http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
-Your browser should display " Added book 'TCPIP_Illustrated_Vol-2' by
-'Stevens' with a rating of 5." along with a dump of the new book model
-object. You should also see the following DBIC debug messages displayed
-in the development server log messages if you have DBIC_TRACE set:
+Your browser should display "Added book 'TCPIP_Illustrated_Vol-2' by
+'Stevens' with a rating of 5." along with a dump of the new book model
+object as it was returned by DBIC. You should also see the following
+DBIC debug messages displayed in the development server log messages
+if you have DBIC_TRACE set:
INSERT INTO books (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
INSERT INTO book_authors (author_id, book_id) VALUES (?, ?): `4', `6'
there are now six books shown (if necessary, Shift+Reload or
Ctrl+Reload your browser at the C</books/list> page).
-Then I<add 2 more copies of the same book> so that we have some extras for
-our delete logic that will be coming up soon. Enter the same URL above
-two more times (or refresh your browser twice if it still contains this
-URL):
+
+=head1 CONVERT TO A CHAINED ACTION
+
+Although the example above uses the same C<Local> action type for the
+method that we saw in the previous part of the tutorial, there is an
+alternate approach that allows us to be more specific while also
+paving the way for more advanced capabilities. Change the method
+declaration for C<url_create> in C<lib/MyApp/Controller/Books.pm> you
+entered above to match the following:
+
+ sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
+
+This converts the method to take advantage of the Chained
+action/dispatch type. Chaining let's you have a single URL
+automatically dispatch to several controller methods, each of which
+can have precise control over the number of arguments that it will
+receive. A chain can essentially be thought of having three parts --
+a beginning, a middle and an end. The bullets below summarize the key
+points behind each of these parts of a chain:
+
+
+=over 4
+
+
+=item *
+
+Beginning
+
+=over 4
+
+=item *
+
+B<Use "C<:Chained('/')>" to start a chain>
+
+=item *
+
+Get arguments through C<CaptureArgs()>
+
+=item *
+
+Specify the path to match with C<PathPart()>
+
+=back
+
+
+=item *
+
+Middle
+
+=over 4
+
+=item *
+
+Link to previous part of the chain with C<:Chained('_name_')>
+
+=item *
+
+Get arguments through C<CaptureArgs()>
+
+=item *
+
+Specify the path to match with C<PathPart()>
+
+=back
+
+
+=item *
+
+End
+
+=over 4
+
+=item *
+
+Link to previous part of the chain with C<:Chained('_name_')>
+
+=item *
+
+B<Do NOT get arguments through "C<CaptureArgs()>," use "C<Args()>" instead to end a chain>
+
+=item *
+
+Specify the path to match with C<PathPart()>
+
+=back
+
+
+=back
+
+In our C<url_create> method above, we have combined all 3 parts into a
+single method: C<:Chained('/')> to start the chain,
+C<:PathPart('books/url_create')> to specify the base URL to match,
+along with C<:Args(3)> to capture exactly 3 arguments and also end the
+chain.
+
+As we will see shortly, a chain can consist of as many "links" as you
+wish, with each part capturing some arguments and doing some work
+along the way. We will continue to use the Chained action type in this
+part of the tutorial and explore slightly more advanced capabilities
+with the base method and delete feature below. But Chained dispatch
+is capable of far more. For additional information, see
+L<Catalyst::Manual::Intro/Action types>,
+L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained>,
+and the 2006 advent calendar entry on the subject:
+L<http://www.catalystframework.org/calendar/2006/10>.
+
+
+=head2 Try the Chained Action
+
+If you look back at the development server startup logs from your
+initial version of the C<url_create> method (the one using the
+C<:Local> attribute), you will notice that it produced output similar
+to the following:
+
+ [debug] Loaded Path actions:
+ .-------------------------------------+--------------------------------------.
+ | Path | Private |
+ +-------------------------------------+--------------------------------------+
+ | / | /default |
+ | / | /index |
+ | /books | /books/index |
+ | /books/list | /books/list |
+ | /books/url_create | /books/url_create |
+ '-------------------------------------+--------------------------------------'
+
+Now start the development server with our basic chained method in
+place and the startup debug output should change to something along
+the lines of the following:
+
+ [debug] Loaded Path actions:
+ .-------------------------------------+--------------------------------------.
