Field Definition

Untyped Fields

Not specifying a type for a field is the same as specifying the Object type. Such fields are untyped:

class Product
  include Mongoid::Document
  field :properties
  # Equivalent to:
  field :properties, type: Object
end

An untyped field can store values of any type which is directly serializable to BSON. This is useful when a field may contain values of different types (i.e. it is a variant type field), or when the type of values is not known ahead of time:

product = Product.new(properties: "color=white,size=large")
product.properties
# => "color=white,size=large"
product = Product.new(properties: {color: "white", size: "large"})
product.properties
# => {:color=>"white", :size=>"large"}

When values are assigned to the field, Mongoid still performs mongoization but uses the class of the value rather than the field type for mongoization logic.

product = Product.new(properties: 0..10)
product.properties
# The range 0..10, mongoized:
# => {"min"=>0, "max"=>10}

When reading data from the database, Mongoid does not perform any type conversions on untyped fields. For this reason, even though it is possible to write any BSON-serializable value into an untyped fields, values which require special handling on the database reading side will generally not work correctly in an untyped field. Among field types supported by Mongoid, values of the following types should not be stored in untyped fields:

• Date (values will be returned as Time)

• DateTime (values will be returned as Time)

• Range (values will be returned as Hash)

Field Type: StringifiedSymbol

The StringifiedSymbol field type is the recommended field type for storing values that should be exposed as symbols to Ruby applications. When using the Symbol field type, Mongoid defaults to storing values as BSON symbols. For more information on the BSON symbol type, see here. However, the BSON symbol type is deprecated and is difficult to work with in programming languages without native symbol types, so the StringifiedSymbol type allows the use of symbols while ensuring interoperability with other drivers. The StringifiedSymbol type stores all data on the database as strings, while exposing values to the application as symbols.

An example usage is shown below:

class Post
  include Mongoid::Document
  field :status, type: StringifiedSymbol
end
post = Post.new(status: :hello)
# status is stored as "hello" on the database, but returned as a Symbol
post.status
# => :hello
# String values can be assigned also:
post = Post.new(status: "hello")
# status is stored as "hello" on the database, but returned as a Symbol
post.status
# => :hello

All non-string values will be stringified upon being sent to the database (via to_s), and all values will be converted to symbols when returned to the application. Values that cannot be converted directly to symbols, such as integers and arrays, will first be converted to strings and then symbols before being returned to the application.

For example, setting an integer as status:

post = Post.new(status: 42)
post.status
# => :"42"

If the StringifiedSymbol type is applied to a field that contains BSON symbols, the values will be stored as strings instead of BSON symbols on the next save. This permits transparent lazy migration from fields that currently store either strings or BSON symbols in the database to the StringifiedSymbol field type.

Field Type: Symbol

New applications should use the StringifiedSymbol field type to store Ruby symbols in the database. The StringifiedSymbol field type provides maximum compatibility with other applications and programming languages and has the same behavior in all circumstances.

Mongoid also provides the deprecated Symbol field type for serializing Ruby symbols to BSON symbols. Because the BSON specification deprecated the BSON symbol type, the bson gem will serialize Ruby symbols into BSON strings when used on its own. However, in order to maintain backwards compatibility with older datasets, the mongo gem overrides this behavior to serialize Ruby symbols as BSON symbols. This is necessary to be able to specify queries for documents which contain BSON symbols as fields.

To override the default behavior and configure the mongo gem (and thereby Mongoid as well) to encode symbol values as strings, include the following code snippet in your project:

class Symbol
  def bson_type
    BSON::String::BSON_TYPE
  end
end

Field Type: Hash

When using a field of type Hash, be wary of adhering to the legal key names for mongoDB, or else the values will not store properly.

class Person
  include Mongoid::Document
  field :first_name
  field :url, type: Hash
  # will update the fields properly and save the values
  def set_vals
    self.first_name = 'Daniel'
    self.url = {'home_page' => 'http://www.homepage.com'}
    save
  end
  # all data will fail to save due to the illegal hash key
  def set_vals_fail
    self.first_name = 'Daniel'
    self.url = {'home.page' => 'http://www.homepage.com'}
    save
  end
end

Field Type: Time

Time fields store values as Time instances in the configured time zone.

