Sequenced is a simple gem that generates scoped sequential IDs for
ActiveRecord models. This gem provides an acts_as_sequenced macro that
automatically assigns a unique, sequential ID to each record. The sequential ID is
not a replacement for the database primary key, but rather adds another way to
retrieve the object without exposing the primary key.
It's generally a bad practice to expose your primary keys to the world in your URLs. However, it is often appropriate to number objects in sequence (in the context of a parent object).
For example, given a Question model that has many Answers, it makes sense to number answers sequentially for each individual question. You can achieve this with Sequenced in one line of code:
class Question < ActiveRecord::Base
has_many :answers
end
class Answer < ActiveRecord::Base
belongs_to :question
acts_as_sequenced scope: :question_id
endAdd the gem to your Gemfile:
gem 'sequenced'
Install the gem with bundler:
bundle install
To add a sequential ID to a model, first add an integer column called
sequential_id to the model (or you many name the column anything you
like and override the default). For example:
rails generate migration add_sequential_id_to_answers sequential_id:integer
rake db:migrate
Then, call the acts_as_sequenced macro in your model class:
class Answer < ActiveRecord::Base
belongs_to :question
acts_as_sequenced scope: :question_id
endThe scope option can be any attribute, but will typically be the foreign
key of an associated parent object. You can even scope by multiple columns
for polymorphic relationships:
class Answer < ActiveRecord::Base
belongs_to :questionable, :polymorphic => true
acts_as_sequenced scope: [:questionable_id, :questionable_type]
endIf you want to promote or demote a sequencable entity, call
*your_model_object*.promote(:up) (or) *your_model_object*.promote(:down)
If you manually change the sequence id's and if you want to reassign the ids in same order starting from the same start_at value with which the sequence has been generated with (which is mostly 1).
*your_model_object*.sanitize_sequence
You can access all the members of the same scope in ascending order like this.
*<any_one_record_from_the_scope>*.getScopedRecords###Get the top member of the sequence You can access the top(smallest sequential_id) member of a scoped sequence like this
*<any_one_record_from_the_scope>*.get_sequence_top###Get the bottom member of the sequence You can access the bottom(largest sequential_id) member of a scoped sequence like this
*<any_one_record_from_the_scope>*.get_sequence_bottomBy default, Sequenced uses the sequential_id column and assumes it already
exists. If you wish to store the sequential ID in different integer column,
simply specify the column name with the column option:
acts_as_sequenced scope: :question_id, column: :my_sequential_idBy default, Sequenced begins sequences with 1. To start at a different
integer, simply set the start_at option:
acts_as_sequenced start_at: 1000You may also pass a lambda to the start_at option:
acts_as_sequenced start_at: lambda { |r| r.computed_start_value }For optimal performance, it's a good idea to index the sequential ID column on sequenced models.
If you'd like to skip generating a sequential ID under certain conditions,
you may pass a lambda to the skip option:
acts_as_sequenced skip: lambda { |r| r.score == 0 }Suppose you have a question model that has many answers. This example demonstrates how to use Sequenced to enable access to the nested answer resource via its sequential ID.
# app/models/question.rb
class Question < ActiveRecord::Base
has_many :answers
end
# app/models/answer.rb
class Answer < ActiveRecord::Base
belongs_to :question
acts_as_sequenced scope: :question_id
# Automatically use the sequential ID in URLs
def to_param
self.sequential_id
end
end
# config/routes.rb
resources :questions
resources :answers
end
# app/controllers/answers_controller.rb
class AnswersController < ApplicationController
before_filter :load_question
before_filter :load_answer, only: [:show, :edit, :update, :destroy]
private
def load_question
@question = Question.find(params[:question_id])
end
def load_answer
@answer = @question.answers.where(:sequential_id => params[:id]).first
end
endNow, answers are accessible via their sequential IDs:
http://example.com/questions/5/answers/1 # Good
instead of by their primary keys:
http://example.com/questions/5/answer/32454 # Bad
Copyright © 2012-2013 Derrick Reimer
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