) the additional '<th>Links</th>' table
594 header, and 2) the four lines for the Delete link near the bottom):
596 [% # This is a TT comment. The '-' at the end "chomps" the newline. You won't -%]
597 [% # see this "chomping" in your browser because HTML ignores blank lines, but -%]
598 [% # it WILL eliminate a blank line if you view the HTML source. It's purely -%]
599 [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
601 [% # Provide a title -%]
602 [% META title = 'Book List' -%]
605 <tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
606 [% # Display each book in a table row %]
607 [% FOREACH book IN books -%]
609 <td>[% book.title %]</td>
610 <td>[% book.rating %]</td>
612 [% # NOTE: See "Exploring The Power of DBIC" for a better way to do this! -%]
613 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
614 [% # loop in 'side effect notation' to load just the last names of the -%]
615 [% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
616 [% # a value, so nothing will be printed here. But, if you have something -%]
617 [% # in TT that does return a value and you don't want it printed, you can -%]
618 [% # 1) assign it to a bogus value, or -%]
619 [% # 2) use the CALL keyword to call it and discard the return value. -%]
621 tt_authors.push(author.last_name) FOREACH author = book.authors %]
622 [% # Now use a TT 'virtual method' to display the author count in parens -%]
623 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
624 ([% tt_authors.size | html %])
625 [% # Use another TT vmethod to join & print the names & comma separators -%]
626 [% tt_authors.join(', ') | html %]
629 [% # Add a link to delete a book %]
630 <a href="[% c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
636 The additional code is obviously designed to add a new column to the
637 right side of the table with a C<Delete> "button" (for simplicity, links
638 will be used instead of full HTML buttons; in practice, anything that
639 modifies data should be handled with a form sending a POST request).
641 Also notice that we are using a more advanced form of C<uri_for> than we
642 have seen before. Here we use C<$c-E<gt>controller-E<gt>action_for> to
643 automatically generate a URI appropriate for that action based on the
644 method we want to link to while inserting the C<book.id> value into the
645 appropriate place. Now, if you ever change C<:PathPart('delete')> in
646 your controller method to C<:PathPart('kill')>, then your links will
647 automatically update without any changes to your .tt2 template file. As
648 long as the name of your method does not change (here, "delete"), then
649 your links will still be correct. There are a few shortcuts and options
650 when using C<action_for()>:
656 If you are referring to a method in the current controller, you can use
657 C<$self-E<gt>action_for('_method_name_')>.
661 If you are referring to a method in a different controller, you need to
662 include that controller's name as an argument to C<controller()>, as in
663 C<$c-E<gt>controller('_controller_name_')-E<gt>action_for('_method_name_')>.
667 B<Note:> In practice you should B<never> use a GET request to delete a
668 record -- always use POST for actions that will modify data. We are
669 doing it here for illustrative and simplicity purposes only.
672 =head2 Add a Common Method to Retrieve a Book for the Chain
674 As mentioned earlier, since we have a mixture of actions that operate on
675 a single book ID and others that do not, we should not have C<base>
676 capture the book ID, find the corresponding book in the database and
677 save it in the stash for later links in the chain. However, just
678 because that logic does not belong in C<base> doesn't mean that we can't
679 create another location to centralize the book lookup code. In our
680 case, we will create a method called C<object> that will store the
681 specific book in the stash. Chains that always operate on a single
682 existing book can chain off this method, but methods such as
683 C<url_create> that don't operate on an existing book can chain directly
686 To add the C<object> method, edit C<lib/MyApp/Controller/Books.pm> and
687 add the following code:
691 Fetch the specified book object based on the book ID and store
696 sub object :Chained('base') :PathPart('id') :CaptureArgs(1) {
697 # $id = primary key of book to delete
698 my ($self, $c, $id) = @_;
700 # Find the book object and store it in the stash
701 $c->stash(object => $c->stash->{resultset}->find($id));
703 # Make sure the lookup was successful. You would probably
704 # want to do something like this in a real app:
705 # $c->detach('/error_404') if !$c->stash->{object};
706 die "Book $id not found!" if !$c->stash->{object};
708 # Print a message to the debug log
709 $c->log->debug("*** INSIDE OBJECT METHOD for obj id=$id ***");
712 Now, any other method that chains off C<object> will automatically have
713 the appropriate book waiting for it in C<$c-E<gt>stash-E<gt>{object}>.
