Here is my mongoid.yml:
development:
sessions:
default:
hosts:

• localhost:27017
  database: dev_project_db
  options:
  identity_map_enabled: true
  include_root_in_json: false
  raise_not_found_error: false

Console:
irb(main):015:0> user = User.find_by(email: "jhon@doe.net")
Mongoid::Errors::DocumentNotFound:
Problem:
Document not found for class Invoice with attributes {:email => "jhon@doe.net"}.
Summary:
When calling Invoice.find_by with a hash of attributes, all attributes provided must match a document in the database or this error will be raised.
Resolution:
Search for attributes that are in the database or set the Mongoid.raise_not_found_error configuration option to false, which will cause a nil to be returned instead of raising this error.
from /Users/yacobusreinhart/local/tmp/Invoice/gems/mongoid/lib/mongoid/finders.rb:106:in `find_by'
from (irb):15
from /Users/yacobusreinhart/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.2/lib/rails/commands/console.rb:47:in `start'
from /Users/yacobusreinhart/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.2/lib/rails/commands/console.rb:8:in `start'
from /Users/yacobusreinhart/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.2/lib/rails/commands.rb:41:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'

irb(main):016:0> Mongoid.raise_not_found_error
=> true

The problem occurs on find(object_id) and find(array_ids) too. any idea dude?