+ | Path | Private |
+ +-------------------------------------+--------------------------------------+
+ | / | /default |
+ | / | /index |
+ | /books | /books/index |
+ | /books/list | /books/list |
+ '-------------------------------------+--------------------------------------'
+
+ [debug] Loaded Chained actions:
+ .-------------------------------------+--------------------------------------.
+ | Path Spec | Private |
+ +-------------------------------------+--------------------------------------+
+ | /books/url_create/*/*/* | /books/url_create |
+ '-------------------------------------+--------------------------------------'
+
+C<url_create> has disappeared form the "Loaded Path actions" section
+but it now shows up under the newly created "Loaded Chained actions"
+section. And, the "/*/*/*" portion clearly shows our requirement for
+three arguments.
+
+As with our non-chained version of C<url_create>, use your browser to
+enter the following URL:
+
+ http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
+
+You should see the same "Added book 'TCPIP_Illustrated_Vol-2' by
+'Stevens' with a rating of 5." along with a dump of the new book model
+object. Click the "Return to list" link, you should find that there
+are now seven books shown (two copies of TCPIP_Illustrated_Vol-2).
+
+
+=head2 Refactor to Use a "Base" Method to Start the Chains
+
+Let's make a quick update to our initial Chained action to show a
+little more of the power of chaining. First, open
+C<lib/MyApp/Controller/Books.pm> in your editor and add the following
+method:
+
+ =head2 base
+
+ Can place common logic to start chained dispatch here
+
+ =cut
+
+ sub base :Chained('/') :PathPart('books') :CaptureArgs(0) {
+ my ($self, $c) = @_;
+
+ # Store the resultset in stash so it's available for other methods
+ $c->stash->{resultset} = $c->model('DB::Books');
+
+ # Print a message to the debug log
+ $c->log->debug('*** INSIDE BASE METHOD ***');
+ }
+
+Here we print a log message and store the DBIC resultset in
+C<$c-E<gt>stash-E<gt>{resultset}> so that it's automatically available
+for other actions that chain off C<base>. If your controller always
+needs a book ID as it's first argument, you could have the base method
+capture that argument (with C<:CaptureArgs(1)>) and use it to pull the
+book object with C<-E<gt>find($id)> and leave it in the stash for
+later parts of your chains to then act upon. Because we have several
+actions that don't need to retrieve a book (such as the C<url_create>
+we are working with now), we will instead add that functionality
+to a common C<object> action shortly.
+
+As for C<url_create>, let's modify it to first dispatch to C<base>.
+Open up C<lib/MyApp/Controller/Books.pm> and edit the declaration for
+C<url_create> to match the following:
+
+ sub url_create :Chained('base') :PathPart('url_create') :Args(3) {
+
+Next, try out the refactored chain by restarting the development
+server. Notice that our "Loaded Chained actions" section has changed
+slightly:
+
+ [debug] Loaded Chained actions:
+ .-------------------------------------+--------------------------------------.
+ | Path Spec | Private |
+ +-------------------------------------+--------------------------------------+
+ | /books/url_create/*/*/* | /books/base (0) |
+ | | => /books/url_create |
+ '-------------------------------------+--------------------------------------'
+
+The "Path Spec" is the same, but now it maps to two Private actions as
+we would expect.
+
+Once again, enter the following URL into your browser:
http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4
-You should be able to click "Return to list" and now see 3 copies of
-"TCP_Illustrated_Vol-2".
+The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a
+rating of 5" message and dump of the new book object should appear.
+Also notice the extra debug message in the development server output
+from the C<base> method. Click the "Return to list" link, you should
+find that there are now eight books shown.
=head1 MANUALLY BUILDING A CREATE FORM
=cut
- sub form_create : Local {
+ sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
my ($self, $c) = @_;
# Set the TT template to use
=cut
- sub form_create_do : Local {
+ sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
my ($self, $c) = @_;
# Retrieve the values from the form
$ script/myapp_server.pl
+Notice that the server startup log reflects the two new chained
+methods that we added:
+
+ [debug] Loaded Chained actions:
+ .-------------------------------------+--------------------------------------.
