Catalys...sicCRUD(3)

💖 Catalyst::Manual::Tutorial::04_BasicCRUD — Catalyst Tutorial, Chapter 4: Basic CRUD 💖

Okay bestie, so this is literally Chapter 4 of 10 in the Catalyst tutorial and it's giving "we're actually building stuff now" energy. Let me break it down for you 💅

---

✨ OVERVIEW ✨

So this is Chapter 4 of 10 for the Catalyst tutorial, periodt.

Tutorial Overview (the whole saga, iykyk):

1. Introduction
2. Catalyst Basics
3. More Catalyst Basics
4. 04_Basic CRUD ← you are here 🎯
5. Authentication
6. Authorization
7. Debugging
8. Testing
9. Advanced CRUD
10. Appendices

---

🌸 DESCRIPTION 🌸

Okay so this chapter builds on the fairly primitive application from Chapter 3 (no shade, it was cute) and adds basic support for Create, Read, Update, and Delete (CRUD) of Book objects. Obsessed.

So here's the tea: the 'list' function in Chapter 3 already implements the Read portion of CRUD — well, technically Read normally refers to reading a single object, but you could implement full Read functionality using the techniques introduced below. Either way 💁‍♀️

This section is gonna focus on the Create and Delete aspects of CRUD. More advanced capabilities — including full Update functionality — will be addressed in Chapter 9. Fr fr, we're keeping it basic here.

So even though this chapter will show you how to build CRUD functionality yourself (DIY queen energy 👑), another option is to use a "CRUD builder" type of tool to automate the process. You get less control, but it can be quick and easy. For example, see Catalyst::Plugin::AutoCRUD, CatalystX::CRUD, and CatalystX::CRUD::YUI. Slay, options ✨

Source code for the tutorial is included in the /home/catalyst/Final directory of the Tutorial Virtual machine (one subdirectory per chapter, bestie 🫶). There are also instructions for downloading the code in Catalyst::Manual::Tutorial::01_Intro.

---

🦋 FORMLESS SUBMISSION 🦋

Our initial attempt at object creation is gonna utilize the "URL arguments" feature of Catalyst — we will employ the more common form-based submission in the sections that follow. Lowkey starting simple, highkey iconic 💅

🌈 Include a Create Action in the Books Controller 🌈

Edit lib/MyApp/Controller/Books.pm and enter the following method:

    =head2 url_create

    Create a book with the supplied title, rating, and author

    =cut

    sub url_create :Local {
        # In addition to self & context, get the title, rating, &
        # author_id args from the URL.  Note that Catalyst automatically
        # puts extra information after the "/<controller_name>/<action_name/"
        # into @_.  The args are separated  by the '/' char on the URL.
        my ($self, $c, $title, $rating, $author_id) = @_;

        # Call create() on the book model object. Pass the table
        # columns/field values we want to set as hash values
        my $book = $c->model('DB::Book')->create({
                title  => $title,
                rating => $rating
            });

        # Add a record to the join table for this book, mapping to
        # appropriate author
        $book->add_to_book_authors({author_id => $author_id});
        # Note: Above is a shortcut for this:
        # $book->create_related('book_authors', {author_id => $author_id});

        # Assign the Book object to the stash for display and set template
        $c->stash(book     => $book,
                  template => 'books/create_done.tt2');

        # Disable caching for this page
        $c->response->header('Cache-Control' => 'no-cache');
    }

Notice that Catalyst takes "extra slash-separated information" from the URL and passes it as arguments in @_ — as long as the number of arguments is not "fixed" using an attribute like :Args(0) 👀. The "url_create" action then uses a simple call to the DBIC "create" method to add the requested information to the database (with a separate call to "add_to_book_authors" to update the join table). As do virtually all controller methods (at least the ones that directly handle user input), it then sets the template that should handle this request. Werk 💅

Also note that we are explicitly setting a "no-cache" "Cache-Control" header to force browsers using the page to get a fresh copy every time. You could even move this to a "auto" method in lib/MyApp/Controller/Root.pm and it would automatically get applied to every page in the whole application via a single line of code — remember from Chapter 3, that every "auto" method gets run in the Controller hierarchy ✨

🎀 Include a Template for the 'url_create' Action: 🎀

Edit root/src/books/create_done.tt2 and then enter:

    [% # Use the TT Dumper plugin to Data::Dumper variables to the browser   -%]
    [% # Not a good idea for production use, though. :-)  'Indent=1' is      -%]
    [% # optional, but prevents "massive indenting" of deeply nested objects -%]
    [% USE Dumper(Indent=1) -%]

    [% # Set the page title.  META can 'go back' and set values in templates -%]
    [% # that have been processed 'before' this template (here it's updating -%]
    [% # the title in the root/src/wrapper.tt2 wrapper template).  Note that -%]
    [% # META only works on simple/static strings (i.e. there is no variable   -%]
    [% # interpolation -- if you need dynamic/interpolated content in your   -%]
    [% # title, set "$c->stash(title => $something)" in the controller).     -%]
    [% META title = 'Book Created' %]

    [% # Output information about the record that was added.  First title.   -%]
    <p>Added book '[% book.title %]'

