module ActiveSupport::Inflector

The Inflector transforms words from singular to plural, class names to table names, modularized class names to ones without, and class names to foreign keys. The default inflections for pluralization, singularization, and uncountable words are kept in inflections.rb.

The Rails core team has stated patches for the inflections library will not be accepted in order to avoid breaking legacy applications which may be relying on errant inflections. If you discover an incorrect inflection and require it for your application or wish to define rules for languages other than English, please correct or add them yourself (explained below).

Public Instance Methods

camelize(term, uppercase_first_letter = true) click to toggle source

By default, camelize converts strings to UpperCamelCase. If the argument to camelize is set to :lower then camelize produces lowerCamelCase.

camelize will also convert '/' to '::' which is useful for converting paths to namespaces.

'active_model'.camelize                # => "ActiveModel"
'active_model'.camelize(:lower)        # => "activeModel"
'active_model/errors'.camelize         # => "ActiveModel::Errors"
'active_model/errors'.camelize(:lower) # => "activeModel::Errors"

As a rule of thumb you can think of camelize as the inverse of underscore, though there are cases where that does not hold:

'SSLError'.underscore.camelize # => "SslError"
# File lib/active_support/inflector/methods.rb, line 67
def camelize(term, uppercase_first_letter = true)
  string = term.to_s
  if uppercase_first_letter
    string = string.sub(/^[a-z\d]*/) { inflections.acronyms[$&] || $&.capitalize }
  else
    string = string.sub(/^(?:#{inflections.acronym_regex}(?=\b|[A-Z_])|\w)/) { $&.downcase }
  end
  string.gsub!(/(?:_|(\/))([a-z\d]*)/) { "#{$1}#{inflections.acronyms[$2] || $2.capitalize}" }
  string.gsub!(/\//, '::')
  string
end
classify(table_name) click to toggle source

Create a class name from a plural table name like Rails does for table names to models. Note that this returns a string and not a Class (To convert to an actual class follow classify with constantize).

'egg_and_hams'.classify # => "EggAndHam"
'posts'.classify        # => "Post"

Singular names are not handled correctly:

'calculus'.classify     # => "Calculu"
# File lib/active_support/inflector/methods.rb, line 178
def classify(table_name)
  # strip out any leading schema name
  camelize(singularize(table_name.to_s.sub(/.*\./, '')))
end
constantize(camel_cased_word) click to toggle source

Tries to find a constant with the name specified in the argument string.

'Module'.constantize     # => Module
'Test::Unit'.constantize # => Test::Unit

The name is assumed to be the one of a top-level constant, no matter whether it starts with “::” or not. No lexical context is taken into account:

C = 'outside'
module M
  C = 'inside'
  C               # => 'inside'
  'C'.constantize # => 'outside', same as ::C
end

NameError is raised when the name is not in CamelCase or the constant is unknown.

# File lib/active_support/inflector/methods.rb, line 249
def constantize(camel_cased_word)
  names = camel_cased_word.split('::')

  # Trigger a built-in NameError exception including the ill-formed constant in the message.
  Object.const_get(camel_cased_word) if names.empty?

  # Remove the first blank element in case of '::ClassName' notation.
  names.shift if names.size > 1 && names.first.empty?

  names.inject(Object) do |constant, name|
    if constant == Object
      constant.const_get(name)
    else
      candidate = constant.const_get(name)
      next candidate if constant.const_defined?(name, false)
      next candidate unless Object.const_defined?(name)

      # Go down the ancestors to check if it is owned directly. The check
      # stops when we reach Object or the end of ancestors tree.
      constant = constant.ancestors.inject do |const, ancestor|
        break const    if ancestor == Object
        break ancestor if ancestor.const_defined?(name, false)
        const
      end

      # owner is in Object, so raise
      constant.const_get(name, false)
    end
  end
end
dasherize(underscored_word) click to toggle source

Replaces underscores with dashes in the string.

'puni_puni'.dasherize # => "puni-puni"
# File lib/active_support/inflector/methods.rb, line 186
def dasherize(underscored_word)
  underscored_word.tr('_', '-')
end
deconstantize(path) click to toggle source

Removes the rightmost segment from the constant expression in the string.