+ | Path Spec | Private |
+ +-------------------------------------+--------------------------------------+
+ | /books/form_create | /books/base (0) |
+ | | => /books/form_create |
+ | /books/form_create_do | /books/base (0) |
+ | | => /books/form_create_do |
+ | /books/url_create/*/*/* | /books/base (0) |
+ | | => /books/url_create |
+ '-------------------------------------+--------------------------------------'
+
Point your browser to L<http://localhost:3000/books/form_create> and
enter "TCP/IP Illustrated, Vol 3" for the title, a rating of 5, and an
author ID of 4. You should then see the output of the same
</td>
<td>
[% # Add a link to delete a book %]
- <a href="[% c.uri_for('delete', book.id) %]">Delete</a>
+ <a href="[% c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
</td>
</tr>
[% END -%]
right side of the table with a C<Delete> "button" (for simplicity,
links will be used instead of full HTML buttons).
-B<Note:> You should use more than just a simple link with your
-applications. Consider using some sort of of confirmation page
+Also notice that we are using a more advanced form of C<uri_for> than
+we have seen before. Here we use C<$c-E<gt>controller-
+E<gt>action_for> to automatically generate a URI appropriate for that
+action based on the method we want to link to while inserting the
+C<book.id> value into the appropriate place. Now, if you ever change
+C<:PathPart('delete')> in your controller method to
+C<:PathPart('kill')>, then your links will automatically update
+without any changes to your .tt2 template file. As long as the name
+of your method does not changed ("delete" here), then your links will
+still be correct. There are a few shortcuts and options when using
+C<action_for()>:
+
+=over 4
+
+=item *
+
+If you are referring to a method in the current controller, you can
+use C<$self-E<gt>action_for('_method_name_')>.
+
+=item *
+
+If you are referring to a method in a different controller, you need
+to include that controller's name as an argument to C<controller()>, as in
+C<$c-E<gt>controller('_controller_name_')-E<gt>action_for('_method_name_')>.
+
+=back
+
+B<Note:> In general, you should use more than just a simple link with
+your applications. Consider using some sort of of confirmation page
(typically with unique actions in your controller for both the
confirmation and the actual delete operation). Also, you should try
to use an HTTP POST operation (versus the GET used here) for
database).
+=head2 Add a Common Method to Retrieve a Book for the Chain
+
+As mentioned earlier, since we have a mixture of actions that operate
+on a single book ID and others that do no, we should not have C<base>
+capture the book ID, find the corresponding book in the database and
+save it in the stash for later links in the chain. However, just
+because that logic does not belong in C<base> doesn't mean that we
+can't create another location to centralize the book lookup code. In
+our case, we will create a method called C<object> that will store the
+specific book in the stash. Chains that always operate on a single
+existing book can chain off this method, but methods such as
+C<url_create> that don't operate on an existing book can chain
+directly off base.
+
+To add the C<object> method, edit C<lib/MyApp/Controller/Books.pm>
+and add the following code:
+
+ =head2 object
+
+ Fetch the specified book object based on the book ID and store
+ it in the stash
+
+ =cut
+
+ sub object :Chained('base') :PathPart('id') :CaptureArgs(1) {
+ # $id = primary key of book to delete
+ my ($self, $c, $id) = @_;
+
+ # Find the book object and store it in the stash
+ $c->stash(object => $c->stash->{resultset}->find($id));
+
+ # Make sure the lookup was successful. You would probably
+ # want to do something like this in a real app:
+ # $c->detach('/error_404') if !$c->stash->{object};
+ die "Book $id not found!" if !$c->stash->{object};
+ }
+
+Now, any other method that chains off C<object> will automatically
+have the appropriate book waiting for it in
+C<$c-E<gt>stash-Egt>{object}>.
+
+Also note that we are using different technique for setting
+C<$c-E<gt>stash>. The advantage of this style is that it let's you
+set multiple stash variables at a time. For example:
+
+ $c->stash(object => $c->stash->{resultset}->find($id),
+ another_thing => 1);
+
+or as a hashref:
+
+ $c->stash({object => $c->stash->{resultset}->find($id),
+ another_thing => 1});
+
+Either format works, but the C<$c-E<gt>stash(name =E<gt> value);>
+style is growing in popularity -- you may which to use it all
+the time (even when you are only setting a single value).
