Proposed Mongoid::Relations::Proxy#eager_load_ids rewrite

gistfile1.rb

def eager_load_ids(metadata, ids)
  klass, foreign_key = metadata.klass, metadata.foreign_key
  eager_loaded = klass.any_in(foreign_key => ids).entries

  ids.each do |id|
    IdentityMap.clear_many(klass, { foreign_key => id })
  end

  eager_loaded.each do |doc|
    base_id = doc.__send__(foreign_key)
    yield(doc, { foreign_key => base_id })
  end
end