    [% # Then, output the last name of the first author -%]
    by '[% book.authors.first.last_name %]'

    [% # Then, output the rating for the book that was added -%]
    with a rating of [% book.rating %].</p>

    [% # Provide a link back to the list page.  'c.uri_for' builds -%]
    [% # a full URI; e.g., 'http://localhost:3000/books/list'      -%]
    <p><a href="[% c.uri_for('/books/list') %]">Return to list</a></p>

    [% # Try out the TT Dumper (for development only!) -%]
    <pre>
    Dump of the 'book' variable:
    [% Dumper.dump(book) %]
    </pre>

The TT "USE" directive allows access to a variety of plugin modules (TT plugins, that is, not Catalyst plugins — don't get it twisted 😭) to add extra functionality to the base TT capabilities. Here, the plugin allows Data::Dumper "pretty printing" of objects and variables. Other than that, the rest of the code should be familiar from the examples in Chapter 3. Iconic.

🔥 Try the 'url_create' Feature 🔥

Make sure the development server is running with the "-r" restart option:

$ DBIC_TRACE=1 script/myapp_server.pl -r

Note that new path for /books/url_create appears in the startup debug output.

Next, use your browser to enter the following URL:

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 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 book (rating, title) VALUES (?, ?): `5', `TCPIP_Illustrated_Vol-2'
INSERT INTO book_author (author_id, book_id) VALUES (?, ?): `4', `6'

The "INSERT" statements are obviously adding the book and linking it to the existing record for Richard Stevens. The "SELECT" statement results from DBIC automatically fetching the book for the "Dumper.dump(book)". No cap, that's literally what's happening 💀

If you then click the "Return to list" link, you should find that there are now six books shown (if necessary, Shift+Reload or Ctrl+Reload your browser at the /books/list page — bestie, the cache WILL gaslight you 🌸). You should now see the six DBIC debug messages similar to the following (where N = 1–6):

SELECT author.id, author.first_name, author.last_name
    FROM book_author me  JOIN author author
    ON author.id = me.author_id WHERE ( me.book_id = ? ): 'N'

---

to be continued, bestie — more parts incoming 💖✨

✨ CONVERT TO A CHAINED ACTION ✨

Okay bestie, so the example above uses the same "Local" action type for the method that we saw in the previous chapter of the tutorial — but there’s an alternate approach that lets us be more specific and paves the way for more advanced capabilities. Change the method declaration for url_create in lib/MyApp/Controller/Books.pm that you entered above to match this:

           sub url_create :Chained('/') :PathPart('books/url_create') :Args(3) {
               # In addition to self & context, get the title, rating, &
               # author_id args from the URL.  Note that Catalyst automatically
               # puts the first 3 arguments worth of extra information after the
               # "/<controller_name>/<action_name/" into @_ because we specified
               # "Args(3)".  The args are separated  by the '/' char on the URL.
               my ($self, $c, $title, $rating, $author_id) = @_;

               ...

This converts the method to take advantage of the Chained action/dispatch type. Chaining lets you have a single URL automatically dispatch to several controller methods, and each one can have precise control over how many arguments it receives. A chain can basically be thought of as having three parts — a beginning, a middle, and an end. The bullets below summarize the key points behind each of those parts:

• Beginning
  • Use :Chained('/') to start a chain
  • Get arguments through CaptureArgs()
  • Specify the path to match with PathPart()
• Middle
  • Link to the previous part of the chain with :Chained('_name_')
  • Get arguments through CaptureArgs()
  • Specify the path to match with PathPart()
• End
  • Link to the previous part of the chain with :Chained('_name_')
  • Do NOT get arguments through "CaptureArgs()," — use "Args()" instead to end a chain
  • Specify the path to match with PathPart()

In our url_create method above, we have combined all three parts into a single method: :Chained('/') to start the chain, :PathPart('books/url_create') to specify the base URL to match, and :Args(3) to capture exactly three arguments and to 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 chapter 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 "Action types" in Catalyst::Manual::Intro, Catalyst::DispatchType::Chained, and the 2006 Advent calendar entry on the subject: http://www.catalystframework.org/calendar/2006/10.

🦋 Try the Chained Action 🦋

If you look back at the development server startup logs from your initial version of the url_create method (the one using the :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                    |
           '-------------------------------------+--------------------------------------'

When the development server restarts after our conversion to Chained dispatch, the 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                    |
           '-------------------------------------+--------------------------------------'

url_create has disappeared from 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 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, and you should find that there are now seven books shown (two copies of TCPIP_Illustrated_Vol-2).

🎀 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 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::Book'));

               # 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 $c->stash->{resultset} so that it’s automatically available for other actions that chain off base. If your controller always needs a book ID as its first argument, you could have the base method capture that argument (with :CaptureArgs(1)) and use it to pull the book object with ->find($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 url_create we are working with now), we will instead add that functionality to a common object action shortly.

As for url_create, let’s modify it to first dispatch to base. Open up lib/MyApp/Controller/Books.pm and edit the declaration for url_create to match the following:

           sub url_create :Chained('base') :PathPart('url_create') :Args(3) {

Once you save lib/MyApp/Controller/Books.pm, notice that the development server will restart and our Loaded Chained actions section will change a little:

           [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. The base method is being triggered by the /books part of the URL. However, the processing then continues to the url_create method because this method “chained” off base and specified :PathPart('url_create') (note that we could have omitted the PathPart here because it matches the name of the method, but we will include it to make the logic as explicit as possible).