716 =head2 Add a Delete Action to the Controller
718 Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
727 sub delete :Chained('object') :PathPart('delete') :Args(0) {
730 # Use the book object saved by 'object' and delete it along
731 # with related 'book_author' entries
732 $c->stash->{object}->delete;
734 # Set a status message to be displayed at the top of the view
735 $c->stash->{status_msg} = "Book deleted.";
737 # Forward to the list action/method in this controller
741 This method first deletes the book object saved by the C<object> method.
742 However, it also removes the corresponding entry from the C<book_author>
743 table with a cascading delete.
745 Then, rather than forwarding to a "delete done" page as we did with the
746 earlier create example, it simply sets the C<status_msg> to display a
747 notification to the user as the normal list view is rendered.
749 The C<delete> action uses the context C<forward> method to return the
750 user to the book list. The C<detach> method could have also been used.
751 Whereas C<forward> I<returns> to the original action once it is
752 completed, C<detach> does I<not> return. Other than that, the two are
756 =head2 Try the Delete Feature
758 Once you save the Books controller, the server should automatically
759 restart. The C<delete> method should now appear in the "Loaded Chained
760 actions" section of the startup debug output:
762 [debug] Loaded Chained actions:
763 .-------------------------------------+--------------------------------------.
764 | Path Spec | Private |
765 +-------------------------------------+--------------------------------------+
766 | /books/id/*/delete | /books/base (0) |
767 | | -> /books/object (1) |
768 | | => /books/delete |
769 | /books/form_create | /books/base (0) |
770 | | => /books/form_create |
771 | /books/form_create_do | /books/base (0) |
772 | | => /books/form_create_do |
773 | /books/url_create/*/*/* | /books/base (0) |
774 | | => /books/url_create |
775 '-------------------------------------+--------------------------------------'
777 Then point your browser to L<http://localhost:3000/books/list> and click
778 the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
779 "Book deleted" status message should display at the top of the page,
780 along with a list of the eight remaining books. You will also see the
781 cascading delete operation via the DBIC_TRACE output:
783 SELECT me.id, me.title, me.rating FROM book me WHERE ( ( me.id = ? ) ): '6'
784 DELETE FROM book WHERE ( id = ? ): '6'
785 SELECT me.book_id, me.author_id FROM book_author me WHERE ( me.book_id = ? ): '6'
786 DELETE FROM book_author WHERE ( author_id = ? AND book_id = ? ): '4', '6'
789 =head2 Fixing a Dangerous URL
791 Note the URL in your browser once you have performed the deletion in the
792 prior step -- it is still referencing the delete action:
794 http://localhost:3000/books/id/6/delete
796 What if the user were to press reload with this URL still active? In
797 this case the redundant delete is harmless (although it does generate an
798 exception screen, it doesn't perform any undesirable actions on the
799 application or database), but in other cases this could clearly be
802 We can improve the logic by converting to a redirect. Unlike
803 C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform a
804 server-side alteration in the flow of processing, a redirect is a
805 client-side mechanism that causes the browser to issue an entirely new
806 request. As a result, the URL in the browser is updated to match the
807 destination of the redirection URL.