+
+
=head2 Add a Delete Action to the Controller
Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
=cut
- sub delete : Local {
- # $id = primary key of book to delete
- my ($self, $c, $id) = @_;
+ sub delete :Chained('object') :PathPart('delete') :Args(0) {
+ my ($self, $c) = @_;
- # Search for the book and then delete it
- $c->model('DB::Books')->search({id => $id})->delete_all;
+ # Use the book object saved by 'object' and delete it along
+ # with related 'book_authors' entries
+ $c->stash->{object}->delete;
# Set a status message to be displayed at the top of the view
$c->stash->{status_msg} = "Book deleted.";
$c->forward('list');
}
-This method first deletes the book with the specified primary key ID.
-However, it also removes the corresponding entry from the
-C<book_authors> table. Note that C<delete_all> was used instead of
-C<delete>: whereas C<delete_all> also removes the join table entries in
-C<book_authors>, C<delete> does not (only use C<delete_all> if you
-really need the cascading deletes... otherwise you are wasting resources).
+This method first deletes the book object saved by the C<object> method.
+However, it also removes the corresponding entry from the
+C<book_authors> table with a cascading delete.
Then, rather than forwarding to a "delete done" page as we did with the
earlier create example, it simply sets the C<status_msg> to display a
If the application is still running from before, use C<Ctrl-C> to kill
it. Then restart the server:
- $ script/myapp_server.pl
+ $ DBIC_TRACE=1 script/myapp_server.pl
+
+The C<delete> method now appears in the "Loaded Chained actions" section
+of the startup debug output:
+
+ [debug] Loaded Chained actions:
+ .-------------------------------------+--------------------------------------.
+ | Path Spec | Private |
+ +-------------------------------------+--------------------------------------+
+ | /books/id/*/delete | /books/base (0) |
+ | | -> /books/object (1) |
+ | | => /books/delete |
+ | /books/form_create | /books/base (0) |
+ | | => /books/form_create |
+ | /books/form_create_do | /books/base (0) |
+ | | => /books/form_create_do |
+ | /books/url_create/*/*/* | /books/base (0) |
+ | | => /books/url_create |
+ '-------------------------------------+--------------------------------------'
Then point your browser to L<http://localhost:3000/books/list> and click
the "Delete" link next to the first "TCPIP_Illustrated_Vol-2". A green
"Book deleted" status message should display at the top of the page,
-along with a list of the eight remaining books.
+along with a list of the eight remaining books. You will also see the
+cascading delete operation via the DBIC_TRACE output:
+
+ DELETE FROM books WHERE ( id = ? ): '6'
+ SELECT me.book_id, me.author_id FROM book_authors me WHERE ( me.book_id = ? ): '6'
+ DELETE FROM book_authors WHERE ( author_id = ? AND book_id = ? ): '4', '6'
=head2 Fixing a Dangerous URL
http://localhost:3000/books/delete/6
-What if the user were to press reload with this URL still active? In
-this case the redundant delete is harmless, but in other cases this
-could clearly be extremely dangerous.
+What if the user were to press reload with this URL still active? In
+this case the redundant delete is harmless (although it does generate
+an exception screen, it doesn't perform any undesirable actions on the
+application or database), but in other cases this could clearly be
+extremely dangerous.
We can improve the logic by converting to a redirect. Unlike
C<$c-E<gt>forward('list'))> or C<$c-E<gt>detach('list'))> that perform
open C<lib/MyApp/Controller/Books.pm> and edit the existing
C<sub delete> method to match:
- =head2 delete
+ =head2 delete
Delete a book
-
+
=cut
- sub delete : Local {
- # $id = primary key of book to delete
- my ($self, $c, $id) = @_;
+ sub delete :Chained('object') :PathPart('delete') :Args(0) {
+ my ($self, $c) = @_;
- # Search for the book and then delete it
- $c->model('DB::Books')->search({id => $id})->delete_all;
+ # Use the book object saved by 'object' and delete it along
+ # with related 'book_authors' entries
+ $c->stash->{object}->delete;
# Set a status message to be displayed at the top of the view
$c->stash->{status_msg} = "Book deleted.";
- # Redirect the user back to the list page
- $c->response->redirect($c->uri_for('/books/list'));
+ # Redirect the user back to the list page. Note the use
+ # of $self->action_for as earlier in this section (BasicCRUD)
+ $c->response->redirect($c->uri_for($self->action_for('list')));
}
=head2 Try the Delete and Redirect Logic
Restart the development server and point your browser to
-L<http://localhost:3000/books/list> and delete the first copy of
-"TCPIP_Illustrated_Vol-2". The URL in your browser should return to
-the L<http://localhost:3000/books/list> URL, so that is an
-improvement, but notice that I<no green "Book deleted" status message
-is displayed>. Because the stash is reset on every request (and a
-redirect involves a second request), the C<status_msg> is cleared
-before it can be displayed.
