Class::DBI::Plugin::Pager - paged queries for CDBI
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.
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 );
# $pager isa Data::Page
# @cds contains the CDs just for the current page
- import
- Loads the "pager" method into the CDBI app.
- pager( [$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 is "LimitOffset".
- 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" or
"search_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 to "retrieve_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 a
"make_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 a "FETCH" 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 passing
"syntax => 'LimitXY'" to a method call, or call
"set_syntax" directly.
Any driver not in the supported or unsupported lists defaults to
LimitOffset.
Any additions to the supported and unsupported lists gratefully
received.
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?
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).
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.
The source code for this module is hosted on GitHub
<
https://github.com/majesticcpan/class-dbi-plugin-pager>. Feel free to
fork the repository and submit pull requests!
SQL::Abstract, Data::Page, Class::DBI::Plugin::AbstractCount, Class::Accessor,
Class::Data::Inheritable, Carp.
Class::DBI::Pager does a similar job, but retrieves the entire results set into
memory before chopping out the page you want.
Please report all bugs via the CPAN Request Tracker at
<
http://rt.cpan.org/NoAuth/Bugs.html?Dist=Class-DBI-Plugin-Pager>.
Copyright 2004-2012 by David Baird.
Copyright 2012 Nikolay S. "
[email protected]"
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
David Baird