SimpleEnum - unobtrusive enum-like fields for ActiveRecord

A Rails plugin which brings easy-to-use enum-like functionality to ActiveRecord models.

Note: a recent search on github for ‘enum` turned out, that there are many, many similar solutions. Yet, none seem to provide so many options, but I may be biased ;)

Quick start

Add this to a model:

class User < ActiveRecord::Base
  as_enum :gender, {:female => 1, :male => 0}
end

Then create the new column using migrations:

class AddGenderColumnToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :gender_cd, :integer
  end

  def self.down
    remove_column :users, :gender_cd
  end
end

Done. Now it’s possible to pull some neat tricks on the new column, yet the original db column (gender_cd) is still intact and not touched by any fancy metaclass or similar.

jane = User.new
jane.gender = :female
jane.female?   # => true
jane.male?     # => false
jane.gender    # => :female
jane.gender_cd # => 1

Easily switch to another value using the bang methods.

joe = User.new
joe.male!     # => :male
joe.gender    # => :male
joe.gender_cd # => 0

There are even some neat tricks at class level, which might be useful when creating queries, displaying option elements or similar:

User.genders            # => { :male => 0, :female => 1 }
User.genders(:male)     # => 0, same as User.male
User.female             # => 1
User.genders.female     # => 1, same as User.female or User.genders(:female)

Wait, there’s more!

Too tired of always adding the integer values? Try:
```
class User < ActiveRecord::Base
  as_enum :status, [:deleted, :active, :disabled] # translates to :deleted => 0, :active => 1, :disabled => 2
end
```
Disclaimer: if you ever decide to reorder this array, beaware that any previous mapping is lost. So it’s recommended to create mappings (that might change) using hashes instead of arrays. For stuff like gender it might be probably perfectly fine to use arrays though.
Maybe you’ve columns named differently than the proposed {column}_cd naming scheme, feel free to use any column name by providing an option:
```
class User < ActiveRecord::Base
  as_enum :gender, [:male, :female], :column => 'sex'
end
```
To make it easier to create dropdowns with values use:
```
<%= select(:user, :gender, User.genders.keys) %>
```
It’s possible to validate the internal enum values, just like any other ActiveRecord validation:
```
class User < ActiveRecord::Base
  as_enum :gender, [:male, :female]
  validates_as_enum :gender
end
```
All common options like :if, :unless, :allow_nil and :message are supported, because it just works within the standard validates_each-loop. This validation method does not check the value of user.gender, but instead the value of @user.gender_cd.
If the shortcut methods (like <symbol>?, <symbol>! or Klass.<symbol>) conflict with something in your class, it’s possible to define a prefix:
```
class User < ActiveRecord::Base
  as_enum :gender, [:male, :female], :prefix => true
end

jane = User.new :gender => :female
jane.gender_female? # => true
User.gender_female  # => 1, this also works on the class methods
```
The :prefix option not only takes a boolean value as an argument, but instead can also be supplied a custom prefix (i.e. any string or symbol), so with :prefix => 'foo' all shortcut methods would look like: foo_<symbol>... Note: if the :slim => true is defined, this option has no effect whatsoever (because no shortcut methods are generated).

Sometimes it might be useful to disable the generation of the shortcut methods (<symbol>?, <symbol>! and Klass.<symbol>), to do so just add the option :slim => true:

class User < ActiveRecord::Base
  as_enum :gender, [:male, :female], :slim => true
end

jane = User.new :gender => :female
jane.female? # => throws NoMethodError: undefined method `female?' 
User.male    # => throws NoMethodError: undefined method `male'

Yet the setter and getter for gender, as well as the User.genders methods are still available, only all shortcut methods for each of the enumeration values are not generated.

It’s also possible to set :slim => :class which only disables the generation of any class-level shortcut method, because those are also available via the enhanced enumeration hash:

class Message < ActiveRecord::Base
  as_enum :status, { :unread => 0, :read => 1, :archived => 99}, :slim => :class
end

msg = Message.new :body => 'Hello World!', status_cd => 0
msg.read?                      # => false; shortuct methods on instance are still enabled
msg.status                     # => :unread
Message.unread                 # => throws NoMethodError: undefined method `unread`
Message.statuses.unread        # => 0
Message.statuses.unread(true)  # => :unread

As a default an ArgumentError is raised if the user tries to set the field to an invalid enumeration value, to change this behaviour use the :whiny option:
```
class User < ActiveRecord::Base
  as_enum :gender, [:male, :female], :whiny => false
end
```
To define any option globally, like setting :whiny to false, or globally enable :prefix; all default options are stored in SimpleEnum.default_options, this hash can be easily changed in your initializers or wherever:
```
# e.g. setting :prefix => true (globally)
SimpleEnum.default_options[:prefix] = true
```

Best practices

Searching for certain values by using the finder methods:

User.find :all, :conditions => { :gender_cd => User.female }

Working with database backed values, now assuming that there exists a genders table:

class Person < ActiveRecord::Base
  as_enum :gender, Gender.find(:all).map { |g| [g.name.to_sym, g.id] } # map to array of symbols
end

Working with object backed values, the only requirement to enable this is that a) either a field name name exists or b) a custom method to convert an object to a symbolized form named to_enum_sym (for general uses overriding to_enum is perfectly fine) exists:

class Status < ActiveRecord::Base
  # this has a column named :name
  STATUSES = self.find(:all, :order => :name)
end

class BankTransaction < ActiveRecord::Base
  as_enum :status, Status.STATUSES
end

# what happens now? the id's of Status now serve as enumeration key and the
# Status object as the value so...    
t = BankTransaction.new
t.pending!
t.status # => #<Status id: 1, name: "pending">

# and it's also possible to access the objects/values using:
BankTransaction.statuses(:pending) # => 1, access by symbol (not) the object!
BankTransaction.statuses.pending   # => 1
BankTransaction.statuses.pending(true) # => #<Status id: 1, name: "pending">

Known issues/Open items

Maybe the :whiny option should default to false, so that generally no exceptions are thrown if a user fakes a request?
Remove the values_for_... method sometimes, it’s already deprecated anyway (in favor of Klass.<pluralized enum name>)
Clean-up code and tests -> bring down LOC ;) (but maintain Code LOC vs. Test LOC ratio which is currently 1:2.9)

SimpleEnum - unobtrusive enum-like fields for ActiveRecord

Quick start

Wait, there’s more!

Best practices

Known issues/Open items

Licence & Copyright