DBIx::Class::Ordered - Modify the position of objects in an ordered list.
Create a table for your ordered data.
CREATE TABLE items ( item_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL, position INTEGER NOT NULL ); # Optional: group_id INTEGER NOT NULL
In your Schema or DB class add Ordered to the top of the component list.
__PACKAGE__->load_components(qw( Ordered ... ));
Specify the column that stores the position number for each row.
package My::Item; __PACKAGE__->position_column('position'); __PACKAGE__->grouping_column('group_id'); # optional
Thats it, now you can change the position of your objects.
#!/use/bin/perl use My::Item; my $item = My::Item->create({ name=>'Matt S. Trout' }); # If using grouping_column: my $item = My::Item->create({ name=>'Matt S. Trout', group_id=>1 }); my $rs = $item->siblings(); my @siblings = $item->siblings(); my $sibling; $sibling = $item->first_sibling(); $sibling = $item->last_sibling(); $sibling = $item->previous_sibling(); $sibling = $item->next_sibling(); $item->move_previous(); $item->move_next(); $item->move_first(); $item->move_last(); $item->move_to( $position );
This module provides a simple interface for modifying the ordered position of DBIx::Class objects.
All of the move_* methods automatically update the rows involved in the query. This is not configurable and is due to the fact that if you move a record it always causes other records in the list to be updated.
__PACKAGE__->position_column('position');
Sets and retrieves the name of the column that stores the positional value of each record. Default to "position".
__PACKAGE__->grouping_column('group_id');
This method specified a column to limit all queries in this module by. This effectively allows you to have multiple ordered lists within the same table.
my $rs = $item->siblings(); my @siblings = $item->siblings();
Returns either a result set or an array of all other objects excluding the one you called it on.
my $sibling = $item->first_sibling();
Returns the first sibling object, or 0 if the first sibling is this sibliing.
my $sibling = $item->last_sibling();
Return the last sibling, or 0 if the last sibling is this sibling.
my $sibling = $item->previous_sibling();
Returns the sibling that resides one position back. Undef is returned if the current object is the first one.
my $sibling = $item->next_sibling();
Returns the sibling that resides one position foward. Undef is returned if the current object is the last one.
$item->move_previous();
Swaps position with the sibling on position previous in the list. 1 is returned on success, and 0 is returned if the objects is already the first one.
$item->move_next();
Swaps position with the sibling in the next position. 1 is returned on success, and 0 is returned if the object is already the last in the list.
$item->move_first();
Moves the object to the first position. 1 is returned on success, and 0 is returned if the object is already the first.
$item->move_last();
Moves the object to the very last position. 1 is returned on success, and 0 is returned if the object is already the last one.
$item->move_to( $position );
Moves the object to the specified position. 1 is returned on success, and 0 is returned if the object is already at the specified position.
Overrides the DBIC insert() method by providing a default position number. The default will be the number of rows in the table +1, thus positioning the new record at the last position.
Overrides the DBIC delete() method by first moving the object to the last position, then deleting it, thus ensuring the integrity of the positions.
These methods are used internally. You should never have the need to use them.
This method returns a name=>value pare for limiting a search by the collection column. If the collection column is not defined then this will return an empty list.
Unique indexes and constraints on the position column are not supported at this time. It would be make sense to support them, but there are some unexpected database issues that make this hard to do. The main problem from the author's view is that SQLite (the DB engine that we use for testing) does not support ORDER BY on updates.
If a position is not specified for an insert than a position will be chosen based on COUNT(*)+1. But, it first selects the count then inserts the record. The space of time between select and insert introduces a race condition. To fix this we need the ability to lock tables in DBIC. I've added an entry in the TODO about this.
Be careful when issueing move_* methods to multiple objects. If you've pre-loaded the objects then when you move one of the objects the position of the other object will not reflect their new value until you reload them from the database.
There are times when you will want to move objects as groups, such as changeing the parent of several objects at once - this directly conflicts with this problem. One solution is for us to write a ResultSet class that supports a parent() method, for example. Another solution is to somehow automagically modify the objects that exist in the current object's result set to have the new position value.
Aran Deltac <bluefeet@cpan.org>
You may distribute this code under the same terms as Perl itself.
To install DBIx::Class, copy and paste the appropriate command in to your terminal.
cpanm
cpanm DBIx::Class
CPAN shell
perl -MCPAN -e shell install DBIx::Class
For more information on module installation, please visit the detailed CPAN module installation guide.