Active Support 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).

Namespace

Class

Methods

Constants

ALLOWED_ENCODINGS_FOR_TRANSLITERATE = [Encoding::UTF_8, Encoding::US_ASCII, Encoding::GB18030].freeze

Instance Public methods

camelize(term, uppercase_first_letter = true)

Converts strings to UpperCamelCase. If the uppercase_first_letter parameter is set to false, then produces lowerCamelCase.

Also converts ‘/’ to ‘::’ which is useful for converting paths to namespaces.

camelize('active_model')                # => "ActiveModel"
camelize('active_model', false)         # => "activeModel"
camelize('active_model/errors')         # => "ActiveModel::Errors"
camelize('active_model/errors', false)  # => "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:

camelize(underscore('SSLError'))        # => "SslError"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 70
    def camelize(term, uppercase_first_letter = true)
      string = term.to_s
      # String#camelize takes a symbol (:upper or :lower), so here we also support :lower to keep the methods consistent.
      if !uppercase_first_letter || uppercase_first_letter == :lower
        string = string.sub(inflections.acronyms_camelize_regex) { |match| match.downcase! || match }
      elsif string.match?(/\A[a-z\d]*\z/)
        return inflections.acronyms[string]&.dup || string.capitalize
      else
        string = string.sub(/^[a-z\d]*/) { |match| inflections.acronyms[match] || match.capitalize! || match }
      end
      string.gsub!(/(?:_|(\/))([a-z\d]*)/i) do
        word = $2
        substituted = inflections.acronyms[word] || word.capitalize! || word
        $1 ? "::#{substituted}" : substituted
      end
      string
    end
🔎 See on GitHub

classify(table_name)

Creates 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.)

classify('ham_and_eggs') # => "HamAndEgg"
classify('posts')        # => "Post"

Singular names are not handled correctly:

classify('calculus')     # => "Calculu"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 218
    def classify(table_name)
      # strip out any leading schema name
      camelize(singularize(table_name.to_s.sub(/.*\./, "")))
    end
🔎 See on GitHub

constantize(camel_cased_word)

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

constantize('Module')   # => Module
constantize('Foo::Bar') # => Foo::Bar

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'
  constantize('C') # => 'outside', same as ::C
end

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

📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 289
    def constantize(camel_cased_word)
      Object.const_get(camel_cased_word)
    end
🔎 See on GitHub

dasherize(underscored_word)

Replaces underscores with dashes in the string.

dasherize('puni_puni') # => "puni-puni"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 226
    def dasherize(underscored_word)
      underscored_word.tr("_", "-")
    end
🔎 See on GitHub

deconstantize(path)

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

deconstantize('Net::HTTP')   # => "Net"
deconstantize('::Net::HTTP') # => "::Net"
deconstantize('String')      # => ""
deconstantize('::String')    # => ""
deconstantize('')            # => ""

See also demodulize.

📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 256
    def deconstantize(path)
      path.to_s[0, path.rindex("::") || 0] # implementation based on the one in facets' Module#spacename
    end
🔎 See on GitHub

demodulize(path)

Removes the module part from the expression in the string.

demodulize('ActiveSupport::Inflector::Inflections') # => "Inflections"
demodulize('Inflections')                           # => "Inflections"
demodulize('::Inflections')                         # => "Inflections"
demodulize('')                                      # => ""

See also deconstantize.

📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 238
    def demodulize(path)
      path = path.to_s
      if i = path.rindex("::")
        path[(i + 2), path.length]
      else
        path
      end
    end
🔎 See on GitHub

downcase_first(string)

Converts the first character in the string to lowercase.

downcase_first('If they enjoyed The Matrix') # => "if they enjoyed The Matrix"
downcase_first('I')                          # => "i"
downcase_first('')                           # => ""
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 175
    def downcase_first(string)
      string.length > 0 ? string[0].downcase.concat(string[1..-1]) : +""
    end
🔎 See on GitHub

foreign_key(class_name, separate_class_name_and_id_with_underscore = true)

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’.

foreign_key('Message')        # => "message_id"
foreign_key('Message', false) # => "messageid"
foreign_key('Admin::Post')    # => "post_id"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 267
    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
🔎 See on GitHub

humanize(lower_case_and_underscored_word, capitalize: true, keep_id_suffix: false)

Tweaks an attribute name for display to end users.

Specifically, performs these transformations:

  • Applies human inflection rules to the argument.

  • Deletes leading underscores, if any.

  • Removes an “_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).

The trailing ‘_id’ can be kept and capitalized by setting the optional parameter keep_id_suffix to true (default is false).

