Why not adopt me?
NAME
Class::DBI::Plugin::Pager - paged queries for CDBI
DESCRIPTION
Adds a pager method to your class that can query using SQL::Abstract where clauses, and limit the number of rows returned to a specific subset.
SYNOPSIS
package CD;
use base 'Class::DBI';
use Class::DBI::Plugin::AbstractCount; # pager needs this
use Class::DBI::Plugin::Pager;
# or to use a different syntax
# use Class::DBI::Plugin::Pager::RowsTo;
__PACKAGE__->set_db(...);
# in a nearby piece of code...
use CD;
# see SQL::Abstract for how to specify the query
my $where = { ... };
my $order_by => [ qw( foo bar ) ];
# bit by bit:
my $pager = CD->pager;
$pager->per_page( 10 );
$pager->page( 3 );
$pager->where( $where );
$pager->order_by( $order_by );
$pager->set_syntax( 'RowsTo' );
my @cds = $pager->search_where;
# or all at once
my $pager = CD->pager( $where, $order_by, 10, 3 );
my @cds = $pager->search_where;
# or
my $pager = CD->pager;
my @cds = $pager->search_where( $where, $order_by, 10, 3 );
# $pager isa Data::Page
# @cds contains the CDs just for the current page
METHODS
- import
-
Loads the
pager
method into the CDBI app. - pager( [$where, [$abstract_attr]], [$order_by], [$per_page], [$page], [$syntax] )
-
Also accepts named arguments:
where => $where, abstract_attr => $attr, order_by => $order_by, per_page => $per_page, page => $page, syntax => $syntax
Returns a pager object. This subclasses Data::Page.
Note that for positional arguments,
$abstract_attr
can only be passed if preceded by a$where
argument.$abstract_attr
can contain the$order_by
setting (just as in SQL::Abstract).- configuration
-
The named arguments all exist as get/set methods.
- where
-
A hashref specifying the query. See SQL::Abstract.
- abstract_attr
-
A hashref specifying extra options to be passed through to the SQL::Abstract constructor.
- order_by
-
Single column name or arrayref of column names for the ORDER BY clause. Defaults to the primary key(s) if not set.
- per_page
-
Number of results per page.
- page
-
The pager will retrieve results just for this page. Defaults to 1.
- syntax
-
Change the way the 'limit' clause is constructed. See
set_syntax
. Default isLimitOffset
.
- search_where
-
Retrieves results from the pager. Accepts the same arguments as the
pager
method. - retrieve_all
-
Convenience method, generates a WHERE clause that matches all rows from the table.
Accepts the same arguments as the
pager
orsearch_where
methods, except that no WHERE clause should be specified.Note that the argument parsing routine called by the
pager
method cannot cope with positional arguments that lack a WHERE clause, so either use named arguments, or the 'bit by bit' approach, or pass the arguments directly toretrieve_all
. - set_syntax( [ $name || $class || $coderef ] )
-
Changes the syntax used to generate the
limit
or other phrase that restricts the results set to the required page.The syntax is implemented as a method called on the pager, which can be queried to provide the
$rows
and$offset
parameters (see the subclasses included in this distribution).- $class
-
A class with a
make_limit
method. - $name
-
Name of a class in the
Class::DBI::Plugin::Pager::
namespace, which has amake_limit
method. - $coderef
-
Will be called as a method on the pager object, so receives the pager as its argument.
- (no args)
-
Called without args, will default to
LimitOffset
, which causes Class::DBI::Plugin::Pager::LimitOffset to be used.
- auto_set_syntax
-
This is called automatically when you call
pager
, and attempts to set the syntax automatically.If you are using a subclass of the pager, this method will not be called.
Will
die
if using Oracle or DB2, since there is no simple syntax for limiting the results set. DB2 has aFETCH
keyword, but that seems to apply to a cursor and I don't know if there is a cursor available to the pager. There should probably be others to add to the unsupported list.Supports the following drivers:
DRIVER CDBI::P::Pager subclass my %supported = ( pg => 'LimitOffset', mysql => 'LimitOffset', # older versions need LimitXY sqlite => 'LimitOffset', # or LimitYX sqlite2 => 'LimitOffset', # or LimitYX interbase => 'RowsTo', firebird => 'RowsTo', );
Older versions of MySQL should use the LimitXY syntax. You'll need to set it manually, either by
use CDBI::P::Pager::LimitXY
, or by passingsyntax => 'LimitXY'
to a method call, or callset_syntax
directly.Any driver not in the supported or unsupported lists defaults to LimitOffset.
Any additions to the supported and unsupported lists gratefully received.
SUBCLASSING
The 'limit' syntax can be set by using a subclass, e.g.
use Class::DBI::Plugin::Pager::RowsTo;
instead of setting at runtime. A subclass looks like this:
package Class::DBI::Plugin::Pager::RowsTo;
use base 'Class::DBI::Plugin::Pager';
sub make_limit {
my ( $self ) = @_;
my $offset = $self->skipped;
my $rows = $self->entries_per_page;
my $last = $rows + $offset;
return "ROWS $offset TO $last";
}
1;
You can omit the use base
and switch syntax by calling $pager->set_syntax( 'RowsTo' )
. Or you can leave in the use base
and still say $pager->set_syntax( 'RowsTo' )
, because in this case the class is require
d and the import
in the base class doesn't get called. Or something. At any rate, It Works.
The subclasses implement the following LIMIT syntaxes:
- Class::DBI::Plugin::Pager::LimitOffset
-
LIMIT $rows OFFSET $offset
This is the default if your driver is not in the list of known drivers.
This should work for PostgreSQL, more recent MySQL, SQLite, and maybe some others.
- Class::DBI::Plugin::LimitXY
-
LIMIT $offset, $rows
Older versions of MySQL.
- Class::DBI::Plugin::LimitYX
-
LIMIT $rows, $offset
SQLite.
- Class::DBI::Plugin::RowsTo
-
ROWS $offset TO $offset + $rows
InterBase, also FireBird, maybe others?
TODO
I've only used this on an older version of MySQL. Reports of this thing working (or not) elsewhere would be useful.
It should be possible to use set_sql
to build the complex queries required by some databases to emulate LIMIT (see notes in source).
CAVEATS
This class can't implement the subselect mechanism required by some databases to emulate the LIMIT phrase, because it only has access to the WHERE clause, not the whole SQL statement. At the moment.
Each query issues two requests to the database - the first to count the entire result set, the second to retrieve the required subset of results. If your tables are small it may be quicker to use Class::DBI::Pager.
The order_by
clause means the database has to retrieve (internally) and sort the entire results set, before chopping out the requested subset. It's probably a good idea to have an index on the column(s) used to order the results. For huge tables, this approach to paging may be too inefficient.
DEPENDENCIES
SQL::Abstract, Data::Page, Class::DBI::Plugin::AbstractCount, Class::Accessor, Class::Data::Inheritable, Carp.
SEE ALSO
Class::DBI::Pager does a similar job, but retrieves the entire results set into memory before chopping out the page you want.
BUGS
Please report all bugs via the CPAN Request Tracker at http://rt.cpan.org/NoAuth/Bugs.html?Dist=Class-DBI-Plugin-Pager.
COPYRIGHT AND LICENSE
Copyright 2004 by David Baird.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
AUTHOR
David Baird, cpan@riverside-cms.co.uk