809 To convert the forward used in the previous section to a redirect, open
810 C<lib/MyApp/Controller/Books.pm> and edit the existing C<sub delete>
819 sub delete :Chained('object') :PathPart('delete') :Args(0) {
822 # Use the book object saved by 'object' and delete it along
823 # with related 'book_author' entries
824 $c->stash->{object}->delete;
826 # Set a status message to be displayed at the top of the view
827 $c->stash->{status_msg} = "Book deleted.";
829 # Redirect the user back to the list page. Note the use
830 # of $self->action_for as earlier in this section (BasicCRUD)
831 $c->response->redirect($c->uri_for($self->action_for('list')));
835 =head2 Try the Delete and Redirect Logic
837 Point your browser to L<http://localhost:3000/books/list> (don't just
838 hit "Refresh" in your browser since we left the URL in an invalid state
839 in the previous section!) and delete the first copy of the remaining two
840 "TCPIP_Illustrated_Vol-2" books. The URL in your browser should return
841 to the L<http://localhost:3000/books/list> URL, so that is an
842 improvement, but notice that I<no green "Book deleted" status message is
843 displayed>. Because the stash is reset on every request (and a redirect
844 involves a second request), the C<status_msg> is cleared before it can
848 =head2 Using 'uri_for' to Pass Query Parameters
850 There are several ways to pass information across a redirect. One option
851 is to use the C<flash> technique that we will see in Chapter 5 of this
852 tutorial; however, here we will pass the information via query
853 parameters on the redirect itself. Open
854 C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
855 method to match the following:
863 sub delete :Chained('object') :PathPart('delete') :Args(0) {
866 # Use the book object saved by 'object' and delete it along
867 # with related 'book_author' entries
868 $c->stash->{object}->delete;
870 # Redirect the user back to the list page with status msg as an arg
871 $c->response->redirect($c->uri_for($self->action_for('list'),
872 {status_msg => "Book deleted."}));
875 This modification simply leverages the ability of C<uri_for> to include
876 an arbitrary number of name/value pairs in a hash reference. Next, we
877 need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
882 [%# Status and error messages %]
883 <span class="message">[%
884 status_msg || c.request.params.status_msg | html %]</span>
885 <span class="error">[% error_msg %]</span>
886 [%# This is where TT will stick all of your template's contents. -%]
888 </div><!-- end content -->
891 Although the sample above only shows the C<content> div, leave the rest
892 of the file intact -- the only change we made to the C<wrapper.tt2> was
893 to add "C<|| c.request.params.status_msg>" to the C<E<lt>span
894 class="message"E<gt>> line.
897 =head2 Try the Delete and Redirect With Query Param Logic
899 Point your browser to L<http://localhost:3000/books/list> (you should
900 now be able to safely hit "refresh" in your browser). Then delete the
901 remaining copy of "TCPIP_Illustrated_Vol-2". The green "Book deleted"
902 status message should return. But notice that you can now hit the
903 "Reload" button in your browser and it just redisplays the book list
904 (and it correctly shows it without the "Book deleted" message on
907 B<NOTE:> Another popular method for maintaining server-side information
908 across a redirect is to use the C<flash> technique we discuss in the
909 next chapter of the tutorial,
910 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>. While
911 C<flash> is a "slicker" mechanism in that it's all handled by the server
912 and doesn't "pollute" your URLs, B<it is important to note that C<flash>
913 can lead to situations where the wrong information shows up in the wrong
914 browser window if the user has multiple windows or browser tabs open>.
915 For example, Window A causes something to be placed in the stash, but
916 before that window performs a redirect, Window B makes a request to the
917 server and gets the status information that should really go to Window
918 A. For this reason, you may wish to use the "query param" technique
919 shown here in your applications.
922 =head1 EXPLORING THE POWER OF DBIC
924 In this section we will explore some additional capabilities offered by
925 DBIx::Class. Although these features have relatively little to do with
926 Catalyst per se, you will almost certainly want to take advantage of
927 them in your applications.
