How to build a json object of a Mongoid object with children? - ruby

Question

I have two simple classes
class Band
include Mongoid::Document
field :name, type:String
has_many :members
end
class Member
include Mongoid::Document
field :name, type: String
belongs_to :band
end
After I have created two object for test purposes
Band.create(title: 'New Band')
Band.members.create(name: 'New Member')
I got next db state:
> db.bands.find()
{ "_id" : ObjectId("..."), "title" : "New Band" }
> db.members.find()
{ "_id" : ObjectId("..."), "name" : "New Member", "band_id" : ObjectId("...") }
When I try to build json object of Band object I get data without children:
{"_id":"...","title":"New Band"}
But I need something like that:
{"_id":"...","title":"New Band", "members" : {"_id":"...","title":"New Member"}}
How to build json with children??

Answer 1

You can override serializable_hash:
class Member
include Mongoid::Document
field :name, type: String
belongs_to :band
def serializable_hash(options={})
{
id: id,
name: name
}
end
end
class Band
include Mongoid::Document
field :title, type: String
has_many :members
def serializable_hash(options={})
{
id: id,
title: title,
members: members.inject([]) { |acc, m| acc << m.serializable_hash; acc }
}
end
end
Suppose you have a band with a member:
band = Band.create(title: 'New Band')
band.members.create(name: 'New Member')
In that case band.to_json will return you something like that:
"{\"id\":...,\"title\":\"New Band\",\"members\":[{\"id\":...,\"name\":\"New Member\"}]}"

Answer 2

Try this:
a_band = Band.last
a_band.as_json(methods: [:members])
Mongoid auto-generates helper methods for your relations, and you can include these methods when you build your JSON object. You can use a_band.members to fetch the band's members out of the db, so you can include that method in your JSON object, like any other method on the model.