Embedded documents

As the name suggests, documents embedded inside other documents are called embedded documents. When the parent document is fetched, it also fetches all the embedded documents. This is similar to the composition concept.

The following code shows how we can define an embedded document:

class Address
  include Mongoid::Document

  field :street, type: String
  field :city, type: String
  field :state, type: String
  field :zipcode, type: String
  field :country, type: String

  embedded_in :author
end

And the following code denotes how we can embed it into another model:

class Author
  include Mongoid::Document

  field :name, type: String
  
  has_many :books
  embeds_one :address
end

Now let's have a quick look at how this information was stored in the database. As it was an embedded document, when we fetched the author object, we also got the author's address.

> db.authors.findOne()
{
  "_id" : ObjectId("5143678345db7ca255000001"),
  "address" : {
    "_id" : ObjectId("514367f445db7ca255000003...