930 =head2 Add Datetime Columns to Our Existing Books Table
932 Let's add two columns to our existing C<books> table to track when each
933 book was added and when each book is updated:
936 sqlite> ALTER TABLE book ADD created TIMESTAMP;
937 sqlite> ALTER TABLE book ADD updated TIMESTAMP;
938 sqlite> UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
939 sqlite> SELECT * FROM book;
940 1|CCSP SNRS Exam Certification Guide|5|2010-02-16 04:15:45|2010-02-16 04:15:45
941 2|TCP/IP Illustrated, Volume 1|5|2010-02-16 04:15:45|2010-02-16 04:15:45
942 3|Internetworking with TCP/IP Vol.1|4|2010-02-16 04:15:45|2010-02-16 04:15:45
943 4|Perl Cookbook|5|2010-02-16 04:15:45|2010-02-16 04:15:45
944 5|Designing with Web Standards|5|2010-02-16 04:15:45|2010-02-16 04:15:45
945 9|TCP/IP Illustrated, Vol 3|5|2010-02-16 04:15:45|2010-02-16 04:15:45
949 This will modify the C<books> table to include the two new fields and
950 populate those fields with the current time.
953 =head2 Update DBIx::Class to Automatically Handle the Datetime Columns
955 Next, we should re-run the DBIC helper to update the Result Classes with
958 $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
959 create=static components=TimeStamp dbi:SQLite:myapp.db \
960 on_connect_do="PRAGMA foreign_keys = ON"
961 exists "/root/dev/MyApp/script/../lib/MyApp/Model"
962 exists "/root/dev/MyApp/script/../t"
963 Dumping manual schema for MyApp::Schema to directory /root/dev/MyApp/script/../lib ...
964 Schema dump completed.
965 exists "/root/dev/MyApp/script/../lib/MyApp/Model/DB.pm"
967 Notice that we modified our use of the helper slightly: we told it to
968 include the L<DBIx::Class::TimeStamp> in the C<load_components> line of
971 If you open C<lib/MyApp/Schema/Result/Book.pm> in your editor you should
972 see that the C<created> and C<updated> fields are now included in the
973 call to C<add_columns()>. However, also notice that the C<many_to_many>
974 relationships we manually added below the "C<# DO NOT MODIFY...>" line
975 were automatically preserved.
977 While we have this file open, let's update it with some additional
978 information to have DBIC automatically handle the updating of these two
979 fields for us. Insert the following code at the bottom of the file (it
980 B<must> be B<below> the "C<# DO NOT MODIFY...>" line and B<above> the
981 C<1;> on the last line):
984 # Enable automatic date handling
986 __PACKAGE__->add_columns(
988 { data_type => 'timestamp', set_on_create => 1 },
990 { data_type => 'timestamp', set_on_create => 1, set_on_update => 1 },
993 This will override the definition for these fields that Schema::Loader
994 placed at the top of the file. The C<set_on_create> and
995 C<set_on_update> options will cause DBIx::Class to automatically update
996 the timestamps in these columns whenever a row is created or modified.
998 Then enter the following URL into your web browser:
1000 http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
1002 You should get the same "Book Created" screen we saw above. However, if
1003 you now use the sqlite3 command-line tool to dump the C<books> table,
1004 you will see that the new book we added has an appropriate date and time
1005 entered for it (see the last line in the listing below):
1007 $ sqlite3 myapp.db "select * from book"
1008 1|CCSP SNRS Exam Certification Guide|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1009 2|TCP/IP Illustrated, Volume 1|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1010 3|Internetworking with TCP/IP Vol.1|4|2010-02-16 04:15:45|2010-02-16 04:15:45
1011 4|Perl Cookbook|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1012 5|Designing with Web Standards|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1013 9|TCP/IP Illustrated, Vol 3|5|2010-02-16 04:15:45|2010-02-16 04:15:45
1014 10|TCPIP_Illustrated_Vol-2|5|2010-02-16 04:18:42|2010-02-16 04:18:42
1017 Notice in the debug log that the SQL DBIC generated has changed to
1018 incorporate the datetime logic:
1020 INSERT INTO book ( created, rating, title, updated ) VALUES ( ?, ?, ?, ? ):
1021 '2010-02-16 04:18:42', '5', 'TCPIP_Illustrated_Vol-2', '2010-02-16 04:18:42'
1022 INSERT INTO book_author ( author_id, book_id ) VALUES ( ?, ? ): '4', '10'
1025 =head2 Create a ResultSet Class
1027 An often overlooked but extremely powerful features of DBIC is that it
1028 allows you to supply your own subclasses of C<DBIx::Class::ResultSet>.