+L<http://localhost:3000/books/list> (don't just hit "Refresh" in your
+browser since we left the URL in an invalid state in the previous
+section!) and delete the first copy of the remaining two
+"TCPIP_Illustrated_Vol-2" books. The URL in your browser should return
+to the L<http://localhost:3000/books/list> URL, so that is an
+improvement, but notice that I<no green "Book deleted" status message is
+displayed>. Because the stash is reset on every request (and a redirect
+involves a second request), the C<status_msg> is cleared before it can
+be displayed.
=head2 Using C<uri_for> to Pass Query Parameters
-There are several ways to pass information across a redirect.
-In general, the best option is to use the C<flash> technique that we
-will see in Part 5 of the tutorial; however, here we will pass the
-information via query parameters on the redirect itself. Open
-C<lib/MyApp/Controller/Books.pm> and update the existing
-C<sub delete> method to match the following:
+There are several ways to pass information across a redirect. One
+option is to use the C<flash> technique that we will see in Part 5 of
+the tutorial; however, here we will pass the information via query
+parameters on the redirect itself. Open
+C<lib/MyApp/Controller/Books.pm> and update the existing C<sub delete>
+method to match the following:
=head2 delete
=cut
- sub delete : Local {
- # $id = primary key of book to delete
- my ($self, $c, $id) = @_;
+ sub delete :Chained('object') :PathPart('delete') :Args(0) {
+ my ($self, $c) = @_;
- # Search for the book and then delete it
- $c->model('DB::Books')->search({id => $id})->delete_all;
+ # Use the book object saved by 'object' and delete it along
+ # with related 'book_authors' entries
+ $c->stash->{object}->delete;
# Redirect the user back to the list page with status msg as an arg
- $c->response->redirect($c->uri_for('/books/list',
+ $c->response->redirect($c->uri_for($self->action_for('list'),
{status_msg => "Book deleted."}));
}
This modification simply leverages the ability of C<uri_for> to include
an arbitrary number of name/value pairs in a hash reference. Next, we
-need to update C<root/src/wrapper> to handle C<status_msg> as a
+need to update C<root/src/wrapper.tt2> to handle C<status_msg> as a
query parameter:
...
=head2 Try the Delete and Redirect With Query Param Logic
Restart the development server and point your browser to
-L<http://localhost:3000/books/list>. Then delete the remaining copy
-of "TCPIP_Illustrated_Vol-2". The green "Book deleted" status message
+L<http://localhost:3000/books/list> (you should now be able to safely
+hit "refresh" in your browser). Then delete the remaining copy of
+"TCPIP_Illustrated_Vol-2". The green "Book deleted" status message
should return.
-B<NOTE:> Although this did present an opportunity to show a handy
-capability of C<uri_for>, it would be much better to use Catalyst's
-C<flash> feature in this situation. Although the technique here is
-less dangerous than leaving the delete URL in the client's browser,
-we have still exposed the status message to the user. With C<flash>,
-this message returns to its rightful place as a service-side
-mechanism (we will migrate this code to C<flash> in the next part
-of the tutorial).
+B<NOTE:> Another popular method for maintaining server-side
+information across a redirect is to use the C<flash> technique we
+discuss in the next part of the tutorial,
+L<Authentication|Catalyst::Manual::Tutorial::Authentication>. While
+C<flash> is a "slicker" mechanism in that it's all handled by the
+server and doesn't "pollute" your URLs, B<it is important to note that
+C<flash> can lead to situations where the wrong information shows up
+in the wrong browser window if the user has multiple windows or
+browser tabs open.> For example, Window A causes something to be
+placed in the stash, but before that window performs a redirect,
+Window B makes a request to the server and gets the status information
+that should really go to Window A. For this reason, you may wish
+to use the "query param" technique shown here in your applications.
=head1 AUTHOR
Copyright 2006-2008, Kennedy Clark, under Creative Commons License
(L<http://creativecommons.org/licenses/by-sa/3.0/us/>).
-
projects / catagits/Catalyst-Manual.git / blobdiff