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=head1 NAME

Catalyst::Manual::Tutorial::BasicCRUD - Catalyst Tutorial - Part 3: Basic CRUD


=head1 OVERVIEW

This is B<Part 3 of 9> for the Catalyst tutorial.

L<Tutorial Overview|Catalyst::Manual::Tutorial>

=over 4

=item 1

L<Introduction|Catalyst::Manual::Tutorial::Intro>

=item 2

L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics>

=item 3

B<Basic CRUD>

=item 4

L<Authentication|Catalyst::Manual::Tutorial::Authentication>

=item 5

L<Authorization|Catalyst::Manual::Tutorial::Authorization>

=item 6

L<Debugging|Catalyst::Manual::Tutorial::Debugging>

=item 7

L<Testing|Catalyst::Manual::Tutorial::Testing>

=item 8

L<AdvancedCRUD|Catalyst::Manual::Tutorial::AdvancedCRUD>

=item 9

L<Appendicies|Catalyst::Manual::Tutorial::Appendicies>

=back



=head1 DESCRIPTION

This part of the tutorial builds on the fairly primitive application
created in Part 2 to add basic support for Create, Read, Update, and
Delete (CRUD) of C<Book> objects.  Note that the 'list' function in Part
2 already implements the Read portion of CRUD (although Read normally
refers to reading a single object; you could implement full read
functionality using the techniques introduced below).  This section will
focus on the Create and Delete aspects of CRUD.  More advanced
capabilities, including full Update functionality, will be addressed in
Part 8.

B<TIP>: Note that all of the code for this part of the tutorial can be
pulled from the Catalyst Subversion repository in one step with the
following command:

    svn checkout http://dev.catalyst.perl.org/repos/Catalyst/trunk/examples/Tutorial@###
    IMPORTANT: Does not work yet.  Will be completed for final version.


=head1 FORMLESS SUBMISSION

Our initial attempt at object creation will utilize the "URL arguments"
feature of Catalyst (we will employ the more common form-based
submission in the sections that follow).


=head2 Include a Create Action in the Books Controller

Edit C<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 @_
        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('MyAppDB::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 in the view
        $c->stash->{book} = $book;
    
        # This is a hack to disable XSUB processing in Data::Dumper
        # (it's used in the view).  This is a work-around for a bug in
        # the interaction of some versions or Perl, Data::Dumper & DBIC.
        # You won't need this if you aren't using Data::Dumper (or if
        # you are running DBIC 0.06001 or greater), but adding it doesn't 
        # hurt anything either.
        $Data::Dumper::Useperl = 1;
    
        # Set the TT template to use
        $c->stash->{template} = 'books/create_done.tt2';
    }

Notice that Catalyst takes "extra slash-separated information" from the
URL and passes it as arguments in C<@_>.  The C<url_create> action then
uses a simple call to the DBIC C<create> method to add the requested
information to the database (with a separate call to
C<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.


=head2 Include a Template for the C<url_create> Action:

Edit C<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 for      -%]
    [% # root/lib/site/html and root/lib/site/header).  Note that META on    -%]
    [% # simple strings (e.g., no variable interpolation).                   -%]
    [% META title = 'Book Created' %]
    
    [% # Output information about the record that was added.  Note use  -%]
    [% # of 'first' to only list the first author (if > 1 author).  TT  -%] 
    [% # v2.15 has an issue that requires                               -%]
    [% # 'book.authors.list.first.value.last_name' vs. the shorter      -%]
    [% # 'book.authors.first.last_name' in prior versions.              -%]
    <p>Added book '[% book.title %]' 
    by '[% book.authors.list.first.value.last_name %]'
    with a rating of [% book.rating %].</p>
    
    [% # Provide a link back to the list page                                    -%]
    [% # 'uri_for()' builds a full URI; e.g., 'http://localhost:3000/books/list' -%]
    <p><a href="[% Catalyst.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 C<USE> directive allows access to a variety of plugin modules (TT
plugins, that is, not Catalyst plugins) to add extra functionality to
the base TT capabilities.  Here, the plugin allows L<Data::Dumper>
"pretty printing" of objects and variables.  Other than that, the rest
of the code should be familiar from the examples in Part 2.

B<IMPORTANT NOTE> As mentioned earlier, the C<MyApp::View::TT.pm> view
class created by TTSite redefines the name used to access the Catalyst
context object in TT templates from the usual C<c> to C<Catalyst>.

=head2 Try the C<url_create> Feature

If the application is still running from before, use C<Ctrl-C> to kill
it. Then restart the server:

    $ script/myapp_server.pl

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

B<TIP>: You can use C<script/myapp_server.pl -r> to have the development
server auto-detect changed files and reload itself (if your browser acts
odd, you should also try throwing in a C<-k>).  If you make changes to
the TT templates only, you do not need to reload the development server
(only changes to "compiled code" such as Controller and Model C<.pm>
files require a reload).

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.  You should also see the following DBIC debug messages displayed
in the development server log messages:

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

If you then click the "Return to list" link, you should find that there
are now six books shown (if necessary, Shift-Reload your browser at the
C</books/list> page).


=head1 MANUALLY BUILDING A CREATE FORM

Although the C<url_create> action in the previous step does begin to
reveal the power and flexibility of both Catalyst and DBIC, it's
obviously not a very realistic example of how users should be expected
to enter data.  This section begins to address that concern.