1029 It allows you to pull complex and unsightly "query code" out of your
1030 controllers and encapsulate it in a method of your ResultSet Class.
1031 These "canned queries" in your ResultSet Class can then be invoked via a
1032 single call, resulting in much cleaner and easier to read controller
1035 To illustrate the concept with a fairly simple example, let's create a
1036 method that returns books added in the last 10 minutes. Start by making
1037 a directory where DBIx::Class will look for our ResultSet Class:
1039 $ mkdir lib/MyApp/Schema/ResultSet
1041 Then open C<lib/MyApp/Schema/ResultSet/Book.pm> and enter the following:
1043 package MyApp::Schema::ResultSet::Book;
1047 use base 'DBIx::Class::ResultSet';
1049 =head2 created_after
1051 A predefined search for recently added books
1056 my ($self, $datetime) = @_;
1058 my $date_str = $self->result_source->schema->storage
1059 ->datetime_parser->format_datetime($datetime);
1061 return $self->search({
1062 created => { '>' => $date_str }
1068 Then add the following method to the C<lib/MyApp/Controller/Books.pm>:
1072 List recently created books
1076 sub list_recent :Chained('base') :PathPart('list_recent') :Args(1) {
1077 my ($self, $c, $mins) = @_;
1079 # Retrieve all of the book records as book model objects and store in the
1080 # stash where they can be accessed by the TT template, but only
1081 # retrieve books created within the last $min number of minutes
1082 $c->stash(books => [$c->model('DB::Book')
1083 ->created_after(DateTime->now->subtract(minutes => $mins))]);
1085 # Set the TT template to use. You will almost always want to do this
1086 # in your action methods (action methods respond to user input in
1087 # your controllers).
1088 $c->stash(template => 'books/list.tt2');
1091 Now try different values for the "minutes" argument (the final number
1092 value) using the URL C<http://localhost:3000/books/list_recent/_#_> in
1093 your browser. For example, this would list all books added in the last
1096 http://localhost:3000/books/list_recent/15
1098 Depending on how recently you added books, you might want to try a
1099 higher or lower value for the minutes.
1102 =head2 Chaining ResultSets
1104 One of the most helpful and powerful features in DBIx::Class is that it
1105 allows you to "chain together" a series of queries (note that this has
1106 nothing to do with the "Chained Dispatch" for Catalyst that we were
1107 discussing above). Because each ResultSet returns another ResultSet,
1108 you can take an initial query and immediately feed that into a second
1109 query (and so on for as many queries you need). Note that no matter how
1110 many ResultSets you chain together, the database itself will not be hit
1111 until you use a method that attempts to access the data. And, because
1112 this technique carries over to the ResultSet Class feature we
1113 implemented in the previous section for our "canned search", we can
1114 combine the two capabilities. For example, let's add an action to our
1115 C<Books> controller that lists books that are both recent I<and> have
1116 "TCP" in the title. Open up C<lib/MyApp/Controller/Books.pm> and add
1117 the following method:
1119 =head2 list_recent_tcp
1121 List recently created books
1125 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1126 my ($self, $c, $mins) = @_;
1128 # Retrieve all of the book records as book model objects and store in the
1129 # stash where they can be accessed by the TT template, but only
1130 # retrieve books created within the last $min number of minutes
1131 # AND that have 'TCP' in the title
1132 $c->stash(books => [$c->model('DB::Book')
1133 ->created_after(DateTime->now->subtract(minutes => $mins))
1134 ->search({title => {'like', '%TCP%'}})
1137 # Set the TT template to use. You will almost always want to do this
1138 # in your action methods (action methods respond to user input in
1139 # your controllers).