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

If “SSL” was defined to be an acronym:

humanize('ssl_error') # => "SSL error"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 135
    def humanize(lower_case_and_underscored_word, capitalize: true, keep_id_suffix: false)
      result = lower_case_and_underscored_word.to_s.dup

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

      result.tr!("_", " ")
      result.lstrip!
      if !keep_id_suffix && lower_case_and_underscored_word&.end_with?("_id")
        result.delete_suffix!(" id")
      end

      result.gsub!(/([a-z\d]+)/i) do |match|
        match.downcase!
        inflections.acronyms[match] || match
      end

      if capitalize
        result.sub!(/\A\w/) do |match|
          match.upcase!
          match
        end
      end

      result
    end
🔎 See on GitHub

inflections(locale = :en)

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
📝 Source code
# File activesupport/lib/active_support/inflector/inflections.rb, line 265
    def inflections(locale = :en)
      if block_given?
        yield Inflections.instance(locale)
      else
        Inflections.instance_or_fallback(locale)
      end
    end
🔎 See on GitHub

ordinal(number)

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"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 334
    def ordinal(number)
      I18n.translate("number.nth.ordinals", number: number)
    end
🔎 See on GitHub

ordinalize(number)

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"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 347
    def ordinalize(number)
      I18n.translate("number.nth.ordinalized", number: number)
    end
🔎 See on GitHub

parameterize(string, separator: "-", preserve_case: false, locale: nil)

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

parameterize("Donald E. Knuth") # => "donald-e-knuth"
parameterize("^très|Jolie-- ")  # => "tres-jolie"

To use a custom separator, override the separator argument.

parameterize("Donald E. Knuth", separator: '_') # => "donald_e_knuth"
parameterize("^très|Jolie__ ", separator: '_')  # => "tres_jolie"

To preserve the case of the characters in a string, use the preserve_case argument.

parameterize("Donald E. Knuth", preserve_case: true) # => "Donald-E-Knuth"
parameterize("^très|Jolie-- ", preserve_case: true) # => "tres-Jolie"

It preserves dashes and underscores unless they are used as separators:

parameterize("^très|Jolie__ ")                 # => "tres-jolie__"
parameterize("^très|Jolie-- ", separator: "_") # => "tres_jolie--"
parameterize("^très_Jolie-- ", separator: ".") # => "tres_jolie--"

If the optional parameter locale is specified, the word will be parameterized as a word of that language. By default, this parameter is set to nil and it will use the configured I18n.locale.

📝 Source code
# File activesupport/lib/active_support/inflector/transliterate.rb, line 123
    def parameterize(string, separator: "-", preserve_case: false, locale: nil)
      # Replace accented chars with their ASCII equivalents.
      parameterized_string = transliterate(string, locale: locale)

      # Turn unwanted chars into the separator.
      parameterized_string.gsub!(/[^a-z0-9\-_]+/i, separator)

      unless separator.nil? || separator.empty?
        if separator == "-"
          re_duplicate_separator        = /-{2,}/
          re_leading_trailing_separator = /^-|-$/i
        else
          re_sep = Regexp.escape(separator)
          re_duplicate_separator        = /#{re_sep}{2,}/
          re_leading_trailing_separator = /^#{re_sep}|#{re_sep}$/i
        end
        # No more than one of the separator in a row.
        parameterized_string.gsub!(re_duplicate_separator, separator)
        # Remove leading/trailing separator.
        parameterized_string.gsub!(re_leading_trailing_separator, "")
      end

      parameterized_string.downcase! unless preserve_case
      parameterized_string
    end
🔎 See on GitHub

pluralize(word, locale = :en)

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.

pluralize('post')             # => "posts"
pluralize('octopus')          # => "octopi"
pluralize('sheep')            # => "sheep"
pluralize('words')            # => "words"
pluralize('CamelOctopus')     # => "CamelOctopi"
pluralize('ley', :es)         # => "leyes"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 33
    def pluralize(word, locale = :en)
      apply_inflections(word, inflections(locale).plurals, locale)
    end
🔎 See on GitHub

safe_constantize(camel_cased_word)

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

safe_constantize('Module')   # => Module
safe_constantize('Foo::Bar') # => Foo::Bar

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'
  safe_constantize('C') # => 'outside', same as ::C
end

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

safe_constantize('blargle')                  # => nil
safe_constantize('UnknownModule')            # => nil
safe_constantize('UnknownModule::Foo::Bar')  # => nil
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 315
    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 LoadError => e
      message = e.respond_to?(:original_message) ? e.original_message : e.message
      raise unless /Unable to autoload constant #{const_regexp(camel_cased_word)}/.match?(message)
    end
🔎 See on GitHub

singularize(word, locale = :en)

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.

singularize('posts')            # => "post"
singularize('octopi')           # => "octopus"
singularize('sheep')            # => "sheep"
singularize('word')             # => "word"
singularize('CamelOctopi')      # => "CamelOctopus"
singularize('leyes', :es)       # => "ley"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 50
    def singularize(word, locale = :en)
      apply_inflections(word, inflections(locale).singulars, locale)
    end
🔎 See on GitHub

tableize(class_name)

Creates 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.

tableize('RawScaledScorer') # => "raw_scaled_scorers"
tableize('ham_and_egg')     # => "ham_and_eggs"
tableize('fancyCategory')   # => "fancy_categories"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 204
    def tableize(class_name)
      pluralize(underscore(class_name))
    end
🔎 See on GitHub

titleize(word, keep_id_suffix: false)

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.

