has-bit-field allows you to use one attribute of an object to store a bit field which stores the boolean state for multiple flags.
Add the gem to your Gemfile.
To use this with Active Record, you would first require this gem in
Now in one of your models, you define a bit field like this:
class Person < ActiveRecord::Base extend HasBitField has_bit_field :bit_field, :likes_ice_cream, :plays_golf, :watches_tv, :reads_books end
This means that your database will have an integer column called
bit_field which will hold the actual bit field. This will generate getter and setter methods for each of the fields. It will also generate a method that has
_bit as a suffix which will give you the decimal value of the bit that that field is represented by in the bit field. Also there will be a named scope for that field, as well as a named scope prefixed with
not_, if class you are adding the bit field to responds to
named_scope. You can use it like this:
$ script/console Loading development environment (Rails 2.3.2) p =>> p = Person.new => #<Person id: nil, bit_field: nil, created_at: nil, updated_at: nil> >> p.likes_ice_cream = "true" => "true" >> p.plays_golf = 1 => 1 >> p.save => true >> p = Person.find(p.id) => #<Person id: 1, bit_field: 3, created_at: "2009-07-18 03:04:06", updated_at: "2009-07-18 03:04:06"> >> p.likes_ice_cream? => true >> p.reads_books? => false >> Person.plays_golf_bit => 4 >> p = Person.likes_ice_cream.first => #<Person id: 1, bit_field: 3, created_at: "2009-07-18 03:04:06", updated_at: "2009-07-18 03:04:06">
One of the great advantages of this approach is that it is easy to add additional flags as your application evolves without the overhead of adding new table columns since a single integer will be able to store at least 31 boolean flags. A simple amendment to the model will create the new flag on the existing integer column 'on-the-fly'. However, the order of the flags is vitally important and you should only ever add new flags on the end.
class Person < ActiveRecord::Base extend HasBitField has_bit_field :bit_field, :likes_ice_cream, :plays_golf, :watches_tv, :reads_books, :nut_allergy end
The new flag will be evaluated as false for existing rows on the database table until their values are explicitly set. Be careful with the peanuts!
Another gotcha to be aware of is when combining a bit field with Active Record's
validates_acceptance_of. When you call
validates_acceptance_of, if there is no database column, Active Record will define an
attr_accessor for that boolean field. If you have already defined the bit field, this will clobber those methods. Also, you need to set the value it's looking for to
true instead of the default of
"1". So here's an example of how to use it:
class Person < ActiveRecord::Base extend HasBitField validates_acceptance_of :read_books, :message => "You must agree to read", :accept => true has_bit_field :bit_field, :likes_ice_cream, :plays_golf, :watches_tv, :reads_books end
Copyright (c) 2009 Paul Barry. See LICENSE for details.