support has_many :through

[active-hash]

support has_many :through

[zilkey]

This can be solved with:

  def foos
    Foo.find bars.map(&:foo_id)
  end

[pivotal-casebook]

This doesn't add support for things like Buzz#foo_ids=, Buzz#foos=, etc., which makes building forms, doing mass assignments, etc. a bit more difficult.

UPDATE: We were experimenting with has_many :through and ActiveHash and learned some things:

When we call Buzz#foo_ids=, ActiveRecord assumes that Foo has columns in order to type cast the arguments into the correct format for the primary key column. It would be better if this could work for all kinds of ActiveModel instead of just ActiveRecord.

Obviously this is a problem with ActiveRecord, not ActiveHash, but this is a great use case to communicate to the ActiveModel / ActiveRecord maintainers.