=head2 Add Method to Display The Form

Edit C<lib/MyApp/Controller/Books.pm> and add the following method:

    =head2 form_create
    
    Display form to collect information for book to create
    
    =cut
    
    sub form_create : Local {
        my ($self, $c) = @_;
    
        # Set the TT template to use
        $c->stash->{template} = 'books/form_create.tt2';
    }

This action simply invokes a view containing a book creation form.

=head2 Add a Template for the Form

Open C<root/src/books/form_create.tt2> in your editor and enter:

    [% META title = 'Manual Form Book Create' -%]
    
    <form method="post" action="[% Catalyst.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>

Note that we have specified the target of the form data as
C<form_create_do>, the method created in the section that follows.

=head2 Add Method to Process Form Values and Update Database

Edit C<lib/MyApp/Controller/Books.pm> and add the following method to
save the form information to the databse:

    =head2 form_create_do
    
    Take information from form and add to database
    
    =cut
    
    sub form_create_do : Local {
        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('MyAppDB::Book')->create({
                title   => $title,
                rating  => $rating,
            });
        # Handle relationship with author
        $book->add_to_book_authors({author_id => $author_id});
    
        # Store new model object in stash
        $c->stash->{book} = $book;
    
        # Avoid Data::Dumper issue mentioned earlier
        # You can probably omit this    
        $Data::Dumper::Useperl = 1;
    
        # Set the TT template to use
        $c->stash->{template} = 'books/create_done.tt2';
    }


=head2 Test Out The Form

If the application is still running from before, use C<Ctrl-C> to kill
it.  Then restart the server:

    $ script/myapp_server.pl

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 be forwarded to the same
C<create_done.tt2> template seen in earlier examples.  Finally, click
"Return to list" to view the full list of books.

B<Note:> Having the user enter the primary key ID for the author is
obviously crude; we will address this concern with a drop-down list in
Part 8.

=head1 A SIMPLE DELETE FEATURE

Turning out attention to the delete portion of CRUD, this section
illustrates some basic techniques that can be used to remove information
from the database.


=head2 Include a Delete Link in the List

Edit C<root/src/books/list.tt2> and update it to the following (two
sections have changed: 1) the additional '<th>Links</th>' table header,
and 2) the four lines for the Delete link near the bottom).

    [% # This is a TT comment.  The '-' at the end "chomps" the newline.  You won't -%]
    [% # see this "chomping" in your browser because HTML ignores blank lines, but  -%]
    [% # it WILL eliminate a blank line if you view the HTML source.  It's purely   -%]
    [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
    
    [% # Provide a title to root/lib/site/header -%]
    [% META title = 'Book List' -%]
    
    <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>
          [% # 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 we are making a bogus assignment to -%]
          [% # the 'xx' vbl to avoid printing the size of the list after each push.  -%]
          [% tt_authors = [ ];
             xx = tt_authors.push(author.last_name) FOREACH author = book.authors %]
          [% # Now use a TT 'virtual method' to display the author count             -%]
          ([% tt_authors.size %])
          [% # Use another TT virtual method to join the names with comma separators -%]
          [% tt_authors.join(', ') %]
        </td>
        <td>
          [% # Add a link to delete a book %]
          <a href="[% Catalyst.uri_for('delete/') _ book.id %]">Delete</a>
        </td>
      </tr>
    [% END -%]
    </table>

The additional code is obviously designed to add a new column to the
right side of the table with a C<Delete> "button" (for simplicity, links
will be used instead of full HTML buttons).

=head2 Add a Delete Action to the Controller

Open C<lib/MyApp/Controller/Books.pm> in your editor and add the
following method:

    =head2 delete 
    
    Delete a book
        
    =cut
    
    sub delete : Local {
        # $id = primary key of book to delete
        my ($self, $c, $id) = @_;
    
        # Search for the book and then delete it
        $c->model('MyAppDB::Book')->search({id => $id})->delete_all;
    
        # 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');
    }

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.

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
notification to the user as the normal list view is rendered.

The C<delete> action uses the context C<forward> method to return the
user to the book list.  The C<detach> method could have also been used.
Whereas C<forward> I<returns> to the original action once it is
completed, C<detach> does I<not> return.  Other than that, the two are
equivalent.

Another alternative to C<forward> would be to use
C<$c-E<gt>response-E<gt>redirect($c-E<gt>uri_for('/books/list'))>.  The
C<forward> and C<redirect> operations differ in several important
respects that stem from the fact that redirects cause the client browser
to issue an entirely new HTTP request.  In doing so, this results in a
new URL showing in the browser window.  And, because the stash
information is reset for every request, the "Book deleted" message would
not be displayed.


=head2 Try the Delete Feature

If the application is still running from before, use C<Ctrl-C> to kill
it.  Then restart the server:

    $ script/myapp_server.pl

Then point your browser to L<http://localhost:3000/books/list> and click
the "Delete" link next to "TCPIP_Illustrated_Vol-2".  A green "Book
deleted" status message should display at the top of the page, along
with a list of the six remaining books.


=head1 AUTHOR

Kennedy Clark, C<hkclark@gmail.com>

Please report any errors, issues or suggestions to the author.  The
most recent version of the Catlayst Tutorial can be found at
L<http://dev.catalyst.perl.org/repos/Catalyst/trunk/Catalyst-Runtime/lib/Catalyst/Manual/Tutorial/>.

Copyright 2006, Kennedy Clark, under Creative Commons License
(L<http://creativecommons.org/licenses/by-nc-sa/2.5/>).