How to enforce unique embedded document in mongoid

Question

I have the following model

class Person 
  include Mongoid::Document
  embeds_many :tasks
end

class Task
  include Mongoid::Document
  embedded_in :commit, :inverse_of => :tasks
  field :name
end

How can I ensure the following?

person.tasks.create :name => "create facebook killer"
person.tasks.create :name => "create facebook killer"

person.tasks.count == 1

different_person.tasks.create :name => "create facebook killer"
person.tasks.count == 1
different_person.tasks.count == 1

i.e. task names are unique within a particular person

---

Having checked out the docs on indexes I thought the following might work:

class Person 
  include Mongoid::Document
  embeds_many :tasks

  index [
      ["tasks.name", Mongo::ASCENDING], 
      ["_id", Mongo::ASCENDING]
  ], :unique => true
end

but

person.tasks.create :name => "create facebook killer"
person.tasks.create :name => "create facebook killer"

still produces a duplicate.

---

The index config shown above in Person would translate into for mongodb

db.things.ensureIndex({firstname : 1, 'tasks.name' : 1}, {unique : true})

Answer 1

Can't you just put a validator on the Task?

validates :name, :uniqueness => true

That should ensure uniqueness within parent document.

Answer 2

Indexes are not unique by default. If you look at the Mongo Docs on this, uniqueness is an extra flag.

I don't know the exact Mongoid translation, but you're looking for something like this:

db.things.ensureIndex({firstname : 1}, {unique : true, dropDups : true})