Once again, enter the following URL into your browser:

http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4

The same "Added book 'TCPIP_Illustrated_Vol-2' by 'Stevens' with a rating of 5." message and a dump of the new book object should appear. Also notice the extra "INSIDE BASE METHOD" debug message in the development server output from the base method. Click the "Return to list" link, and you should find that there are now eight books shown. (You may have a larger number of books if you repeated any of the "create" actions more than once. Don’t worry about it as long as the number of books is appropriate for the number of times you added new books… there should be the original five books added via myapp01.sql plus one additional book for each time you ran one of the url_create variations above.)

🎀 MANUALLY BUILDING A CREATE FORM 🎀

Okay so like — the url_create action from the last bit? It absolutely ate at showing off how powerful and flexible Catalyst and DBIC are, no cap. But bestie... it is not a realistic way to expect actual humans to enter data 💀. Not even close. This whole section starts dealing with that (though honestly only barely — Chapter 9 has the good stuff for handling web-based forms, iykyk).

✨ Add Method to Display The Form ✨

Open up lib/MyApp/Controller/Books.pm and drop this method in:

=head2 form_create

Display form to collect information for book to create

=cut

sub form_create :Chained('base') :PathPart('form_create') :Args(0) {
    my ($self, $c) = @_;

    # Set the TT template to use
    $c->stash(template => 'books/form_create.tt2');
}

That's it. It literally just invokes a view containing a form to create a book. Simple. Iconic. Minimal effort, maximum vibe 🫶.

🌸 Add a Template for the Form 🌸

Pop open root/src/books/form_create.tt2 in your editor and type this in:

[% META title = 'Manual Form Book Create' -%]

<form method="post" action="[% c.uri_for('form_create_do') %]">
<table>
    <tr><td>Title:</td><td><input type="text" name="title"></td></tr>
    <tr><td>Rating:</td><td><input type="text" name="rating"></td></tr>
    <tr><td>Author ID:</td><td><input type="text" name="author_id"></td></tr>
</table>
<input type="submit" name="Submit" value="Submit">
</form>

Notice how the form's target is set to "form_create_do" — that's the method we're making in the very next section, so like, don't panic that it doesn't exist yet 💅.

💖 Add a Method to Process Form Values and Update Database 💖

Back into lib/MyApp/Controller/Books.pm, add this method to save the form info into the database:

=head2 form_create_do

Take information from form and add to database

=cut

sub form_create_do :Chained('base') :PathPart('form_create_do') :Args(0) {
    my ($self, $c) = @_;

    # Retrieve the values from the form
    my $title     = $c->request->params->{title}     || 'N/A';
    my $rating    = $c->request->params->{rating}    || 'N/A';
    my $author_id = $c->request->params->{author_id} || '1';

    # Create the book
    my $book = $c->model('DB::Book')->create({
            title   => $title,
            rating  => $rating,
        });
    # Handle relationship with author
    $book->add_to_book_authors({author_id => $author_id});
    # Note: Above is a shortcut for this:
    # $book->create_related('book_authors', {author_id => $author_id});

    # Store new model object in stash and set template
    $c->stash(book     => $book,
              template => 'books/create_done.tt2');
}

🦋 Test Out The Form 🦋

Bestie, look at the server startup log — it's literally reflecting the two new chained methods we just 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                 |
'-------------------------------------+--------------------------------------'

Now point your browser at <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 create_done.tt2 template from the earlier examples 💜. Finally, click "Return to list" to see the full list of books. Slay 🎉.

Note: making the user type in the primary key ID for the author is obviously crude 🙈. We're gonna fix that whole situation with a drop-down list and add validation to our forms in Chapter 9 ✨.

---

💀 A SIMPLE DELETE FEATURE 💀

Turning our attention to the Delete part of CRUD — this section walks through some basic techniques for removing info from the database. Bye-bye data, hello main character energy 🔥.

🍓 Include a Delete Link in the List 🍓

Edit root/src/books/list.tt2 and update it so it matches this — two sections changed: 1) the extra <th>Links</th> table header, and 2) the five lines for the Delete link down near the bottom:

[% # This is a TT comment. -%]

[%- # Provide a title -%]
[% META title = 'Book List' -%]

[% # Note That the '-' at the beginning or end of TT code  -%]
[% # "chomps" the whitespace/newline at that end of the    -%]
[% # output (use View Source in browser to see the effect) -%]

