module Sequel::Plugins::List

  1. lib/sequel/plugins/list.rb

The list plugin allows for model instances to be part of an ordered list, based on a position field in the database. It can either consider all rows in the table as being from the same list, or you can specify scopes so that multiple lists can be kept in the same table.

Basic Example:

class Item < Sequel::Model(:items)
  plugin :list # will use :position field for position
  plugin :list, :field=>:pos # will use :pos field for position

item = Item[1]

# Get the next or previous item in the list

# Modify the item's position, which may require modifying other items in
# the same list


You can provide a :scope option to scope the list. This option can be a symbol or array of symbols specifying column name(s), or a proc that accepts a model instance and returns a dataset representing the list the object is in.

For example, if each item has a user_id field, and you want every user to have their own list:

Item.plugin :list, :scope=>:user_id

Note that using this plugin modifies the order of the model's dataset to sort by the position and scope fields. Also note that this plugin is subject to race conditions, and is not safe when concurrent modifications are made to the same list.

Additionally, note that unlike ruby arrays, the list plugin assumes that the first entry in the list has position 1, not position 0.

Copyright © 2007-2010 Sharon Rosner, Wayne E. Seguin, Aman Gupta, Adrian Madrid, Jeremy Evans


Public Class

  1. configure

Public Class methods

configure (model, opts = OPTS)

Set the position_field and scope_proc attributes for the model, using the :field and :scope options, respectively. The :scope option can be a symbol, array of symbols, or a proc that accepts a model instance and returns a dataset representing the list. Also, modify the model dataset's order to order by the position and scope fields.

[show source]
# File lib/sequel/plugins/list.rb, line 57
def self.configure(model, opts = OPTS)
  model.position_field = opts[:field] || :position
  model.dataset = model.dataset.order_prepend(model.position_field)
  model.scope_proc = case scope = opts[:scope]
  when Symbol
    model.dataset = model.dataset.order_prepend(scope)
    proc{|obj| obj.model.where(scope=>obj.send(scope))}
  when Array
    model.dataset = model.dataset.order_prepend(*scope)
    proc{|obj| obj.model.where({|s| [s, obj.get_column_value(s)]})}