NAME
DBIx::Iterator - Query your database using iterators and save memory
VERSION
version 0.0.2
SYNOPSIS
# Create an iterator for a simple DBI query
my $db = DBIx::Iterator->new( DBI->connect('...') );
my $it = $db->query("SELECT id, name FROM person");
while ( my $row = $it->() ) {
say $row->{'id'} . ": " . $row->{'name'};
# Do something with $row...
}
# We have a basic class here that knows nothing about iterators
package Person;
use Moose;
has 'id' => ( is => 'ro', isa => 'Int' );
has 'name' => ( is => 'ro', isa => 'Str' );
sub label {
my ($self) = @_;
return $self->id . ": " . $self->name;
}
# Then we have a role that knows how to create instances
# from iterators
package FromIterator;
use Moose::Role;
sub new_from_iterator {
my ($self, $it) = @_;
return sub {
my $row = $it->();
return unless defined $row;
return $self->new($row);
}
}
# Then we apply the role to the Person class and use
# our plain database iterator that produces hashes to
# now create Person instances instead.
package main;
use Moose::util qw(apply_all_roles);
my $p = apply_all_roles('Person', 'FromIterator');
my $it = $p->new_from_iterator(
$db->query("SELECT * FROM person")
);
while ( my $person = $it->() ) {
say $person->label;
# Do something with $person...
}
DESCRIPTION
Iterators are a nice way to perform operations on large datasets without
having to keep all of the data you're working on in memory at the same
time. Most people have experience with iterators already from working
with filehandles. They are basically iterators hidden behind a somewhat
odd syntax. This module gives you the same way of executing database
queries.
The trivial example at the start of the synopsis is not very different
from using "fetchrow_hashref" in DBI directly to retrieve your database
rows. But when we look at the second example we can start to see how it
allows much cleaner separation of concerns without having to modify the
core class (Person) to support iterators or database interaction at all.
For more information about iterators and how they can work for you, have
a look at chapter 4 in the book Higher-Order Perl mentioned below. It is
free to download and highly recommended.
METHODS
new($dbh)
Creates a new iterator factory connected to the specified database
handle.
dbh
Returns the database handle provided to new().
prepare($query)
Asks the database engine to parse the query and return a statement
object that can be used to execute the query with optional parameters.
query($query, @placeholder_values)
Executes the query with the optional placeholder values. Returns a code
reference you can execute until it is exhausted. If called in list
context, it will also return a reference to the statement object itself.
The iterator returns exactly what "fetchrow_hashref" in DBI returns.
When the iterator is exhausted it will return undef.
SEE ALSO
* Higher-Order Perl by Mark Jason Dominus, page 163-173
<
http://hop.perl.plover.com/>
* Iterator
SEMANTIC VERSIONING
This module uses semantic versioning concepts from <
http://semver.org/>.
SUPPORT
Perldoc
You can find documentation for this module with the perldoc command.
perldoc DBIx::Iterator
Websites
The following websites have more information about this module, and may
be of help to you. As always, in addition to those websites please use
your favorite search engine to discover more resources.
* MetaCPAN
A modern, open-source CPAN search engine, useful to view POD in HTML
format.
<
http://metacpan.org/release/DBIx-Iterator>
* Search CPAN
The default CPAN search engine, useful to view POD in HTML format.
<
http://search.cpan.org/dist/DBIx-Iterator>
* RT: CPAN's Bug Tracker
The RT ( Request Tracker ) website is the default bug/issue tracking
system for CPAN.
<
http://rt.cpan.org/NoAuth/Bugs.html?Dist=DBIx-Iterator>
* AnnoCPAN
The AnnoCPAN is a website that allows community annotations of Perl
module documentation.
<
http://annocpan.org/dist/DBIx-Iterator>
* CPAN Ratings
The CPAN Ratings is a website that allows community ratings and
reviews of Perl modules.
<
http://cpanratings.perl.org/d/DBIx-Iterator>
* CPAN Forum
The CPAN Forum is a web forum for discussing Perl modules.
<
http://cpanforum.com/dist/DBIx-Iterator>
* CPANTS
The CPANTS is a website that analyzes the Kwalitee ( code metrics )
of a distribution.
<
http://cpants.perl.org/dist/overview/DBIx-Iterator>
* CPAN Testers
The CPAN Testers is a network of smokers who run automated tests on
uploaded CPAN distributions.
<
http://www.cpantesters.org/distro/D/DBIx-Iterator>
* CPAN Testers Matrix
The CPAN Testers Matrix is a website that provides a visual overview
of the test results for a distribution on various Perls/platforms.
<
http://matrix.cpantesters.org/?dist=DBIx-Iterator>
* CPAN Testers Dependencies
The CPAN Testers Dependencies is a website that shows a chart of the
test results of all dependencies for a distribution.
<
http://deps.cpantesters.org/?module=DBIx::Iterator>
Bugs / Feature Requests
Please report any bugs or feature requests by email to
"bug-dbix-iterator at rt.cpan.org", or through the web interface at
<
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBIx-Iterator>. You will
be automatically notified of any progress on the request by the system.
Source Code
The code is open to the world, and available for you to hack on. Please
feel free to browse it and play with it, or whatever. If you want to
contribute patches, please send me a diff or prod me to pull from your
repository :)
<
http://github.com/robinsmidsrod/DBIx-Iterator>
git clone git://github.com/robinsmidsrod/DBIx-Iterator.git
AUTHOR
Robin Smidsrød <
[email protected]>
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Robin Smidsrød.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
