AutocompleteFor

This plugin implements model-side logic for autocompleting belongs_to associations. It handles validations, autocompleting the same association via different fields (say name or login) and the ability to specify a custom finder block.

It works out-of-the-box with existing front-end autocompletion solutions because all it does is set the value of the belongs_to association based on an attribute that can be set directly or via update_attributes (see examples below.)

Example

class Author < ActiveRecord::Base
  # has a login and open_id column
end

class Post < ActiveRecord::Base
  belongs_to :author

  # set the author_login field to autocomplete by author login
  autocomplete_for :author, :login do
    self.author = Author.find(:first, :conditions => {:login => @author_login})
  end

  # set the author_open_id field to autocomplete by author open_id
  autocomplete_for :author, :open_id do
    self.author = Author.find(:first, :conditions => {:open_id => @author_open_id})
  end
end

Using autocomplete_for in your models to set belongs_to associations:

author = Author.create! :login => 'baz'
post = Post.create! :author_login => 'baz'    # automatically finds the author with the login 'baz'
puts post.author.login                        # will output 'baz'

Errors are generated automatically if the given information does not correspond to a valid model:

author = Author.create! :login => 'baz'
post = Post.create :author_login => 'quux'
puts post.errors[:author_login]               # will print an error message