[% # Some basic HTML with a loop to display books -%]
<table>
<tr><th>Title</th><th>Rating</th><th>Author(s)</th><th>Links</th></tr>
[% # Display each book in a table row %]
[% FOREACH book IN books -%]
    <tr>
        <td>[% book.title %]</td>
        <td>[% book.rating %]</td>
        <td>
            [% # NOTE: See Chapter 4 for a better way to do this!                      -%]
            [% # First initialize a TT variable to hold a list.  Then use a TT FOREACH -%]
            [% # loop in 'side effect notation' to load just the last names of the     -%]
            [% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
            [% # a value, so nothing will be printed here.  But, if you have something -%]
            [% # in TT that does return a value and you don't want it printed, you     -%]
            [% # 1) assign it to a bogus value, or                                     -%]
            [% # 2) use the CALL keyword to call it and discard the return value.      -%]
            [% tt_authors = [ ];
              tt_authors.push(author.last_name) FOREACH author = book.authors %]
            [% # Now use a TT 'virtual method' to display the author count in parens   -%]
            [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
            ([% tt_authors.size | html %])
            [% # Use another TT vmethod to join & print the names & comma separators   -%]
            [% tt_authors.join(', ') | html %]
        </td>
        <td>
            [% # Add a link to delete a book %]
            <a href="[%
                c.uri_for(c.controller.action_for('delete'), [book.id]) %]">Delete</a>
        </td>
    </tr>
[% END -%]
</table>

The extra code is obviously there to add a brand new column on the right side of the table with a "Delete" "button" 🎀 (for simplicity we're using links instead of full HTML buttons; but in practice, anything that modifies data should be handled with a form sending a POST request — remember that!).

Also, notice we're using a fancier form of uri_for than we've seen before ✨. Here we use $c->controller->action_for to automatically generate a URI appropriate for that action based on the method we want to link to, while slotting the book.id value into the right place. So now if you ever change :PathPart('delete') in your controller method to something like :PathPart('kill'), your links update automatically with zero changes to your .tt2 template file. As long as your method's name doesn't change (here, "delete"), your links stay correct 👑. There are a few shortcuts and options when using action_for():

• If you're referring to a method in the current controller, you can use $self->action_for('_method_name_') (where _method_name_ is, like, the method name obviously).
• If you're referring to a method in a different controller, you need to include that controller's name as an argument to controller(), like this: $c->controller('_controller_name_')->action_for('_method_name_') (with _controller_name_ and _method_name_ as your placeholders).

Note: in practice you should never use a GET request to delete a record — always use POST for actions that will modify data 💀. We're only doing it here for illustrative and simplicity purposes. Do not copy this energy into production, bestie, I'm begging.

🌈 Add a Common Method to Retrieve a Book for the Chain 🌈

Like we mentioned earlier: since we've got a mix of actions that operate on a single book ID and others that don't, we should not have base capture the book ID, find the matching book in the database, and stash it for later links in the chain. But — and hear me out — just because that logic doesn't belong in base doesn't mean we can't make another spot to centralize the book lookup code 🫶. In our case we'll make a method called object that stores the specific book in the stash. Chains that always operate on a single existing book can chain off this method, while methods like url_create that don't operate on an existing book can chain directly off base.

To add the object method, edit lib/MyApp/Controller/Books.pm and add this 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};

    # Print a message to the debug log
    $c->log->debug("*** INSIDE OBJECT METHOD for obj id=$id ***");
}

Now literally any other method that chains off object will automatically have the right book just chilling there waiting for it in $c->stash->{object} 💅.

⭐ Add a Delete Action to the Controller ⭐

Open lib/MyApp/Controller/Books.pm in your editor and add this method:

=head2 delete

Delete a book

=cut

sub delete :Chained('object') :PathPart('delete') :Args(0) {
    my ($self, $c) = @_;

    # Use the book object saved by 'object' and delete it along
    # with related 'book_author' entries
    $c->stash->{object}->delete;

    # Set a status message to be displayed at the top of the view
    $c->stash->{status_msg} = "Book deleted.";

    # Forward to the list action/method in this controller
    $c->forward('list');
}

Like, this method does two things at once — first it deletes the book object that our object method already stashed for us, and also removes the matching row from the book_author table via a cascading delete. Two-for-one slay 🎀

Then — plot twist — instead of forwarding to a "delete done" page like we did in the earlier create example, it just sets status_msg so a little notification shows up for the user while the normal list view renders. Iconic, low-effort, works. 💅

The delete action uses the context forward method to bounce the user back to the book list. We could have used detach too, bestie — the difference is: forward returns to the original action once it's done, while detach does not return at all. Other than that one thing, the two are literally equivalent. ✨

Try the Delete Feature 🌸

Once you save the Books controller, the server should auto-restart itself (yes queen, it just knows). The delete method should now show up 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 at <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. 👑

You'll also see the cascading delete operation happening in the DBIC_TRACE output:

SELECT me.id, me.title, me.rating FROM book me WHERE ( ( me.id = ? ) ): '6'
DELETE FROM book WHERE ( id = ? ): '6'

If you get the error file error - books/delete.tt2: not found then you probably forgot to uncomment the template line in sub list at the end of chapter 3. Been there, girl. 😭

Fixing a Dangerous URL 🚨

Look at the URL in your browser once you've done the deletion in the prior step — it's still referencing the delete action:

http://localhost:3000/books/id/6/delete

So like… what if the user hits reload with this URL still active? In this case the redundant delete is harmless (it does generate an exception screen, but it doesn't perform any undesirable actions on the application or database) — but in other cases this could clearly lead to trouble. Not the vibe. 💀