'Net::HTTP'.deconstantize   # => "Net"
'::Net::HTTP'.deconstantize # => "::Net"
'String'.deconstantize      # => ""
'::String'.deconstantize    # => ""
''.deconstantize            # => ""

See also demodulize.

# File lib/active_support/inflector/methods.rb, line 216
def deconstantize(path)
  path.to_s[0, path.rindex('::') || 0] # implementation based on the one in facets' Module#spacename
end
demodulize(path) click to toggle source

Removes the module part from the expression in the string.

'ActiveRecord::CoreExtensions::String::Inflections'.demodulize # => "Inflections"
'Inflections'.demodulize                                       # => "Inflections"
'::Inflections'.demodulize                                     # => "Inflections"
''.demodulize                                                  # => ""

See also deconstantize.

# File lib/active_support/inflector/methods.rb, line 198
def demodulize(path)
  path = path.to_s
  if i = path.rindex('::')
    path[(i+2)..-1]
  else
    path
  end
end
foreign_key(class_name, separate_class_name_and_id_with_underscore = true) click to toggle source

Creates a foreign key name from a class name. separate_class_name_and_id_with_underscore sets whether the method should put '_' between the name and 'id'.

'Message'.foreign_key        # => "message_id"
'Message'.foreign_key(false) # => "messageid"
'Admin::Post'.foreign_key    # => "post_id"
# File lib/active_support/inflector/methods.rb, line 227
def foreign_key(class_name, separate_class_name_and_id_with_underscore = true)
  underscore(demodulize(class_name)) + (separate_class_name_and_id_with_underscore ? "_id" : "id")
end
humanize(lower_case_and_underscored_word, options = {}) click to toggle source

Tweaks an attribute name for display to end users.

Specifically, humanize performs these transformations:

* Applies human inflection rules to the argument.
* Deletes leading underscores, if any.
* Removes a "_id" suffix if present.
* Replaces underscores with spaces, if any.
* Downcases all words except acronyms.
* Capitalizes the first word.

The capitalization of the first word can be turned off by setting the :capitalize option to false (default is true).

humanize('employee_salary')              # => "Employee salary"
humanize('author_id')                    # => "Author"
humanize('author_id', capitalize: false) # => "author"
humanize('_id')                          # => "Id"

If “SSL” was defined to be an acronym:

humanize('ssl_error') # => "SSL error"
# File lib/active_support/inflector/methods.rb, line 124
def humanize(lower_case_and_underscored_word, options = {})
  result = lower_case_and_underscored_word.to_s.dup

  inflections.humans.each { |(rule, replacement)| break if result.sub!(rule, replacement) }

  result.sub!(/\A_+/, '')
  result.sub!(/_id\z/, '')
  result.tr!('_', ' ')

  result.gsub!(/([a-z\d]*)/) do |match|
    "#{inflections.acronyms[match] || match.downcase}"
  end

  if options.fetch(:capitalize, true)
    result.sub!(/\A\w/) { |match| match.upcase }
  end

  result
end
inflections(locale = :en) { |instance| ... } click to toggle source

Yields a singleton instance of Inflector::Inflections so you can specify additional inflector rules. If passed an optional locale, rules for other languages can be specified. If not specified, defaults to :en. Only rules for English are provided.

ActiveSupport::Inflector.inflections(:en) do |inflect|
  inflect.uncountable 'rails'
end
# File lib/active_support/inflector/inflections.rb, line 203
def inflections(locale = :en)
  if block_given?
    yield Inflections.instance(locale)
  else
    Inflections.instance(locale)
  end
end
ordinal(number) click to toggle source

Returns the suffix that should be added to a number to denote the position in an ordered sequence such as 1st, 2nd, 3rd, 4th.

ordinal(1)     # => "st"
ordinal(2)     # => "nd"
ordinal(1002)  # => "nd"
ordinal(1003)  # => "rd"
ordinal(-11)   # => "th"
ordinal(-1021) # => "st"
# File lib/active_support/inflector/methods.rb, line 320
def ordinal(number)
  abs_number = number.to_i.abs

  if (11..13).include?(abs_number % 100)
    "th"
  else
    case abs_number % 10
      when 1; "st"
      when 2; "nd"
      when 3; "rd"
      else    "th"
    end
  end
end
ordinalize(number) click to toggle source

Turns a number into an ordinal string used to denote the position in an ordered sequence such as 1st, 2nd, 3rd, 4th.

