cheat sheets.

EXAMPLE
=======
  class User
    include Mongoid::Document
    include Mongoid::Timestamps # adds automagic fields created_at, updated_at
    references_many :posts
    embeds_one :profile, :dependent => :destroy
    field :fieldname, :type => Array / BigDecimal / Boolean / Date / DateTime
                             / Float / Hash / Integer / String / Symbol / Time
    index :fieldname
  end

RELATIONS
=========
  EMBEDDING DATA IN THE SAME TABLE:

  embeds_one :profile
  embeds_many :settings
  embedded_in :user, :inverse_of => :settings

  REFERENCING DATA IN AN OTHER TABLE:

  referenced_in :user
  references_one :profile, :inverse_of => user
  references_many :photos, :inverse_of => user


PERSISTENCE
===========

  In order to make sure data is actually to be written to disk, you need to tell
  mongoid

  .safely.save

  (!Mongoid only fires the callback of the document that the persistence action
  was executed on)

QUERIES
=======

  .where(:amount.gt => 100, :active => true)
  .any_in(:category => array)
  .all_in(:category => array)
  .any_of({ :shape => "round" }, { :color => "red" })
  .and(:amount.gt => 100, :account_status => "active")
  .excludes(:status => "blocked")
  .not_in(:status => ["blocked", "unverified"])
  .only(:first_name, :last_name) # only retrieve these fields
  .limit(20)
  .skip(100)

ORDER
=====

  .desc(:last_name).asc(:first_name)
  .order_by(:last_name.desc, :first_name.asc, :city.desc)

CRITERIAS
=========

  .where(:title.all => ["Sir"])
  .where(:age.exists => true)
  .where(:age.gt => 18)
  .where(:age.gte => 18)
  .where(:title.in => ["Sir", "Madam"])
  .where(:age.lt => 55)
  .where(:age.lte => 55)
  .where(:title.ne => "Mr")
  .where(:title.nin => ["Esquire"])
  .where(:aliases.size => 2)
  .where(:location.near => [ 22.5, -21.33 ])
  .where(:location.within => { "$center" => [ [ 50, -40 ], 1 ] })

CALCULATIONS
============

  .max(:age)
  .min(:quantity)
  .sum(:total)

RAKE TASKS

  db:create
  db:create_indexes
  db:drop
  db:migrate
  db:schema:load
  db:seed
  db:setup
  db:test:prepare