1140 $c->stash(template => 'books/list.tt2');
1143 To try this out, enter the following URL into your browser:
1145 http://localhost:3000/books/list_recent_tcp/100
1147 And you should get a list of books added in the last 100 minutes that
1148 contain the string "TCP" in the title. However, if you look at all
1149 books within the last 100 minutes, you should get a longer list (again,
1150 you might have to adjust the number of minutes depending on how recently
1151 you added books to your database):
1153 http://localhost:3000/books/list_recent/100
1155 Take a look at the DBIC_TRACE output in the development server log for
1156 the first URL and you should see something similar to the following:
1158 SELECT me.id, me.title, me.rating, me.created, me.updated FROM book me
1159 WHERE ( ( title LIKE ? AND created > ? ) ): '%TCP%', '2010-02-16 02:49:32'
1161 However, let's not pollute our controller code with this raw "TCP" query
1162 -- it would be cleaner to encapsulate that code in a method on our
1163 ResultSet Class. To do this, open C<lib/MyApp/Schema/ResultSet/Book.pm>
1164 and add the following method:
1168 A predefined search for books with a 'LIKE' search in the string
1173 my ($self, $title_str) = @_;
1175 return $self->search({
1176 title => { 'like' => "%$title_str%" }
1180 We defined the search string as C<$title_str> to make the method more
1181 flexible. Now update the C<list_recent_tcp> method in
1182 C<lib/MyApp/Controller/Books.pm> to match the following (we have
1183 replaced the C<-E<gt>search> line with the C<-E<gt>title_like> line
1184 shown here -- the rest of the method should be the same):
1186 =head2 list_recent_tcp
1188 List recently created books
1192 sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
1193 my ($self, $c, $mins) = @_;
1195 # Retrieve all of the book records as book model objects and store in the
1196 # stash where they can be accessed by the TT template, but only
1197 # retrieve books created within the last $min number of minutes
1198 # AND that have 'TCP' in the title
1199 $c->stash(books => [$c->model('DB::Book')
1200 ->created_after(DateTime->now->subtract(minutes => $mins))
1204 # Set the TT template to use. You will almost always want to do this
1205 # in your action methods (action methods respond to user input in
1206 # your controllers).
1207 $c->stash(template => 'books/list.tt2');
1210 Try out the C<list_recent_tcp> and C<list_recent> URLs as we did above.
1211 They should work just the same, but our code is obviously cleaner and
1212 more modular, while also being more flexible at the same time.
1215 =head2 Adding Methods to Result Classes
1217 In the previous two sections we saw a good example of how we could use
1218 DBIx::Class ResultSet Classes to clean up our code for an entire query
1219 (for example, our "canned searches" that filtered the entire query). We
1220 can do a similar improvement when working with individual rows as well.
1221 Whereas the ResultSet construct is used in DBIC to correspond to an
1222 entire query, the Result Class construct is used to represent a row.
1223 Therefore, we can add row-specific "helper methods" to our Result
1224 Classes stored in C<lib/MyApp/Schema/Result/>. For example, open
1225 C<lib/MyApp/Schema/Result/Author.pm> and add the following method (as
1226 always, it must be above the closing "C<1;>"):
1229 # Row-level helper methods
1234 return $self->first_name . ' ' . $self->last_name;
1237 This will allow us to conveniently retrieve both the first and last name
1238 for an author in one shot. Now open C<root/src/books/list.tt2> and
1239 change the definition of C<tt_authors> from this:
1242 [% tt_authors = [ ];
1243 tt_authors.push(author.last_name) FOREACH author = book.authors %]
1249 [% tt_authors = [ ];
1250 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1253 (Only C<author.last_name> was changed to C<author.full_name> -- the rest
1254 of the file should remain the same.)