Date and DateTime instances are converted to Time instances upon assignment to a Time field:

class Voter
  include Mongoid::Document
  field :registered_at, type: Time
end
Voter.new(registered_at: Date.today)
# => #<Voter _id: 5fdd80392c97a618f07ba344, registered_at: 2020-12-18 05:00:00 UTC>

In the above example, the value was interpreted as the beginning of today in local time, because the application was not configured to use UTC times.

Field Type: Date

Mongoid allows assignment of values of several types to Date fields:

• Date - the provided date is stored as is.

• Time, DateTime, ActiveSupport::TimeWithZone - the date component of the value is taken in the value's time zone.

• String - the date specified in the string is used.

• Integer, Float - the value is taken to be a UTC timestamp which is converted to the configured time zone (note that Mongoid.use_utc has no effect on this conversion), then the date is taken from the resulting time.

In other words, if a date is specified in the value, that date is used without first converting the value to the configured time zone.

As a date & time to date conversion is lossy (it discards the time component), especially if an application operates with times in different time zones it is recommended to explicitly convert String, Time and DateTime objects to Date objects before assigning the values to fields of type Date.

Field Type: DateTime

MongoDB stores all times as UTC timestamps. When assigning a value to a DateTime field, or when querying a DateTime field, Mongoid converts the passed in value to a UTC Time before sending it to the MongoDB server.

Time, ActiveSupport::TimeWithZone and DateTime objects embed time zone information, and the value persisted is the specified moment in time, in UTC. When the value is retrieved, the time zone in which it is returned is defined by the configured time zone settings.

class Ticket
  include Mongoid::Document
  field :opened_at, type: DateTime
end
Time.zone = 'Berlin'
ticket = Ticket.create!(opened_at: '2018-02-18 07:00:08 -0500')
 ticket.opened_at
 # => Sun, 18 Feb 2018 13:00:08 +0100
 ticket
 # => #<Ticket _id: 5c13d4b9026d7c4e7870bb2f, opened_at: 2018-02-18 12:00:08 UTC>
 Time.zone = 'America/New_York'
 ticket.opened_at
 # => Sun, 18 Feb 2018 07:00:08 -0500
 Mongoid.use_utc = true
 ticket.opened_at
 # => Sun, 18 Feb 2018 12:00:08 +0000

Mongoid also supports casting integers and floats to DateTime. When doing so, the integers/floats are assumed to be Unix timestamps (in UTC):

ticket.opened_at = 1544803974
ticket.opened_at
# => Fri, 14 Dec 2018 16:12:54 +0000

If a string is used as a DateTime field value, the behavior depends on whether the string includes a time zone. If no time zone is specified, the default Mongoid time zone is used:

Time.zone = 'America/New_York'
ticket.opened_at = 'Mar 4, 2018 10:00:00'
ticket.opened_at
# => Sun, 04 Mar 2018 15:00:00 +0000

If a time zone is specified, it is respected:

ticket.opened_at = 'Mar 4, 2018 10:00:00 +01:00'
ticket.opened_at
# => Sun, 04 Mar 2018 09:00:00 +0000

Field Type: Regexp

MongoDB supports storing regular expressions in documents, and querying using regular expressions. Note that MongoDB uses Perl-compatible regular expressions (PCRE) and Ruby uses Onigmo, which is a fork of Oniguruma regular expression engine. The two regular expression implementations generally provide equivalent functionality but have several important syntax differences.

When a field is declared to be of type Regexp, Mongoid converts Ruby regular expressions to BSON regular expressions and stores the result in MongoDB. Retrieving the field from the database produces a BSON::Regexp::Raw instance:

class Token
  include Mongoid::Document
  field :pattern, type: Regexp
end
token = Token.create!(pattern: /hello.world/m)
token.pattern
# => /hello.world/m
token.reload
token.pattern
# => #<BSON::Regexp::Raw:0x0000555f505e4a20 @pattern="hello.world", @options="ms">

Use #compile method on BSON::Regexp::Raw to get back the Ruby regular expression:

token.pattern.compile
# => /hello.world/m

Note that, if the regular expression was not originally a Ruby one, calling #compile on it may produce a different regular expression. For example, the following is a PCRE matching a string that ends in "hello":

BSON::Regexp::Raw.new('hello$', 's')
# => #<BSON::Regexp::Raw:0x0000555f51441640 @pattern="hello$", @options="s">

Compiling this regular expression produces a Ruby regular expression that matches strings containing "hello" before a newline, besides strings ending in "hello":

BSON::Regexp::Raw.new('hello$', 's').compile =~ "hello\nworld"
# => 0

This is because the meaning of $ is different between PCRE and Ruby regular expressions.