The trailing ‘_id’,‘Id’.. can be kept and capitalized by setting the optional parameter keep_id_suffix to true. By default, this parameter is false.

titleize('man from the boondocks')                       # => "Man From The Boondocks"
titleize('x-men: the last stand')                        # => "X Men: The Last Stand"
titleize('TheManWithoutAPast')                           # => "The Man Without A Past"
titleize('raiders_of_the_lost_ark')                      # => "Raiders Of The Lost Ark"
titleize('string_ending_with_id', keep_id_suffix: true)  # => "String Ending With Id"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 192
    def titleize(word, keep_id_suffix: false)
      humanize(underscore(word), keep_id_suffix: keep_id_suffix).gsub(/\b(?<!\w['’`()])[a-z]/) do |match|
        match.capitalize
      end
    end
🔎 See on GitHub

transliterate(string, replacement = "?", locale: nil)

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:

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

transliterate('Jürgen', locale: :de)
# => "Juergen"

Transliteration is restricted to UTF-8, US-ASCII, and GB18030 strings. Other encodings will raise an ArgumentError.

📝 Source code
# File activesupport/lib/active_support/inflector/transliterate.rb, line 64
    def transliterate(string, replacement = "?", locale: nil)
      raise ArgumentError, "Can only transliterate strings. Received #{string.class.name}" unless string.is_a?(String)
      raise ArgumentError, "Cannot transliterate strings with #{string.encoding} encoding" unless ALLOWED_ENCODINGS_FOR_TRANSLITERATE.include?(string.encoding)

      return string.dup if string.ascii_only?
      string = string.dup if string.frozen?

      input_encoding = string.encoding

      # US-ASCII is a subset of UTF-8 so we'll force encoding as UTF-8 if
      # US-ASCII is given. This way we can let tidy_bytes handle the string
      # in the same way as we do for UTF-8
      string.force_encoding(Encoding::UTF_8) if string.encoding == Encoding::US_ASCII

      # GB18030 is Unicode compatible but is not a direct mapping so needs to be
      # transcoded. Using invalid/undef :replace will result in loss of data in
      # the event of invalid characters, but since tidy_bytes will replace
      # invalid/undef with a "?" we're safe to do the same beforehand
      string.encode!(Encoding::UTF_8, invalid: :replace, undef: :replace) if string.encoding == Encoding::GB18030

      transliterated = I18n.transliterate(
        ActiveSupport::Multibyte::Unicode.tidy_bytes(string).unicode_normalize(:nfc),
        replacement: replacement,
        locale: locale
      )

      # Restore the string encoding of the input if it was not UTF-8.
      # Apply invalid/undef :replace as tidy_bytes does
      transliterated.encode!(input_encoding, invalid: :replace, undef: :replace) if input_encoding != transliterated.encoding

      transliterated
    end
🔎 See on GitHub

underscore(camel_cased_word)

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

Changes ‘::’ to ‘/’ to convert namespaces to paths.

underscore('ActiveModel')         # => "active_model"
underscore('ActiveModel::Errors') # => "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:

camelize(underscore('SSLError'))  # => "SslError"
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 99
    def underscore(camel_cased_word)
      return camel_cased_word.to_s.dup unless /[A-Z-]|::/.match?(camel_cased_word)
      word = camel_cased_word.to_s.gsub("::", "/")
      word.gsub!(inflections.acronyms_underscore_regex) { "#{$1 && '_' }#{$2.downcase}" }
      word.gsub!(/(?<=[A-Z])(?=[A-Z][a-z])|(?<=[a-z\d])(?=[A-Z])/, "_")
      word.tr!("-", "_")
      word.downcase!
      word
    end
🔎 See on GitHub

upcase_first(string)

Converts the first character in the string to uppercase.

upcase_first('what a Lovely Day') # => "What a Lovely Day"
upcase_first('w')                 # => "W"
upcase_first('')                  # => ""
📝 Source code
# File activesupport/lib/active_support/inflector/methods.rb, line 166
    def upcase_first(string)
      string.length > 0 ? string[0].upcase.concat(string[1..-1]) : +""
    end
🔎 See on GitHub