Sequel Orderable Plugin

Allows for model instances to be part of an ordered list, based on a ‘position’ field in the database.

Basic Usage

Load the plugin into the model:

is :orderable

Given:

class Item < Sequel::Model(:items)

set_schema do
  primary_key :id
  varchar :name
  int :position
end
is :orderable, :field => :position

end

item = Item

The plugin provides access to the previous and next item in the list

item.next
item.prev

And methods to change the position of an item (and update affected items accordingly)

item.move_to(new_position)
item.move_to_top
item.move_to_bottom
item.move_up
item.move_down

Scoping

You can scope the position field by another field.

For example, to allow each user to have their own a distinct orderable list:

class UserItem < Sequel::Model(:items)

set_schema do
  primary_key :id
  varchar :name
  int :user_id
  int :pos
end
is :orderable, :field => :pos, :scope => :user_id

end

All the defined methods will operate within the ‘user_id’ field’s scope.

Examples

# Input: irb require “sequel”

DB = Sequel.sqlite class Item < Sequel::Model(:items)

set_schema do
  primary_key :id
  varchar :name
  int :position
end
is :orderable, :field => :position

end

Item.create_table! Item.create :name => “alice”, :position => 2 Item.create :name => “bob”, :position => 1 Item.create :name => “charlie”, :position => 4 Item.create :name => “darwin”, :position => 3

Item.print

Item[:name => “alice”].move_down Item.print Item[:name => “darwin”].move_to_top Item.print Item[:name => “alice”].next Item.print Item[:name => “bob”].prev Item.print Item[:name => “darwin”].move_to(3) Item.print Item[:name => “bob”].move_to_bottom Item.print

# Output >> Item.print --——--------- |id|name |position| --——--------- | 2|bob | 1| | 1|alice | 2| | 4|darwin | 3| | 3|charlie| 4| --——---------

> nil

>> Item[:name => “alice”].move_down

> :position=>3

>> Item.print --——--------- |id|name |position| --——--------- | 2|bob | 1| | 4|darwin | 2| | 1|alice | 3| | 3|charlie| 4| --——---------

> nil

>> Item[:name => “darwin”].move_to_top

> :position=>1

>> Item.print --——--------- |id|name |position| --——--------- | 4|darwin | 1| | 2|bob | 2| | 1|alice | 3| | 3|charlie| 4| --——---------

> nil

>> Item[:name => “alice”].next

> #<Item:0x119dbc8 @values=:name=>“charlie”, :id=>3, newfalse

>> Item.print --——--------- |id|name |position| --——--------- | 4|darwin | 1| | 2|bob | 2| | 1|alice | 3| | 3|charlie| 4| --——---------

> nil

>> Item[:name => “bob”].prev

> #<Item:0x1184bb4 @values=:name=>“darwin”, :id=>4, newfalse

>> Item.print --——--------- |id|name |position| --——--------- | 4|darwin | 1| | 2|bob | 2| | 1|alice | 3| | 3|charlie| 4| --——---------

> nil

>> Item[:name => “darwin”].move_to(3)

> :position=>3

>> Item.print --——--------- |id|name |position| --——--------- | 2|bob | 1| | 1|alice | 2| | 4|darwin | 3| | 3|charlie| 4| --——---------

> nil

>> Item[:name => “bob”].move_to_bottom

> :position=>4

>> Item.print --——--------- |id|name |position| --——--------- | 1|alice | 1| | 4|darwin | 2| | 3|charlie| 3| | 2|bob | 4| --——---------

> nil