Sequel Orderable Plugin¶ ↑

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

Load the plugin into the model:

plugin :orderable

Given:

DB.create_table :items do
  primary_key :id
  varchar :name
  int :position
end

class Item < Sequel::Model(:items)
  plugin :orderable
end

item = Item[1]

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

You can scope the position field by another field.

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

DB.create_table :items do
  primary_key :id
  varchar :name
  int :user_id
  int :pos
end

class Item < Sequel::Model(:items)
  plugin :orderable, :field => :pos, :scope => :user_id
end

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

# Input: irb
require 'sequel'
require 'sequel_orderable'
require 'sequel/extensions/pretty_table' # for pretty prints

DB = Sequel.sqlite

DB.create_table :items do
  primary_key :id
  varchar :name
  int :position
end

class Item < Sequel::Model(:items)
  plugin :orderable
end

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
=> #<Item @values={:name=>"alice", :position=>3, :id=>1}>

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

>> Item[:name => "darwin"].move_to_top
=> #<Item @values={:name=>"darwin", :position=>1, :id=>4}>

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

>> Item[:name => "alice"].next
=> #<Item @values={:name=>"charlie", :position=>4, :id=>3}>

>> Item[:name => "bob"].prev
=> #<Item @values={:name=>"darwin", :position=>1, :id=>4}>

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

Copyright © 2007 Sharon Rosner, Wayne E. Seguin, Aman Gupta, Adrian Madrid

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