We can improve the logic by converting to a redirect. Unlike $c->forward('list')) or $c->detach('list')) — which perform a server-side alteration in the flow of processing — a redirect is a client-side mechanism that makes the browser issue an entirely new request. As a result, the URL in the browser gets updated to match the destination of the redirection URL. ✨

To convert the forward used in the previous section to a redirect, open lib/MyApp/Controller/Books.pm and edit the existing sub delete method to match:

=head2 delete

Delete a book

=cut

sub delete :Chained('object') :PathPart('delete') :Args(0) {
    my ($self, $c) = @_;

    # Use the book object saved by 'object' and delete it along
    # with related 'book_author' 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.  Note the use
    # of $self->action_for as earlier in this section (BasicCRUD)
    $c->response->redirect($c->uri_for($self->action_for('list')));
}

Try the Delete and Redirect Logic 🦋

Point your browser to <http://localhost:3000/books/list> (and do not 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 <http://localhost:3000/books/list> URL, so that's an improvement — but notice that no green "Book deleted" status message is displayed. 😭 Why? Because the stash is reset on every request (and a redirect involves a second request), so the status_msg gets cleared before it can ever be displayed. Rude, honestly.

Using 'uri_for' to Pass Query Parameters 💜

There are several ways to pass information across a redirect. One option is the flash technique that we'll see in Chapter 5 of this tutorial; however, here we'll pass the information via query parameters on the redirect itself. Open lib/MyApp/Controller/Books.pm and update the existing sub delete method to match the following:

=head2 delete

Delete a book

=cut

sub delete :Chained('object') :PathPart('delete') :Args(0) {
    my ($self, $c) = @_;

    # Use the book object saved by 'object' and delete it along
    # with related 'book_author' 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($self->action_for('list'),
        {status_msg => "Book deleted."}));
}

This modification simply leverages the ability of uri_for to include an arbitrary number of name/value pairs in a hash reference. Obsessed with her. 💖

Next, we need to update root/src/wrapper.tt2 to handle status_msg as a query parameter:

...
<div id="content">
    [%# Status and error messages %]
    <span class="message">[%
        status_msg || c.request.params.status_msg | html %]</span>
    <span class="error">[% error_msg %]</span>
    [%# This is where TT will stick all of your template's contents. -%]
    [% content %]
</div><!-- end content -->
...

Even though the sample above only shows the content div, leave the rest of the file intact — the only change we made to the wrapper.tt2 was adding "|| c.request.params.status_msg" to the <span class="message"> line. 🌈

Note that we definitely want the "| html" TT filter here, bestie. It would be super easy for users to modify the message on the URL and possibly inject harmful code into the application if we left that off. No cap, keep the filter. 🔥

Try the Delete and Redirect With Query Param Logic 🧚

Point your browser to <http://localhost:3000/books/list> (you should now be able to safely hit "refresh" in your browser, queen). Then delete the remaining copy of "TCPIP_Illustrated_Vol-2". The green "Book deleted" status message should return. 🎀

But notice that you can now hit the "Reload" button in your browser and it just redisplays the book list (and it correctly shows it without the "Book deleted" message on redisplay). Literally flawless behaviour. ✨

NOTE: Be sure to check out Authentication where we use an improved technique that is better suited to your real world applications. 👑

---

🔥 EXPLORING THE POWER OF DBIC 🔥

In this section we're gonna explore some additional capabilities offered by DBIx::Class. Although these features have relatively little to do with Catalyst per se, you will almost certainly want to take advantage of them in your applications. Trust. 💅

Add Datetime Columns to Our Existing Books Table ⭐

Let's add two columns to our existing books table so we can track when each book was added and when each book is updated:

$ sqlite3 myapp.db
sqlite> ALTER TABLE book ADD created TIMESTAMP;
sqlite> ALTER TABLE book ADD updated TIMESTAMP;
sqlite> UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
sqlite> SELECT * FROM book;
1|CCSP SNRS Exam Certification Guide|5|2010-02-16 04:15:45|2010-02-16 04:15:45
2|TCP/IP Illustrated, Volume 1|5|2010-02-16 04:15:45|2010-02-16 04:15:45
3|Internetworking with TCP/IP Vol.1|4|2010-02-16 04:15:45|2010-02-16 04:15:45
4|Perl Cookbook|5|2010-02-16 04:15:45|2010-02-16 04:15:45
5|Designing with Web Standards|5|2010-02-16 04:15:45|2010-02-16 04:15:45
9|TCP/IP Illustrated, Vol 3|5|2010-02-16 04:15:45|2010-02-16 04:15:45
sqlite> .quit
$

Here are the commands without the surrounding sqlite3 prompt and output, in case you want to cut and paste them as a single block (but still start sqlite3 before you paste these in, bestie):

ALTER TABLE book ADD created TIMESTAMP;
ALTER TABLE book ADD updated TIMESTAMP;
UPDATE book SET created = DATETIME('NOW'), updated = DATETIME('NOW');
SELECT * FROM book;

This will modify the books table to include the two new fields and populate those fields with the current time. 🕐

Update DBIx::Class to Automatically Handle the Datetime Columns 💫

Next, we should re-run the DBIC helper to update the Result Classes with the new fields:

$ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
    create=static components=TimeStamp dbi:SQLite:myapp.db \
    on_connect_do="PRAGMA foreign_keys = ON"
 exists "/home/catalyst/dev/MyApp/script/../lib/MyApp/Model"
 exists "/home/catalyst/dev/MyApp/script/../t"
Dumping manual schema for MyApp::Schema to directory /home/catalyst/dev/MyApp/script/../lib ...
Schema dump completed.
 exists "/home/catalyst/dev/MyApp/script/../lib/MyApp/Model/DB.pm"

Notice that we modified our use of the helper slightly: we told it to include the DBIx::Class::TimeStamp in the load_components line of the Result Classes. 🎀

If you open lib/MyApp/Schema/Result/Book.pm in your editor you should see that the created and updated fields are now included in the call to add_columns(). However — also notice that the many_to_many relationships we manually added below the "# DO NOT MODIFY..." line were automatically preserved. Bestie behaviour fr fr. 🫶

While we've got lib/MyApp/Schema/Result/Book.pm open, let's update it with some additional information so DBIC automatically handles the updating of these two fields for us. Insert the following code at the bottom of the file (it must be below the "# DO NOT MODIFY..." line and above the 1; on the last line):

#
# Enable automatic date handling
#
__PACKAGE__->add_columns(
    "created",
    { data_type => 'timestamp', set_on_create => 1 },
    "updated",
    { data_type => 'timestamp', set_on_create => 1, set_on_update => 1 },
);

This will override the definition for these fields that Schema::Loader placed at the top of the file. And bestie, the set_on_create and set_on_update options are literally doing the most — they make DBIx::Class automatically update the timestamps in these columns whenever a row is created or modified. Iconic. ✨

Lowkey important note: adding the lines above will cause the development server to automatically restart if you are running it with the -r option. So the development server is smart enough to restart not only for code under the MyApp/Controller/, MyApp/Model/, and MyApp/View/ directories, but also under other directions such as our "external DBIC model" in MyApp/Schema/. But also — and this is the funny part — it's smart enough to not restart when you edit your .tt2 files under root/. We love a server with discernment. 💅

Then enter the following URL into your web browser:

http://localhost:3000/books/url_create/TCPIP_Illustrated_Vol-2/5/4

You should get the same "Book Created" screen we saw earlier. However, if you now use the sqlite3 command-line tool to dump the books table, you will see that the new book we added has an appropriate date and time entered for it (see the last line in the listing below):

$ sqlite3 myapp.db "select * from book"
1|CCSP SNRS Exam Certification Guide|5|2010-02-16 04:15:45|2010-02-16 04:15:45
2|TCP/IP Illustrated, Volume 1|5|2010-02-16 04:15:45|2010-02-16 04:15:45
3|Internetworking with TCP/IP Vol.1|4|2010-02-16 04:15:45|2010-02-16 04:15:45
4|Perl Cookbook|5|2010-02-16 04:15:45|2010-02-16 04:15:45
5|Designing with Web Standards|5|2010-02-16 04:15:45|2010-02-16 04:15:45
9|TCP/IP Illustrated, Vol 3|5|2010-02-16 04:15:45|2010-02-16 04:15:45
10|TCPIP_Illustrated_Vol-2|5|2010-02-16 04:18:42|2010-02-16 04:18:42

Notice in the debug log that the SQL DBIC generated has changed to incorporate the datetime logic:

INSERT INTO book ( created, rating, title, updated ) VALUES ( ?, ?, ?, ? ):
'2010-02-16 04:18:42', '5', 'TCPIP_Illustrated_Vol-2', '2010-02-16 04:18:42'
INSERT INTO book_author ( author_id, book_id ) VALUES ( ?, ? ): '4', '10'

🌸 Create a ResultSet Class 🌸

Okay so an often overlooked but extremely powerful feature of DBIC is that it allows you to supply your own subclasses of DBIx::Class::ResultSet. And why do we care? Because this can be used to pull complex and unsightly "query code" out of your controllers and encapsulate it in a method of your ResultSet Class. These "canned queries" in your ResultSet Class can then be invoked via a single call, resulting in much cleaner and easier to read controller code (or View code, if that's where you want to call it). No cap, it's giving glow-up for your codebase. 🦋

To illustrate the concept with a fairly simple example, let's create a method that returns books added in the last 10 minutes. Start by making a directory where DBIx::Class will look for our ResultSet Class:

$ mkdir lib/MyApp/Schema/ResultSet

Then open lib/MyApp/Schema/ResultSet/Book.pm and enter the following:

package MyApp::Schema::ResultSet::Book;

use strict;
use warnings;
use base 'DBIx::Class::ResultSet';

=head2 created_after

A predefined search for recently added books

=cut

sub created_after {
    my ($self, $datetime) = @_;

    my $date_str = $self->result_source->schema->storage
                          ->datetime_parser->format_datetime($datetime);

    return $self->search({
        created => { '>' => $date_str }
    });
}

1;

Then add the following method to the lib/MyApp/Controller/Books.pm:

=head2 list_recent

List recently created books

=cut

sub list_recent :Chained('base') :PathPart('list_recent') :Args(1) {
    my ($self, $c, $mins) = @_;

