Calling update_attributes on an embedded document, where one of the hash members is itself a second embedded document, produces an incorrect mongo query and as a result fails to persist the nested document.

For example, using these documents:

Person
embeds_many Addresses

Address
embedded_in Person
embeds_many Locations

Location
embedded_in Address

With this pseudo-code:

p = Person.create( name: "Jimmy", addresses: [ { city: 'Buffalo', locations: [

{ name: 'Work' }

] } ] )

attributes = { city: 'New York', locations: [

{ name: 'Home' }

] }
p.addresses.first.update_attributes( attributes )

puts "#

{p.addresses.first.city}

" # Prints "New York", as expected
puts "#

{p.addresses.first.locations.first.name}

" # Prints "Home", as expected

new_p = p.reload
puts "#

{new_p.addresses.first.locations.first.name}

" # Prints "Work" – wrong

The third line prints the old value ("Work"). Observing the Mongo driver, this query is emitted:

MONGODB (0ms) mongoid_test['people'].update(

{"_id"=>BSON::ObjectId('4f7380bb51e63a588000009a'), "addresses._id"=>"tauentzienstr"}

, {"$set"=>{"addresses.0.city"=>"Berlin", "locations"=>[

{"_id"=>BSON::ObjectId('4f7380bb51e63a588000009b'), "name"=>"Home"}

]}})

If this weren't weird enough, inspecting the document after running the above code shows that the "locations" collection has been added to the people document, where it contains the correct values:

puts "#

{new_p['locations']}

" # Should be nil, but prints out the locations array

I've written some specs that test for this bug and will send a pull request for them shortly.