No Pressure

Mongo and Mongoid checking if an array is empty

First attempt in Mongoid:

{ foo: { $not: { $size: 0 } } }

This gets translated to mongoid with the following:

User.where(:foo.size => 0)

:) ENJOY!!

How to check if a document exists in Mongo and Mongoid

First step Mongo shell query:

db.yourcollection.find({ 'deleted_at' : { '$exists' : true }})

This query in mongo shell will actually pull all the records for which the field deleted_at is not null.

@posts = Posts.where(:created_at.lte => (Date.today - 2), :author => “BlogMaster”, :likings.exists => false, :comments.exists => false)

This instead will pull all the records older than 2 days ago, with author BlogMaster and for which we don’t have any likings nor comments.

Enjoy!

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]