ordinalize(1)     # => "1st"
ordinalize(2)     # => "2nd"
ordinalize(1002)  # => "1002nd"
ordinalize(1003)  # => "1003rd"
ordinalize(-11)   # => "-11th"
ordinalize(-1021) # => "-1021st"
# File lib/active_support/inflector/methods.rb, line 344
def ordinalize(number)
  "#{number}#{ordinal(number)}"
end
parameterize(string, sep = '-') click to toggle source

Replaces special characters in a string so that it may be used as part of a 'pretty' URL.

class Person
  def to_param
    "#{id}-#{name.parameterize}"
  end
end

@person = Person.find(1)
# => #<Person id: 1, name: "Donald E. Knuth">

<%= link_to(@person.name, person_path(@person)) %>
# => <a href="/person/1-donald-e-knuth">Donald E. Knuth</a>
# File lib/active_support/inflector/transliterate.rb, line 80
def parameterize(string, sep = '-')
  # replace accented chars with their ascii equivalents
  parameterized_string = transliterate(string)
  # Turn unwanted chars into the separator
  parameterized_string.gsub!(/[^a-z0-9\-_]+/, sep)
  unless sep.nil? || sep.empty?
    re_sep = Regexp.escape(sep)
    # No more than one of the separator in a row.
    parameterized_string.gsub!(/#{re_sep}{2,}/, sep)
    # Remove leading/trailing separator.
    parameterized_string.gsub!(/^#{re_sep}|#{re_sep}$/, '')
  end
  parameterized_string.downcase
end
pluralize(word, locale = :en) click to toggle source

Returns the plural form of the word in the string.

If passed an optional locale parameter, the word will be pluralized using rules defined for that language. By default, this parameter is set to :en.

'post'.pluralize             # => "posts"
'octopus'.pluralize          # => "octopi"
'sheep'.pluralize            # => "sheep"
'words'.pluralize            # => "words"
'CamelOctopus'.pluralize     # => "CamelOctopi"
'ley'.pluralize(:es)         # => "leyes"
# File lib/active_support/inflector/methods.rb, line 30
def pluralize(word, locale = :en)
  apply_inflections(word, inflections(locale).plurals)
end
safe_constantize(camel_cased_word) click to toggle source

Tries to find a constant with the name specified in the argument string.

'Module'.safe_constantize     # => Module
'Test::Unit'.safe_constantize # => Test::Unit

The name is assumed to be the one of a top-level constant, no matter whether it starts with “::” or not. No lexical context is taken into account:

C = 'outside'
module M
  C = 'inside'
  C                    # => 'inside'
  'C'.safe_constantize # => 'outside', same as ::C
end

nil is returned when the name is not in CamelCase or the constant (or part of it) is unknown.

'blargle'.safe_constantize  # => nil
'UnknownModule'.safe_constantize  # => nil
'UnknownModule::Foo::Bar'.safe_constantize  # => nil
# File lib/active_support/inflector/methods.rb, line 302
def safe_constantize(camel_cased_word)
  constantize(camel_cased_word)
rescue NameError => e
  raise if e.name && !(camel_cased_word.to_s.split("::").include?(e.name.to_s) ||
    e.name.to_s == camel_cased_word.to_s)
rescue ArgumentError => e
  raise unless e.message =~ /not missing constant #{const_regexp(camel_cased_word)}\!$/
end
singularize(word, locale = :en) click to toggle source

The reverse of pluralize, returns the singular form of a word in a string.

If passed an optional locale parameter, the word will be singularized using rules defined for that language. By default, this parameter is set to :en.

'posts'.singularize            # => "post"
'octopi'.singularize           # => "octopus"
'sheep'.singularize            # => "sheep"
'word'.singularize             # => "word"
'CamelOctopi'.singularize      # => "CamelOctopus"
'leyes'.singularize(:es)       # => "ley"
# File lib/active_support/inflector/methods.rb, line 47
def singularize(word, locale = :en)
  apply_inflections(word, inflections(locale).singulars)
end
tableize(class_name) click to toggle source

Create the name of a table like Rails does for models to table names. This method uses the pluralize method on the last word in the string.

