Question

“self” here stands for Contact model.
This query will find all completed tasks for a contact.
The Task model has a field/key :assigned_contacts of type Array.
So the query is searching inside the Array.

def assigned_tasks_completed
  self.company.tasks.all(:assigned_contacts => self.id.to_s, :completed => true)
end

How to do this in Mongoid?

Another question:
The equivalent in Mongoid of @contact.set(:a -> a, :b -> b, :c -> c) is update_attributes!

But there is also a method set in Mongoid.
What is the difference between set & update_attributes! in Mongoid ?

Answer 1

I assume your tasks is a separate document. So you can just replace all with where, it will work

def assigned_tasks_completed
  self.company.tasks.where(:assigned_contacts => self.id.to_s, :completed => true)
end

For your another question,

Both mongoid set & update attributes are internally uses mongodb $set. But the difference is mongoid set is only accepts single field update, update_attributes accepts multiple.