1256 Now go to the standard book list URL:
1258 http://localhost:3000/books/list
1260 The "Author(s)" column will now contain both the first and last name.
1261 And, because the concatenation logic was encapsulated inside our Result
1262 Class, it keeps the code inside our TT template nice and clean
1263 (remember, we want the templates to be as close to pure HTML markup as
1264 possible). Obviously, this capability becomes even more useful as you
1265 use it to remove even more complicated row-specific logic from your
1269 =head2 Moving Complicated View Code to the Model
1271 The previous section illustrated how we could use a Result Class method
1272 to print the full names of the authors without adding any extra code to
1273 our view, but it still left us with a fairly ugly mess (see
1274 C<root/src/books/list.tt2>):
1278 [% # NOTE: See Chapter 4 for a better way to do this! -%]
1279 [% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
1280 [% # loop in 'side effect notation' to load just the last names of the -%]
1281 [% # authors into the list. Note that the 'push' TT vmethod does not print -%]
1282 [% # a value, so nothing will be printed here. But, if you have something -%]
1283 [% # in TT that does return a method and you don't want it printed, you -%]
1284 [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to -%]
1285 [% # call it and discard the return value. -%]
1286 [% tt_authors = [ ];
1287 tt_authors.push(author.full_name) FOREACH author = book.authors %]
1288 [% # Now use a TT 'virtual method' to display the author count in parens -%]
1289 [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
1290 ([% tt_authors.size | html %])
1291 [% # Use another TT vmethod to join & print the names & comma separators -%]
1292 [% tt_authors.join(', ') | html %]
1296 Let's combine some of the techniques used earlier in this section to
1297 clean this up. First, let's add a method to our Book Result Class to
1298 return the number of authors for a book. Open
1299 C<lib/MyApp/Schema/Result/Book.pm> and add the following method:
1303 Return the number of authors for the current book
1310 # Use the 'many_to_many' relationship to fetch all of the authors for the current
1311 # and the 'count' method in DBIx::Class::ResultSet to get a SQL COUNT
1312 return $self->authors->count;
1315 Next, let's add a method to return a list of authors for a book to the
1316 same C<lib/MyApp/Schema/Result/Book.pm> file:
1320 Return a comma-separated list of authors for the current book
1327 # Loop through all authors for the current book, calling all the 'full_name'
1328 # Result Class method for each
1330 foreach my $author ($self->authors) {
1331 push(@names, $author->full_name);
1334 return join(', ', @names);
1337 This method loops through each author, using the C<full_name> Result
1338 Class method we added to C<lib/MyApp/Schema/Result/Author.pm> in the
1341 Using these two methods, we can simplify our TT code. Open
1342 C<root/src/books/list.tt2> and update the "Author(s)" table cell to
1343 match the following:
1347 [% # Print count and author list using Result Class methods -%]
1348 ([% book.author_count | html %]) [% book.author_list | html %]
1352 Although most of the code we removed comprised comments, the overall
1353 effect is dramatic... because our view code is so simple, we don't need
1354 huge comments to clue people in to the gist of our code. The view code
1355 is now self-documenting and readable enough that you could probably get
1356 by with no comments at all. All of the "complex" work is being done in
1357 our Result Class methods (and, because we have broken the code into
1358 nice, modular chunks, the Result Class code is hardly something you
1359 would call complex).
1361 As we saw in this section, always strive to keep your view AND
1362 controller code as simple as possible by pulling code out into your
1363 model objects. Because DBIx::Class can be easily extended in so many
1364 ways, it's an excellent to way accomplish this objective. It will make
1365 your code cleaner, easier to write, less error-prone, and easier to
1368 Before you conclude this section, hit Refresh in your browser... the
1369 output should be the same even though the backend code has been trimmed
1375 Kennedy Clark, C<hkclark@gmail.com>
1377 Feel free to contact the author for any errors or suggestions, but the
1378 best way to report issues is via the CPAN RT Bug system at
1379 <https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.
1381 The most recent version of the Catalyst Tutorial can be found at
1382 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.
1384 Copyright 2006-2010, Kennedy Clark, under the
1385 Creative Commons Attribution Share-Alike License Version 3.0
1386 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).