    # Retrieve all of the book records as book model objects and store in the
    # stash where they can be accessed by the TT template, but only
    # retrieve books created within the last $min number of minutes
    $c->stash(books => [$c->model('DB::Book')
                            ->created_after(DateTime->now->subtract(minutes => $mins))]);

    # Set the TT template to use.  You will almost always want to do this
    # in your action methods (action methods respond to user input in
    # your controllers).
    $c->stash(template => 'books/list.tt2');
}

Now try different values for the "minutes" argument (the final number value) using the URL http://localhost:3000/books/list_recent/_#_ in your browser. For example, this would list all books added in the last fifteen minutes:

http://localhost:3000/books/list_recent/15

Depending on how recently you added books, you might want to try a higher or lower value for the minutes. Go on, play with it, it's fun. 🎀

---

🔗 Chaining ResultSets 🔗

One of the most helpful and powerful features in DBIx::Class is that it allows you to "chain together" a series of queries (and note that this has nothing to do with the "Chained Dispatch" for Catalyst that we were discussing earlier — different thing entirely, don't get it twisted 🙈). Because each ResultSet method returns another ResultSet, you can take an initial query and immediately feed that into a second query (and so on for as many queries you need). And here's the slay part: no matter how many ResultSets you chain together, the database itself will not be hit until you use a method that attempts to access the data. Lazy in the best way possible. And because this technique carries over to the ResultSet Class feature we implemented in the previous section for our "canned search", we can combine the two capabilities. 💀✨

For example, let's add an action to our "Books" controller that lists books that are both recent and have "TCP" in the title. Open up lib/MyApp/Controller/Books.pm and add the following method:

=head2 list_recent_tcp

List recently created books

=cut

sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
    my ($self, $c, $mins) = @_;

    # Retrieve all of the book records as book model objects and store in the
    # stash where they can be accessed by the TT template, but only
    # retrieve books created within the last $min number of minutes
    # AND that have 'TCP' in the title
    $c->stash(books => [
            $c->model('DB::Book')
                ->created_after(DateTime->now->subtract(minutes => $mins))
                ->search({title => {'like', '%TCP%'}})
        ]);

    # Set the TT template to use.  You will almost always want to do this
    # in your action methods (action methods respond to user input in
    # your controllers).
    $c->stash(template => 'books/list.tt2');
}

To try this out, enter the following URL into your browser:

http://localhost:3000/books/list_recent_tcp/100

And you should get a list of books added in the last 100 minutes that contain the string "TCP" in the title. However, if you look at all books within the last 100 minutes, you should get a longer list (again, you might have to adjust the number of minutes depending on how recently you added books to your database):

http://localhost:3000/books/list_recent/100

Take a look at the DBIC_TRACE output in the development server log for the first URL and you should see something similar to the following:

SELECT me.id, me.title, me.rating, me.created, me.updated FROM book me
WHERE ( ( title LIKE ? AND created > ? ) ): '%TCP%', '2010-02-16 02:49:32'

However — and this is the vibe check — let's not pollute our controller code with this raw "TCP" query, because it would be cleaner to encapsulate that code in a method on our ResultSet Class. To do this, open lib/MyApp/Schema/ResultSet/Book.pm and add the following method:

=head2 title_like

A predefined search for books with a 'LIKE' search in the string

=cut

sub title_like {
    my ($self, $title_str) = @_;

    return $self->search({
        title => { 'like' => "%$title_str%" }
    });
}

We defined the search string as $title_str to make the method more flexible. Now update the "list_recent_tcp" method in lib/MyApp/Controller/Books.pm to match the following (we have replaced the ->search line with the ->title_like line shown here — the rest of the method should be the same):

=head2 list_recent_tcp

List recently created books

=cut

sub list_recent_tcp :Chained('base') :PathPart('list_recent_tcp') :Args(1) {
    my ($self, $c, $mins) = @_;

    # Retrieve all of the book records as book model objects and store in the
    # stash where they can be accessed by the TT template, but only
    # retrieve books created within the last $min number of minutes
    # AND that have 'TCP' in the title
    $c->stash(books => [
            $c->model('DB::Book')
                ->created_after(DateTime->now->subtract(minutes => $mins))
                ->title_like('TCP')
        ]);

    # Set the TT template to use.  You will almost always want to do this
    # in your action methods (action methods respond to user input in
    # your controllers).
    $c->stash(template => 'books/list.tt2');
}

Try out the "list_recent_tcp" and "list_recent" URLs as we did above. They should work just the same, but our code is obviously cleaner and more modular, while also being more flexible at the same time. Main character code, honestly. 👑

---

🧚 Adding Methods to Result Classes 🧚

In the previous two sections we saw a good example of how we could use DBIx::Class ResultSet Classes to clean up our code for an entire query (for example, our "canned searches" that filtered the entire query). We can do a similar improvement when working with individual rows as well. So — whereas the ResultSet construct is used in DBIC to correspond to an entire query, the Result Class construct is used to represent a row. Therefore, we can add row-specific "helper methods" to our Result Classes stored in lib/MyApp/Schema/Result/. For example, open lib/MyApp/Schema/Result/Author.pm and add the following method (as always, it must be above the closing "1;"):

#
# Row-level helper methods
#
sub full_name {
    my ($self) = @_;

    return $self->first_name . ' ' . $self->last_name;
}

This will allow us to conveniently retrieve both the first and last name for an author in one shot. Now open root/src/books/list.tt2 and change the definition of "tt_authors" from this:

...
  [% tt_authors = [ ];
     tt_authors.push(author.last_name) FOREACH author = book.authors %]
...

to:

...
  [% tt_authors = [ ];
     tt_authors.push(author.full_name) FOREACH author = book.authors %]
...

