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, you'll need to correct it yourself (explained below).

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Instance Public methods
camelize(term, uppercase_first_letter = true)

By default, camelizeconverts strings to UpperCamelCase. If the argument to camelizeis set to :lowerthen camelizeproduces lowerCamelCase.

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

Examples:

"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 camelizeas the inverse of underscore, though there are cases where that does not hold:

"SSLError".underscore.camelize # => "SslError"
# File activesupport/lib/active_support/inflector/methods.rb, line 55
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]*)/i) { "#{$1}#{inflections.acronyms[$2] || $2.capitalize}" }.gsub('/', '::')
end
classify(table_name)

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 classifywith constantize.)

Examples:

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

Singular names are not handled correctly:

"business".classify     # => "Busines"
# File activesupport/lib/active_support/inflector/methods.rb, line 140
def classify(table_name)
  # strip out any leading schema name
  camelize(singularize(table_name.to_s.sub(/.*\./, '')))
end
constantize(camel_cased_word)

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 activesupport/lib/active_support/inflector/methods.rb, line 213
def constantize(camel_cased_word)
  names = camel_cased_word.split('::')
  names.shift if names.empty? || names.first.empty?

  constant = Object
  names.each do |name|
    constant = constant.const_defined?(name) ? constant.const_get(name) : constant.const_missing(name)
  end
  constant
end
dasherize(underscored_word)

Replaces underscores with dashes in the string.

Example:

"puni_puni" # => "puni-puni"
# File activesupport/lib/active_support/inflector/methods.rb, line 149
def dasherize(underscored_word)
  underscored_word.gsub(/_/, '-')
end
deconstantize(path)

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 activesupport/lib/active_support/inflector/methods.rb, line 177
def deconstantize(path)
  path.to_s[0...(path.rindex('::') || 0)] # implementation based on the one in facets' Module#spacename
end
demodulize(path)

Removes the module part from the expression in the string:

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

See also deconstantize.

# File activesupport/lib/active_support/inflector/methods.rb, line 159
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)

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

Examples:

"Message".foreign_key        # => "message_id"
"Message".foreign_key(false) # => "messageid"
"Admin::Post".foreign_key    # => "post_id"
# File activesupport/lib/active_support/inflector/methods.rb, line 189
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)

Capitalizes the first word and turns underscores into spaces and strips a trailing “_id”, if any. Like titleize, this is meant for creating pretty output.

Examples:

"employee_salary" # => "Employee salary"
"author_id"       # => "Author"
# File activesupport/lib/active_support/inflector/methods.rb, line 94
def humanize(lower_case_and_underscored_word)
  result = lower_case_and_underscored_word.to_s.dup
  inflections.humans.each { |(rule, replacement)| break if result.gsub!(rule, replacement) }
  result.gsub!(/_id$/, "")
  result.gsub!(/_/, ' ')
  result.gsub(/([a-z\d]*)/i) { |match|
    "#{inflections.acronyms[match] || match.downcase}"
  }.gsub(/^\w/) { $&.upcase }
end
inflections()

Yields a singleton instance of Inflector::Inflections so you can specify additional inflector rules.

Example:

ActiveSupport::Inflector.inflections do |inflect|
  inflect.uncountable "rails"
end
# File activesupport/lib/active_support/inflector/inflections.rb, line 166
def inflections
  if block_given?
    yield Inflections.instance
  else
    Inflections.instance
  end
end
ordinalize(number)

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

Examples:

ordinalize(1)     # => "1st"
ordinalize(2)     # => "2nd"
ordinalize(1002)  # => "1002nd"
ordinalize(1003)  # => "1003rd"
ordinalize(-11)   # => "-11th"
ordinalize(-1021) # => "-1021st"
# File activesupport/lib/active_support/inflector/methods.rb, line 279
def ordinalize(number)
  if (11..13).include?(number.to_i.abs % 100)
    "#{number}th"
  else
    case number.to_i.abs % 10
      when 1; "#{number}st"
      when 2; "#{number}nd"
      when 3; "#{number}rd"
      else    "#{number}th"
    end
  end
end
parameterize(string, sep = '-')

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

Examples

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 activesupport/lib/active_support/inflector/transliterate.rb, line 81
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\-_]+/i, 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}$/i, '')
  end
  parameterized_string.downcase
end
pluralize(word)

Returns the plural form of the word in the string.

Examples:

"post".pluralize             # => "posts"
"octopus".pluralize          # => "octopi"
"sheep".pluralize            # => "sheep"
"words".pluralize            # => "words"
"CamelOctopus".pluralize     # => "CamelOctopi"
# File activesupport/lib/active_support/inflector/methods.rb, line 24
def pluralize(word)
  apply_inflections(word, inflections.plurals)
end
safe_constantize(camel_cased_word)

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 activesupport/lib/active_support/inflector/methods.rb, line 258
def safe_constantize(camel_cased_word)
  begin
    constantize(camel_cased_word)
  rescue NameError => e
    raise unless e.message =~ /(uninitialized constant|wrong constant name) #{const_regexp(camel_cased_word)}$/ ||
      e.name.to_s == camel_cased_word.to_s
  rescue ArgumentError => e
    raise unless e.message =~ /not missing constant #{const_regexp(camel_cased_word)}\!$/
  end
end
singularize(word)

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

Examples:

"posts".singularize            # => "post"
"octopi".singularize           # => "octopus"
"sheep".singularize            # => "sheep"
"word".singularize             # => "word"
"CamelOctopi".singularize      # => "CamelOctopus"
# File activesupport/lib/active_support/inflector/methods.rb, line 36
def singularize(word)
  apply_inflections(word, inflections.singulars)
end
tableize(class_name)

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

Examples

"RawScaledScorer".tableize # => "raw_scaled_scorers"
"egg_and_ham".tableize     # => "egg_and_hams"
"fancyCategory".tableize   # => "fancy_categories"
# File activesupport/lib/active_support/inflector/methods.rb, line 126
def tableize(class_name)
  pluralize(underscore(class_name))
end
titleize(word)

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

titleizeis also aliased as as titlecase.

Examples:

"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 activesupport/lib/active_support/inflector/methods.rb, line 115
def titleize(word)
  humanize(underscore(word)).gsub(/\b('?[a-z])/) { $1.capitalize }
end
transliterate(string, replacement = "?")

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.rulei18n 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.rulecan 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 => lambda {|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 activesupport/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)

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

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

Examples:

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

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

"SSLError".underscore.camelize # => "SslError"
# File activesupport/lib/active_support/inflector/methods.rb, line 77
def underscore(camel_cased_word)
  word = camel_cased_word.to_s.dup
  word.gsub!(/::/, '/')
  word.gsub!(/(?:([A-Za-z\d])|^)(#{inflections.acronym_regex})(?=\b|[^a-z])/) { "#{$1}#{$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