I had a major bug in my app caused by the following issue: I had a class Foo with a field

references_many :bars, :stored_as => :array

Here's the thing: If I added multiple Bar}}s to a {{Foo, saved the Foo, then fetched it from the database again, the bars array wasn't in the order I expected. I eventually figure out that the root cause was that, although the bar_ids were in the right order, the query used to construct the bars field from those ids was not order-ensuring:

MONGODB my_db['bars'].find({:_id=>{"$in"=>[BSON::ObjectID('4c5c4e12289c7d0e2b000009'), BSON::ObjectID('4c5c4e12289c7d0e2b00000c')]}}, {})

This query will return the right bars, but can (and does) return them in a different order than ObjectID array would suggest. I think it goes without saying that someone who uses :stored_as => :array expects the association to have a consistent order.

In order to ensure that order, I propose that every :stored_as => :array target class have an array index field added (for each parent), and that field be used for an order_by call appended to the any_in call in the query method defined in references_many_as_array.rb:

def query
@query ||= lambda

{ @klass.any_in(:_id => @parent.send(@foreign_key)) }

end

Until this change is implemented, I'll have to use inefficient post-retrieval sorting:

sorted_bars = foo.bars.to_a.sort

{|x,y| foo.bar_ids.index(x.id) <=> foo.bar_ids.index(y.id)}