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+# ActsAsDigestedOn [![Build Status](https://travis-ci.org/milk1000cc/acts_as_digested_on.svg)](https://travis-ci.org/milk1000cc/acts_as_digested_on)
+
+acts_as_digested_on is a gem for Rails 3 and Rails 4.
+
+This sets the digested value before validation and validates uniqueness of the digested value.
+
+If you use this gem for Rails 2, see rails-2 branch.
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+    gem 'acts_as_digested_on'
+
+And then execute:
+
+    $ bundle
+
+Or install it yourself as:
+
+    $ gem install acts_as_digested_on
+
+## Usage
+
+```ruby
+# db/migrate/20090706000000_create_articles.rb
+class CreateArticles < ActiveRecord::Migration
+  def self.up
+    create_table :articles do |t|
+      t.text :url       # any type is ok
+      t.string :digest  # this is sha-1 hex digest field of url value
+      ...
+    end
+
+    add_index :articles, :digest, :unique => true  # you can add index on digest field
+  end
+
+  def self.down
+    drop_table :articles
+  end
+end
+
+# app/models/article.rb
+class Article < ActiveRecord::Base
+  acts_as_digested_on :url  # please add this
+  ...
+end
+
+# this means
+class Article < ActiveRecord::Base
+  validates_uniqueness_of :digest
+  before_validation :set_digest
+
+  def generate_digest
+    Digest::SHA1.hexdigest "--#{ url.to_s }--"
+  end
+
+  private
+  def set_digest
+    self.digest = generate_digest
+  end
+  ...
+end
+```
+
+## Examples
+
+```ruby
+acts_as_digested_on :url, :unique => false
+
+acts_as_digested_on :url, :digest_column => :url_digest
+
+acts_as_digested_on [:url, :salt]
+
+acts_as_digested_on :url, :scope => :site_id
+
+Article.new(:url => 'http://example.com').generate_digest
+```
+
+## Contributing
+
+1. Fork it ( https://github.com/milk1000cc/acts_as_digested_on/fork )
+2. Create your feature branch (`git checkout -b my-new-feature`)
+3. Commit your changes (`git commit -am 'Add some feature'`)
+4. Push to the branch (`git push origin my-new-feature`)
+5. Create a new Pull Request