How do I process then return something in Moose?

dr_death has asked for the wisdom of the Perl Monks concerning the following question:

Hello all,

I am pretty new to OOP programming and am trying to learn how to use Moose and I cant seem to find an example/explanation of what I need to do, although I am learning a lot reading through trying to find it.

What I am trying to do is create a new object like below and then have that return an ID from a DB.

get_id->new( email => 'test@test.com' );

I have something like the below already;

has 'email' => (
    is        =>    'rw',
    isa        =>    'Str',
    required     =>    1,
    clearer        =>    'clear_email',
    predicate    =>    'has_email',
);
[download]

I've seen 'default => sub', but I'm not entirely sure if it's appropriate or how the inheritance works using it.

Is there someway I can call a sub or method and have it return the ID? If so, could you please tell me where I can find it in the documentation?

Thanks for your help!

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Re: How do I process then return something in Moose? by 1nickt (Canon) on Feb 07, 2017 at 12:57 UTC
Hi dr_death, I personally use Moo rather than Moose as I find the latter has lots of power tools I never need. However, I believe the answer is mostly the same for the two systems. You probably want to use `default` or `builder` as described at http://search.cpan.org/~ether/Moose-2.2004/lib/Moose/Manual/Attributes.pod#Default_and_builder_methods. Since you'll presumably need one of the other attributes to use in the DB query, you'll probably have to make the attribute lazy and use `builder`. Something like: `has 'email' => ( is => 'rw', isa => 'Str', lazy => 1, builder => '_lookup_email', ); sub _lookup_email { my $self = shift; return $self->_dbh->selectall_array( 'select email from users where name = ?', {}, $self->name, )->[0]; );` [download] Obviously you'll have to supply the DB connection, error handling if the email is not found, etc. Also note that the `Moo[se]` Type libraries should be able to provide an email address type, so your `isa` could be `email` or similar and the value will be checked. Edit: On re-reading I see that you maybe want to supply the email address and return the DB ID after adding a record? If so, just change the builder sub to do what you want! Hope this helps! The way forward always starts with a minimal test.	[reply] [d/l] [select]

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Re: How do I process then return something in Moose?
by 1nickt (Canon) on Feb 07, 2017 at 12:57 UTC

Hi dr_death,

I personally use Moo rather than Moose as I find the latter has lots of power tools I never need. However, I believe the answer is mostly the same for the two systems. You probably want to use default or builder as described at http://search.cpan.org/~ether/Moose-2.2004/lib/Moose/Manual/Attributes.pod#Default_and_builder_methods. Since you'll presumably need one of the other attributes to use in the DB query, you'll probably have to make the attribute lazy and use builder. Something like:

has 'email' => (
    is        => 'rw',
    isa       => 'Str',
    lazy      => 1,
    builder   => '_lookup_email',
);

sub _lookup_email {
    my $self = shift;
    return $self->_dbh->selectall_array(
        'select email from users where name = ?',
        {},
        $self->name,
    )->[0];
);
[download]

Moo[se]

isa

email

Edit: On re-reading I see that you maybe want to supply the email address and return the DB ID after adding a record? If so, just change the builder sub to do what you want!

Hope this helps!

The way forward always starts with a minimal test.

[reply]
[d/l]
[select]