'RawScaledScorer'.tableize # => "raw_scaled_scorers"
'egg_and_ham'.tableize     # => "egg_and_hams"
'fancyCategory'.tableize   # => "fancy_categories"
# File lib/active_support/inflector/methods.rb, line 164
def tableize(class_name)
  pluralize(underscore(class_name))
end
titleize(word) click to toggle source

Capitalizes all the words and replaces some characters in the string to create a nicer looking title. titleize is meant for creating pretty output. It is not used in the Rails internals.

titleize is also aliased as titlecase.

'man from the boondocks'.titleize   # => "Man From The Boondocks"
'x-men: the last stand'.titleize    # => "X Men: The Last Stand"
'TheManWithoutAPast'.titleize       # => "The Man Without A Past"
'raiders_of_the_lost_ark'.titleize  # => "Raiders Of The Lost Ark"
# File lib/active_support/inflector/methods.rb, line 154
def titleize(word)
  humanize(underscore(word)).gsub(/\b(?<!['’`])[a-z]/) { $&.capitalize }
end
transliterate(string, replacement = "?") click to toggle source

Replaces non-ASCII characters with an ASCII approximation, or if none exists, a replacement character which defaults to “?”.

transliterate('Ærøskøbing')
# => "AEroskobing"

Default approximations are provided for Western/Latin characters, e.g, “ø”, “ñ”, “é”, “ß”, etc.

This method is I18n aware, so you can set up custom approximations for a locale. This can be useful, for example, to transliterate German's “ü” and “ö” to “ue” and “oe”, or to add support for transliterating Russian to ASCII.

In order to make your custom transliterations available, you must set them as the i18n.transliterate.rule i18n key:

# Store the transliterations in locales/de.yml
i18n:
  transliterate:
    rule:
      ü: "ue"
      ö: "oe"

# Or set them using Ruby
I18n.backend.store_translations(:de, i18n: {
  transliterate: {
    rule: {
      'ü' => 'ue',
      'ö' => 'oe'
    }
  }
})

The value for i18n.transliterate.rule can be a simple Hash that maps characters to ASCII approximations as shown above, or, for more complex requirements, a Proc:

I18n.backend.store_translations(:de, i18n: {
  transliterate: {
    rule: ->(string) { MyTransliterator.transliterate(string) }
  }
})

Now you can have different transliterations for each locale:

I18n.locale = :en
transliterate('Jürgen')
# => "Jurgen"

I18n.locale = :de
transliterate('Jürgen')
# => "Juergen"
# File lib/active_support/inflector/transliterate.rb, line 60
def transliterate(string, replacement = "?")
  I18n.transliterate(ActiveSupport::Multibyte::Unicode.normalize(
    ActiveSupport::Multibyte::Unicode.tidy_bytes(string), :c),
      :replacement => replacement)
end
underscore(camel_cased_word) click to toggle source

Makes an underscored, lowercase form from the expression in the string.

Changes '::' to '/' to convert namespaces to paths.

'ActiveModel'.underscore         # => "active_model"
'ActiveModel::Errors'.underscore # => "active_model/errors"

As a rule of thumb you can think of underscore as the inverse of camelize, though there are cases where that does not hold:

'SSLError'.underscore.camelize # => "SslError"
# File lib/active_support/inflector/methods.rb, line 90
def underscore(camel_cased_word)
  return camel_cased_word unless camel_cased_word =~ /[A-Z-]|::/
  word = camel_cased_word.to_s.gsub(/::/, '/')
  word.gsub!(/(?:(?<=([A-Za-z\d]))|\b)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1 && '_'}#{$2.downcase}" }
  word.gsub!(/([A-Z\d]+)([A-Z][a-z])/,'\1_\2')
  word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
  word.tr!("-", "_")
  word.downcase!
  word
end

Private Instance Methods

apply_inflections(word, rules) click to toggle source

Applies inflection rules for singularize and pluralize.

apply_inflections('post', inflections.plurals)    # => "posts"
apply_inflections('posts', inflections.singulars) # => "post"
# File lib/active_support/inflector/methods.rb, line 371
def apply_inflections(word, rules)
  result = word.to_s.dup

  if word.empty? || inflections.uncountables.include?(result.downcase[/\b\w+\Z/])
    result
  else
    rules.each { |(rule, replacement)| break if result.sub!(rule, replacement) }
    result
  end
end