BigDecimal Fields

The BigDecimal field type is used to store numbers with increased precision.

The BigDecimal field type stores its values in two different ways in the database, depending on the value of the Mongoid.map_big_decimal_to_decimal128 global config option. If this flag is set to false (which is the default), the BigDecimal field will be stored as a string, otherwise it will be stored as a BSON::Decimal128.

The BigDecimal field type has some limitations when converting to and from a BSON::Decimal128:

• BSON::Decimal128 has a limited range and precision, while BigDecimal has no restrictions in terms of range and precision. BSON::Decimal128 has a max value of approximately 10^6145 and a min value of approximately -10^6145, and has a maximum of 34 bits of precision. When attempting to store values that don't fit into a BSON::Decimal128, it is recommended to have them stored as a string instead of a BSON::Decimal128. You can do that by setting Mongoid.map_big_decimal_to_decimal128 to false. If a value that does not fit in a BSON::Decimal128 is attempted to be stored as one, an error will be raised.

• BSON::Decimal128 is able to accept signed NaN values, while BigDecimal is not. When retrieving signed NaN values from the database using the BigDecimal field type, the NaN will be unsigned.

• BSON::Decimal128 maintains trailing zeroes when stored in the database. BigDecimal, however, does not maintain trailing zeroes, and therefore retrieving BSON::Decimal128 values using the BigDecimal field type may result in a loss of precision.

There is an additional caveat when storing a BigDecimal in a field with no type (i.e. a dynamically typed field) and Mongoid.map_big_decimal_to_decimal128 is false. In this case, the BigDecimal is stored as a string, and since a dynamic field is being used, querying for that field with a BigDecimal will not find the string for that BigDecimal, since the query is looking for a BigDecimal. In order to query for that string, the BigDecimal must first be converted to a string with to_s. Note that this is not a problem when the field has type BigDecimal.

If you wish to avoid using BigDecimal altogether, you can set the field type to BSON::Decimal128. This will allow you to keep track of trailing zeroes and signed NaN values.

Using Symbols Or Strings Instead Of Classes

Mongoid permits using symbols or strings instead of classes to specify the type of fields, for example:

class Order
  include Mongoid::Document
  field :state, type: :integer
  # Equivalent to:
  field :state, type: "integer"
  # Equivalent to:
  field :state, type: Integer
end

Only standard field types as listed below can be specified using symbols or strings in this manner. Mongoid recognizes the following expansions:

• :array => Array

• :big_decimal => BigDecimal

• :binary => BSON::Binary

• :boolean => Mongoid::Boolean

• :date => Date

• :date_time => DateTime

• :float => Float

• :hash => Hash

• :integer => Integer

• :object_id => BSON::ObjectId

• :range => Range

• :regexp => Regexp

• :set => Set

• :string => String

• :stringified_symbol => StringifiedSymbol

• :symbol => Symbol

• :time => Time

Specifying Field Default Values

A field can be configured to have a default value. The default value can be fixed, as in the following example:

class Order
  include Mongoid::Document
  field :state, type: String, default: 'created'
end

The default value can also be specified as a Proc:

class Order
  include Mongoid::Document
  field :fulfill_by, type: Time, default: ->{ Time.now + 3.days }
end

field :submitted_at, type: Time, default: Time.now
field :submitted_at, type: Time, default: ->{ Time.now }

To set a default which depends on the document's state, use self inside the Proc instance which would evaluate to the document instance being operated on:

field :fulfill_by, type: Time, default: ->{
  # Order should be fulfilled in 2 business hours.
  if (7..8).include?(self.submitted_at.hour)
    self.submitted_at + 4.hours
  elsif (9..3).include?(self.submitted_at.hour)
    self.submitted_at + 2.hours
  else
    (self.submitted_at + 1.day).change(hour: 11)
  end
}

When defining a default value as a Proc, Mongoid will apply the default after all other attributes are set and associations are initialized. To have the default be applied before the other attributes are set, use the pre_processed: true field option:

field :fulfill_by, type: Time, default: ->{ Time.now + 3.days },
  pre_processed: true

