dm-is-list¶ ↑

DataMapper plugin for creating and organizing lists.

Install the dm-is-list gem.

$ (sudo)? gem install dm-is-list

Download or clone dm-is-list from Github.

$ cd /path/to/dm-is-list

$ rake install            # will install dm-is-list

# enter your password at the prompt, if required
$ password ...

To start using this gem, just require dm-is-list in your app.

require 'dm-core'         # must be required first
require 'dm-is-list'

Lets say we have a User class, and we want to give users the possibility of having their own todo-lists.

class User
  include DataMapper::Resource

  property :id,   Serial
  property :name, String

  has n, :todos
end

class Todo
  include DataMapper::Resource

  property :id,    Serial
  property :title, String
  property :done,  DateTime

  belongs_to :user

  # here we define that this should be a list, scoped on :user_id
  is :list, :scope => :user_id  # you may also pass in multiple properties, eg [ :user_id, :title ]
end

Once we have our Users and Lists, we might want to work with…

Any list item can be moved around within the same list easily through the #move method.

There are number of convenient vectors that help you move items around within the list.

item = Todo.get(1)
other = Todo.get(2)

item.move(:highest)          # moves to top of list.
item.move(:lowest)           # moves to bottom of list.
item.move(:top)              # moves to top of list.
item.move(:bottom)           # moves to bottom of list.
item.move(:up)               # moves one up (:higher and :up is the same) within the scope.
item.move(:down)             # moves one up (:lower and :down is the same) within the scope.
item.move(:to => position)   # moves item to a specific position.
item.move(:above => other)   # moves item above the other item.*
item.move(:below => other)   # moves item above the other item.*

# * won't move if the other item is in another scope. (should this be enabled?)

The list will act as intelligently as possible and keep positions in a logical running order.

NOTE! VERY IMPORTANT!

If you set the position manually, and then save, the list will NOT reorganize itself.

item.position = 3      # setting position manually
item.save              # the item will now have position 3, but the list may have two items with the same position.

# alternatively
item.update(:position => 3)    # sets the position manually, but does not reorganize the list positions.

You should therefore always use the item.move(N) syntax instead.

item.move(3)          # does the same as above, but in one call AND *reorganizes* the list.

<hr>

Hold On!

dm-is-list used to work with item.position = 1 type syntax. Why this change?

The main reason behind this change was that the previous version of dm-is-list created a LOT of extra SQL queries in order to support the manual updating of position, and as a result had a quite a few bugs/issues, which have been fixed in this version.

The other reason is that I couldn’t work out how to keep the functionality without adding the extra queries. But perhaps you can ?

<hr>

See “Batch Changing Positions” below for information on how to change the positions on a whole list.

When you move items between scopes, the list will try to work with your intentions.

Move the item from list to new list and add the item to the bottom of that list.

item.user_id                 # => 1
item.move_to_list(10)        # => the scope id ie User.get(10).id

# results in...
item.user_id                 # => 10
item.position                # => < bottom of the list >

Move the item from list to new list and add at the position given.

item.user_id                 # => 1
item.move_to_list(10, 2)     # => the scope id ie User.get(10).id,  position => 2

# results in...
item.user_id                 # => 10
item.position                # => 2

A common scenario when working with lists is the sorting of a whole list via something like JQuery’s sortable() functionality.
(Think re-arranging the order of Todo’s according to priority or something similar)

The most SQL query efficient way of changing the positions is:

sort_order = [5,4,3,2,1]              # list from AJAX request..

items = Todo.all(:user => @u1)        # loads all 5 items in the list

items.each{ |item| item.update(:position => sort_order.index(item.id) + 1) }   # remember the +1 since array's are indexed from 0

The above code will result in something like these queries.

# SELECT "id", "title", "position", "user_id" FROM "todos" WHERE "user_id" = 1 ORDER BY "position"
# UPDATE "todos" SET "position" = 5 WHERE "id" = 1
# UPDATE "todos" SET "position" = 4 WHERE "id" = 2
# UPDATE "todos" SET "position" = 2 WHERE "id" = 4
# UPDATE "todos" SET "position" = 1 WHERE "id" = 5

Remember! Your sort order list has to be the same length as the found items in the list, or your loop will fail.

You can also use this version, but it will create upto 5 times as many SQL queries. :(

sort_order = ['5','4','3','2','1']    # list from AJAX request..

items = Todo.all(:user => @u1)        # loads all 5 items in the list

items.each{ |item| item.move(sort_order.index(item.id).to_i + 1) }   # remember the +1 since array's are indexed from 0

The above code will result in something like these queries:

#  SELECT "id", "title", "position", "user_id" FROM "todos" WHERE "user_id" = 1 ORDER BY "position"

#  SELECT "id", "title", "position", "user_id" FROM "todos" WHERE "user_id" = 1 ORDER BY "position" DESC LIMIT 1
#  SELECT "id" FROM "todos" WHERE "user_id" = 1 AND "id" IN (1, 2, 3, 4, 5) AND "position" BETWEEN 1 AND 5 ORDER BY "position"
#  UPDATE "todos" SET "position" = "position" + -1 WHERE "user_id" = 1 AND "position" BETWEEN 1 AND 5
#  SELECT "id", "position" FROM "todos" WHERE "id" IN (1, 2, 3, 4, 5) ORDER BY "id"
#  UPDATE "todos" SET "position" = 5 WHERE "id" = 1

#  SELECT "id", "title", "position", "user_id" FROM "todos" WHERE "user_id" = 1 ORDER BY "position" DESC LIMIT 1
#  SELECT "id" FROM "todos" WHERE "user_id" = 1 AND "id" IN (1, 2, 3, 4, 5) AND "position" BETWEEN 1 AND 4 ORDER BY "position"
#  UPDATE "todos" SET "position" = "position" + -1 WHERE "user_id" = 1 AND "position" BETWEEN 1 AND 4
#  SELECT "id", "position" FROM "todos" WHERE "id" IN (2, 3, 4, 5) ORDER BY "id"
#  UPDATE "todos" SET "position" = 4 WHERE "id" = 2

#  ...

As you can see it will also do the job, but will be more expensive.

As I said above, for a better understanding of this gem/plugin, make sure you study the ‘dm-is-list/spec/integration/list_spec.rb’ tests.

If something is not behaving intuitively, it is a bug, and should be reported. Report it here: datamapper.lighthouseapp.com/

• None at the moment. Or do you think something is missing?

• Fork the project.

• Make your feature addition or bug fix.

• Add tests for it. This is important so we don’t break it in a future version unintentionally.

• Commit, do not mess with rakefile, version, or history.

  • (if you want to have your own version, that is fine but bump version in a commit by itself we can ignore when we pull)

• Send us a pull request. Bonus points for topic branches.

Copyright © 2011 Sindre Aarsaether. Released under the MIT License.

See LICENSE for details.

Credit also goes to these contributors.