(Only author.last_name was changed to author.full_name — the rest of the file should remain the same.) 🫶

Now go point your browser at the standard book list URL:

http://localhost:3000/books/list

The "Author(s)" column is gonna have both the first and the last name now. 💖 And here's the pretty part — because that concatenation logic got tucked away inside our Result Class, the code inside our TT template stays nice and clean (remember, bestie: we want templates to be as close to pure HTML markup as possible, that's the whole vibe). Obviously this capability gets even more useful as you use it to yank even more complicated row-specific logic out of your templates — it's giving glow-up. ✨

🎀 Moving Complicated View Code to the Model 🎀

Okay so the last section showed us how to use a Result Class method to print the full names of the authors without adding extra code to our view — but ngl it still left us with a pretty ugly mess (peep root/src/books/list.tt2):

...
<td>
    [% # NOTE: See Chapter 4 for a better way to do this!                      -%]
    [% # First initialize a TT variable to hold a list.  Then use a TT FOREACH -%]
    [% # loop in 'side effect notation' to load just the last names of the     -%]
    [% # authors into the list. Note that the 'push' TT vmethod does not print -%]
    [% # a value, so nothing will be printed here.  But, if you have something  -%]
    [% # in TT that does return a method and you don't want it printed, you    -%]
    [% # can: 1) assign it to a bogus value, or 2) use the CALL keyword to     -%]
    [% # call it and discard the return value.                                 -%]
    [% tt_authors = [ ];
       tt_authors.push(author.full_name) FOREACH author = book.authors %]
    [% # Now use a TT 'virtual method' to display the author count in parens   -%]
    [% # Note the use of the TT filter "| html" to escape dangerous characters -%]
    ([% tt_authors.size | html %])
    [% # Use another TT vmethod to join & print the names & comma separators   -%]
    [% tt_authors.join(', ') | html %]
</td>
...

Let's mash together some of the techniques from earlier in this section to clean it up. 🌸 First up: let's add a method to our Book Result Class that returns the number of authors for a book. Open up lib/MyApp/Schema/Result/Book.pm and drop in this method:

=head2 author_count

Return the number of authors for the current book

=cut

sub author_count {
    my ($self) = @_;

    # Use the 'many_to_many' relationship to fetch all of the authors for the current
    # and the 'count' method in DBIx::Class::ResultSet to get a SQL COUNT
    return $self->authors->count;
}

Next, let's add a method that returns a list of authors for a book to that same lib/MyApp/Schema/Result/Book.pm file:

=head2 author_list

Return a comma-separated list of authors for the current book

=cut

sub author_list {
    my ($self) = @_;

    # Loop through all authors for the current book, calling all the 'full_name'
    # Result Class method for each
    my @names;
    foreach my $author ($self->authors) {
        push(@names, $author->full_name);
    }

    return join(', ', @names);
}

That method loops through each author, calling the full_name Result Class method we added to lib/MyApp/Schema/Result/Author.pm in the prior section. 🫶

Using these two methods, we can simplify our TT code. Open root/src/books/list.tt2 and update the "Author(s)" table cell so it matches this:

...
<td>
    [% # Print count and author list using Result Class methods -%]
    ([% book.author_count | html %]) [% book.author_list | html %]
</td>
...

And even though most of the code we removed was literally just comments, the overall effect is dramatic — because our view code is so simple now, we don't need giant comments to clue people in to the gist of it. The view code is self-documenting and readable enough that you could probably get by with zero comments at all, no cap. 💅 All of the "complex" work is happening in our Result Class methods (and honestly, because we broke the code into nice modular chunks, the Result Class code is hardly something you'd even call complex).

So like we saw in this section: always strive to keep your view AND controller code as simple as possible by pulling code out into your model objects. Because DBIx::Class can be easily extended in so many ways, it's an excellent way to accomplish this objective. It'll make your code cleaner, easier to write, less error-prone, and easier to debug and maintain. Periodt. 👑

Before you wrap this section, hit Refresh in your browser… the output should be exactly the same even though the backend code got trimmed way down. 🦋

You can jump to the next chapter of the tutorial here: Authentication

---

👑 AUTHOR 👑

Kennedy Clark, "hkclark@gmail.com"

Feel free to contact the author for any errors or suggestions, but the best way to report issues is via the CPAN RT Bug system at <https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.

Copyright 2006-2011, Kennedy Clark, under the Creative Commons Attribution Share-Alike License Version 3.0 (<https://creativecommons.org/licenses/by-sa/3.0/us/>).

---

That's a wrap, bestie! 🎀 This page came to you from perl v5.42.0, dated 2024-03-23, and it's filed under Catalys...sicCRUD(3) — go forth and slay your CRUD. 💜✨