The pre_processed: true option is also necessary when specifying a custom default value via a Proc for the _id field, to ensure the _id is set correctly via associations:

field :_id, type: String, default: -> { 'hello' }, pre_processed: true

Specifying Storage Field Names

One of the drawbacks of having a schemaless database is that MongoDB must store all field information along with every document, meaning that it takes up a lot of storage space in RAM and on disk. A common pattern to limit this is to alias fields to a small number of characters, while keeping the domain in the application expressive. Mongoid allows you to do this and reference the fields in the domain via their long names in getters, setters, and criteria while performing the conversion for you.

class Band
  include Mongoid::Document
  field :n, as: :name, type: String
end
band = Band.new(name: "Placebo")
band.attributes # { "n" => "Placebo" }
criteria = Band.where(name: "Placebo")
criteria.selector # { "n" => "Placebo" }

Field Aliases

It is possible to define field aliases. The value will be stored in the destination field but can be accessed from either the destination field or from the aliased field:

class Band
  include Mongoid::Document
  field :name, type: String
  alias_attribute :n, :name
end
band = Band.new(n: 'Astral Projection')
# => #<Band _id: 5fc1c1ee2c97a64accbeb5e1, name: "Astral Projection">
band.attributes
# => {"_id"=>BSON::ObjectId('5fc1c1ee2c97a64accbeb5e1'), "name"=>"Astral Projection"}
band.n
# => "Astral Projection"

Aliases can be removed from model classes using the unalias_attribute method.

class Band
  unalias_attribute :n
end

class Band
  include Mongoid::Document
  unalias_attribute :id
  field :id, type: String
end
Band.new(id: '42')
# => #<Band _id: 5fc1c3f42c97a6590684046c, id: "42">

Reserved Names

Attempting to define a field on a document that conflicts with a reserved method name in Mongoid will raise an error. The list of reserved names can be obtained by invoking the Mongoid.destructive_fields method.

Field Redefinition

By default Mongoid allows redefining fields on a model. To raise an error when a field is redefined, set the duplicate_fields_exception configuration option to true.

With the option set to true, the following example will raise an error:

class Person
  include Mongoid::Document
  field :name
  field :name, type: String
end

To define the field anyway, use the overwrite: true option:

class Person
  include Mongoid::Document
  field :name
  field :name, type: String, overwrite: true
end

Custom IDs

By default, Mongoid defines the _id field on documents to contain a BSON::ObjectId value which is automatically generated by Mongoid.

It is possible to replace the _id field definition to change the type of the _id values or have different default values:

class Band
  include Mongoid::Document
  field :name, type: String
  field :_id, type: String, default: ->{ name }
end

It is possible to omit the default entirely:

class Band
  include Mongoid::Document
  field :_id, type: String
end

If the default on _id is omitted, and no _id value is provided by your application, Mongoid will persist the document without the _id value. In this case, if the document is a top-level document, an _id value will be assigned by the server; if the document is an embedded document, no _id value will be assigned. Mongoid will not automatically retrieve this value, if assigned, when the document is persisted - you must obtain the persisted value (and the complete persisted document) using other means:

band = Band.create!
=> #<Band _id: , >
band.id
=> nil
band.reload
# raises Mongoid::Errors::DocumentNotFound
Band.last
=> #<Band _id: 5fc681c22c97a6791f324b99, >

Omitting _id fields is more common in embedded documents.

Mongoid also defines the id field aliased to _id. The id alias can be removed if desired (such as to integrate with systems that use the id field to store value different from _id.

Uncastable Values

In Mongoid 8, Mongoid has standardized the treatment of the assignment and reading of "uncastable" values. A value is considered "uncastable" when it cannot be coerced to the type of its field. For example, an array would be an "uncastable" value to an Integer field.

class User
  include Mongoid::Document
  field :name, type: Integer
end
User.new(name: [ "hello" ])

user = User.new(name: [ "Mike", "Trout" ])
# => #<User _id: 62b222d43282a47bf73e3264, name: nil>

user.attributes_before_type_cast["name"]
# => ["Mike", "Trout"]

class User
  include Mongoid::Document
  field :name, type: Integer
end

{ _id: ..., name: [ "Mike", "Trout" ] }

User.first.name
# => nil

user.attributes_before_type_cast["name"]
# => ["Mike", "Trout"]

Custom Getters And Setters

You may override getters and setters for fields to modify the values when they are being accessed or written. The getters and setters use the same name as the field. Use read_attribute and write_attribute methods inside the getters and setters to operate on the raw attribute values.

