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Handel::Manual::Cookbook::AddingColumns
Adding columns in Handel

Handel::Manual::Cookbook::AddingColumns - Adding columns in Handel


NAME

Handel::Manual::Cookbook::AddingColumns - Adding columns in Handel


DESCRIPTION

The methods below outline the steps necessary to add columns to the default install of Handel. The steps below generally apply to customizing most storage options, including removing columns, adding constraints, etc.


GOOD

If you need a quick fix in a script or want to alter all instances of Handel objects within the same process, you can simple add a column to the desired classes storage using add_columns in the Handel::Storage manpage.


    #!/usr/bin/perl -w

    use strict;

    use warnings;

    use Handel::Cart;

    

    Handel::Cart->storage->add_columns('custom');

    Handel::Cart->create_accessors;

    

    

    my $carts = Handel::Cart->search;

    print $carts->count;

    

    while (my $cart = $carts->next) {

        print $cart->custom, "\n";

    };


BETTER

The example above gets the job done with a minimal amount of code. But if you're on shared server with other people using Handel, you're going to get a nasty phone call when every one discovers their stuff has an extra field in it.

The better, more polite approach is to make your own custom classes and use [ab]use them instead.


    package My::Cart;

    use strict;

    use warnings;

    use base qw/Handel::Cart/;

    

    __PACKAGE__->item_class('My::Cart::Item');

    __PACKAGE__->storage->add_columns('custom');

    __PACKAGE__->create_accessors;

    

    1;

You don't have to subclass both the cart and items classes, but for the sake of good practice, there's no reason not to if you've gone this far.


    package My::Cart::Item;

    use strict;

    use warnings;

    use base qw/Handel::Cart::Item/;

    

    1;

Then in your script, use you're cart instead.


    #!/usr/bin/perl -w

    use strict;

    use warnings;

    use My::Cart;

    

    my $carts = My::Cart->search;

    print $carts->count;

    

    while (my $cart = $carts->next) {

        print $cart->custom, "\n";

    };


BEST

The two approaches above have one potential issue: they assume that the current classes will always use the default storage. If you add columns using only the column name, that won't be an issue. If you add columns using the DBIx::Class \%column_info syntax, you will have a problem if the new storage class doesn't understand the syntax.


    package My::Cart;

    use strict;

    use warnings;

    

    use base qw/Handel::Cart/;

    __PACKAGE__->storage_class('Future::Storage::XML');

    

    # this line goes boom!

    # don't know how to add column 'HASH(0x2254b8)'

    __PACKAGE__->storage->add_columns('foo' => {

        data_type   => 'varchar',

        size        => 50,

        is_nullable => 1

    });

    

    1;

This is a potential problem when setting any storage class option from within the interface classes that uses it. To help abstract the storage specifics away from the interface classes that use them, you should go the extra mile and declare custom storage classes. I did mention that it's a 'framework' right? :-)

Create Cart and Item Storage Classes

First we need to create custom storage classes for the Cart and Item interface classes.


    package My::Storage::Cart;

    use strict;

    use warnings;

    use base qw/Handel::Storage::DBIC::Cart/;

    

    __PACKAGE__->item_storage_class('My::Storage::Cart::Item');

    

    __PACKAGE__->add_columns('foo' => {

        data_type   => 'varchar',

        size        => 50,

        is_nullable => 1

    });

    

    1;

    

    package My::Storage::Cart::Item;

    use strict;

    use warnings;

    use base qw/Handel::Storage::DBIC::Cart::Item/;

    

    1;

Create Cart and Item Classes


    package My::Cart;

    use strict;

    use warnings;

    use base qw/Handel::Cart/;

    

    __PACKAGE__->item_class('My::Cart::Item');

    

    # No storage changes in here

    # The storage class takes care of adding the column

    __PACKAGE__->storage_class('My::Storage::Cart');

    __PACKAGE__->create_accessors;

    

    1;

    

    package My::Cart::Item;

    use strict;

    use warnings;

    use base qw/Handel::Cart::Item/;

    

    __PACKAGE__->storage_class('My::Storage::Cart::Item');

    __PACKAGE__->create_accessors;

    

    1;

Code Away Merrill


    #!/usr/bin/perl -w

    use strict;

    use warnings;

    use My::Cart;

    

    my $carts = My::Cart->search;

    print $carts->count;

    

    while (my $cart = $carts->next) {

        print $cart->custom, "\n";

    };

Now that we've pushed the add column magic down into the storage class, My::Cart is blissfully unaware of any changes that storage class needs to make in order to add a column:


    package My::Storage::Cart;

    use strict;

    use warnings;

    use base qw/Handel::Storage::DBIC::Cart/;

    

    __PACKAGE__->item_storage_class('My::Storage::Cart::Item');

    

    __PACKAGE__->add_columns([qw/foo varchar 50 nullable/]);

    

    1;


SEE ALSO

the Handel::Storage manpage, the Handel::Storage::DBIC manpage, the Handel::Storage::DBIC::Cart manpage, the Handel::Storage::DBIC::Cart::Item manpage


AUTHOR


    Christopher H. Laco

    CPAN ID: CLACO

    claco@chrislaco.com

    http://today.icantfocus.com/blog/
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