Rails 3 query matching attribute of has_one association that is a subset of has_many association
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The title is confusing, but allow me to explain. I have a Car model that has multiple datapoints with different timestamps. We are almost always concerned with attributes of its latest status. So the model has_many statuses, along with a has_one to easily access it's latest one:

    class Car < ActiveRecord::Base
      has_many :statuses, class_name: 'CarStatus', order: "timestamp DESC"
      has_one :latest_status, class_name: 'CarStatus', order: "timestamp DESC"

      delegate :location, :timestamp, to: 'latest_status', prefix: 'latest', allow_nil: true

      # ...
    end

To give you an idea of what the statuses hold:

    loc = Car.first.latest_location   # Location object (id = 1 for example)
    loc.name                          # "Miami, FL"

Let's say I wanted to have a (chainable) scope to find all cars with a latest location id of 1. Currently I have a sort of complex method:

    # car.rb
    def self.by_location_id(id)
      ids = []
      find_each(include: :latest_status) do |car|
        ids << car.id if car.latest_status.try(:location_id) == id.to_i
      end
      where("id in (?)", ids)
    end

There may be a quicker way to do this using SQL, but not sure how to only get the latest status for each car. There may be many status records with a location_id of 1, but if that's not the latest location for its car, it should not be included.

To make it harder... let's add another level and be able to scope by location name. I have this method, preloading statuses along with their location objects to be able to access the name:

    def by_location_name(loc)
      ids = []
      find_each(include: {latest_status: :location}) do |car|
        ids << car.id if car.latest_location.try(:name) =~ /#{loc}/i
      end
      where("id in (?)", ids)
    end

This will match the location above with "miami", "fl", "MIA", etc... Does anyone have any suggestions on how I can make this more succinct/efficient? Would it be better to define my associations differently? Or maybe it will take some SQL ninja skills, which I admittedly don't have.