For example, Mongoid provides the :default field option to write a default value into the field. If you wish to have a field default value in your application but do not wish to persist it, you can override the getter as follows:

class DistanceMeasurement
  include Mongoid::Document
  field :value, type: Float
  field :unit, type: String
  def unit
    read_attribute(:unit) || "m"
  end
  def to_s
    "#{value} #{unit}"
  end
end
measurement = DistanceMeasurement.new(value: 2)
measurement.to_s
# => "2.0 m"
measurement.attributes
# => {"_id"=>BSON::ObjectId('613fa0b0a15d5d61502f3447'), "value"=>2.0}

To give another example, a field which converts empty strings to nil values may be implemented as follows:

class DistanceMeasurement
  include Mongoid::Document
  field :value, type: Float
  field :unit, type: String
  def unit=(value)
    if value.blank?
      value = nil
    end
    write_attribute(:unit, value)
  end
end
measurement = DistanceMeasurement.new(value: 2, unit: "")
measurement.attributes
# => {"_id"=>BSON::ObjectId('613fa15aa15d5d617216104c'), "value"=>2.0, "unit"=>nil}

Custom Field Types

You can define custom types in Mongoid and determine how they are serialized and deserialized. In this example, we define a new field type Point, which we can use in our model class as follows:

class Profile
  include Mongoid::Document
  field :location, type: Point
end

Then make a Ruby class to represent the type. This class must define methods used for MongoDB serialization and deserialization as follows:

class Point
  attr_reader :x, :y
  def initialize(x, y)
    @x, @y = x, y
  end
  # Converts an object of this instance into a database friendly value.
  # In this example, we store the values in the database as array.
  def mongoize
    [ x, y ]
  end
  class << self
    # Takes any possible object and converts it to how it would be
    # stored in the database.
    def mongoize(object)
      case object
      when Point then object.mongoize
      when Hash then Point.new(object[:x], object[:y]).mongoize
      else object
      end
    end
    # Get the object as it was stored in the database, and instantiate
    # this custom class from it.
    def demongoize(object)
      Point.new(object[0], object[1])
    end
    # Converts the object that was supplied to a criteria and converts it
    # into a query-friendly form.
    def evolve(object)
      case object
      when Point then object.mongoize
      else object
      end
    end
  end
end

The instance method mongoize takes an instance of your custom type object, and converts it into a representation of how it will be stored in the database, i.e. to pass to the MongoDB Ruby driver. In our example above, we want to store our Point object as an Array in the form [ x, y ].

The class method mongoize is similar to the instance method, however it must handle objects of all possible types as inputs. The mongoize method is used when calling the setter methods for fields of your custom type.

point = Point.new(12, 24)
venue = Venue.new(location: point) # This uses the Point#mongoize instance method.
venue = Venue.new(location: [ 12, 24 ]) # This uses the Point.mongoize class method.

The class method demongoize does the inverse of mongoize. It takes the raw object from the MongoDB Ruby driver and converts it to an instance of your custom type. In this case, the database driver returns an Array and we instantiate a Point from it. The demongoize method is used when calling the getters of fields for your custom type. Note that in the example above, since demongoize calls Point.new, a new instance of Point will be generated on each call to the getter.

Mongoid will always call the demongoize method on values that were retrieved from the database, but applications may, in theory, call demongoize with arbitrary input. It is recommended that applications add handling for arbitrary input in their demongoize methods. We can rewrite Point's demongoize method as follows:

def demongoize(object)
  if object.is_a?(Array) && object.length == 2
    Point.new(object[0], object[1])
  end
end

Notice that demongoize will only create a new Point if given an array of length 2, and will return nil otherwise. Both the mongoize and demongoize methods should be prepared to receive arbitrary input and should return nil on values that are uncastable to your custom type. See the section on Uncastable Values for more details.

