No Pressure

Mongoid recursively embedding

This is a note for myself for a project I am actually working on that I thought could be useful to share :)

More info here.

CYCLIC RELATIONS on MONGODB WITH MONGOID

A document can recursively embed itself using recursively_embeds_many, which provides accessors for the parent and children.

class Tag
  include Mongoid::Document
  recursively_embeds_many
  field :name
end

programming = Tag.new(:name => 'programming')
ruby = programming.child_tags.build(:name => 'ruby')
python = programming.child_tags.build(:name => 'python')

programming.child_tags  # [ruby, python]
ruby.parent_tag         # [programming]
python.parent_tag       # [programming]

Updating embedded child objects when the parent object is saved.

Mongoid has added a tag which automatically makes callbacks for embedded child objects when the parent object is saved.

You can find it at the end of the mongoid documentation on embedding.

class Post
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::Paranoia

  embeds_many :comments, cascade_callbacks: true
  accepts_nested_attributes_for :comments
end

Nested hash in ruby

Ever wondered how to create nested hash in ruby?

Here it is:

1.9.3p125 :001 > a = Hash.new{|h,k| h[k]=Hash.new(&h.default_proc) }

 => {} 

1.9.3p125 :002 > a[2][1] = 2

 => 2 

1.9.3p125 :003 > a[2][2][3] = 2

 => 2 

1.9.3p125 :004 > a[2][2][4] = 5

 => 5 

1.9.3p125 :005 > a[3][1][1][1] = 7

 => 7 

1.9.3p125 :006 > a

 => {2=>{1=>2, 2=>{3=>2, 4=>5}}, 3=>{1=>{1=>{1=>7}}}} 

:) sweet!

Ruby headaches pills

If:

script/rails generate controller Hello

Is failing, try to remember that you have probably installed more than one version of rails in your history, so you might need to call:

rvm use 1.9.1 —default :)