Lastly, the class method evolve is similar to mongoize, however it is used when transforming objects for use in Mongoid query criteria.

point = Point.new(12, 24)
Venue.where(location: point) # This uses Point.evolve

The evolve method should also be prepared to receive arbitrary input, however, unlike the mongoize and demongoize methods, it should return the inputted value on values that are uncastable to your custom type. See the section on Uncastable Values for more details.

class ColorMapping
  MAPPING = {
    'black' => 0,
    'white' => 1,
  }.freeze
  INVERSE_MAPPING = MAPPING.invert.freeze
  class << self
    # Takes application-scope value and converts it to how it would be
    # stored in the database. Converts invalid values to nil.
    def mongoize(object)
      MAPPING[object]
    end
    # Get the value as it was stored in the database, and convert to
    # application-scope value. Converts invalid values to nil.
    def demongoize(object)
      INVERSE_MAPPING[object]
    end
    # Converts the object that was supplied to a criteria and converts it
    # into a query-friendly form. Returns invalid values as is.
    def evolve(object)
      MAPPING.fetch(object, object)
    end
  end
end
class Profile
  include Mongoid::Document
  field :color, type: ColorMapping
end
profile = Profile.new(color: 'white')
profile.color
# => "white"
# Writes 0 to color field
profile.save!

Custom Field Options

You may define custom options for the field macro function which extend its behavior at the your time model classes are loaded.

As an example, we will define a :max_length option which will add a length validator for the field. First, declare the new field option in an initializer, specifying its handler function as a block:

# in /config/initializers/mongoid_custom_fields.rb
Mongoid::Fields.option :max_length do |model, field, value|
  model.validates_length_of field.name, maximum: value
end

Then, use it your model class:

class Person
  include Mongoid::Document
  field :name, type: String, max_length: 10
end

Note that the handler function will be invoked whenever the option is used in the field definition, even if the option's value is false or nil.

Special Characters in Field Names

Mongoid permits dynamic field names to include spaces and punctuation:

bob = Person.new('hello world' => 'MDB')
bob.send('hello world')
# => "MDB"
bob.write_attribute("hello%world", 'MDB')
bob[:"hello%world"]
# => "MDB"

Localize :present Field Option

Mongoid supports the :present option when creating a localized field:

class Product
  include Mongoid::Document
  field :description, localize: :present
end

This option automatically removes blank values (i.e. those that return true for the blank? method) from the _translations hash:

I18n.default_locale = :en
product = Product.new
product.description = "Marvelous!"
I18n.locale = :de
product.description = "Fantastisch!"
product.description_translations
# { "en" => "Marvelous!", "de" => "Fantastisch!" }
product.description = ""
product.description_translations
# { "en" => "Marvelous!" }

When the empty string is written for the :de locale, the "de" key is removed from the _translations hash instead of writing the empty string.

Fallbacks

Mongoid integrates with i18n fallbacks. To use the fallbacks, the respective functionality must be explicitly enabled.

In a Rails application, set the config.i18n.fallbacks configuration setting to true in your environment and specify the fallback languages:

config.i18n.fallbacks = true
config.after_initialize do
  I18n.fallbacks[:de] = [ :en, :es ]
end

In a non-Rails application, include the fallbacks module into the I18n backend you are using and specify the fallback languages:

require "i18n/backend/fallbacks"
I18n::Backend::Simple.send(:include, I18n::Backend::Fallbacks)
I18n.fallbacks[:de] = [ :en, :es ]

When fallbacks are enabled, if a translation is not present in the active language, translations will be looked up in the fallback languages:

product = Product.new
I18n.locale = :en
product.description = "Marvelous!"
I18n.locale = :de
product.description # "Marvelous!"

Mongoid also defines a :fallbacks option on fields, which can be used to disable fallback functionality on a specific field:

class Product
  include Mongoid::Document
  field :description, type: String, localize: true, fallbacks: false
end
product = Product.new
I18n.locale = :en
product.description = "Marvelous!"
I18n.locale = :de
product.description # nil

Note that this option defaults to true.

Querying

When querying for localized fields using Mongoid's criteria API, Mongoid will automatically alter the criteria to match the current locale.

# Match all products with Marvelous as the description. Locale is en.
Product.where(description: "Marvelous!")
# The resulting MongoDB query filter: { "description.en" : "Marvelous!" }

Indexing

If you plan to be querying extensively on localized fields, you should index each of the locales that you plan on searching on.

class Product
  include Mongoid::Document
  field :description, localize: true
  index "description.de" => 1
  index "description.en" => 1
end