Attributes/Persistence logic does not support Mongoid HABTM

[Startouf]

In Mongoid, has_and_belongs_to_many means storing an array of IDs in the document.
So the usual flow of updating a model attribute with a key doesn't make too much sense. Instead we need to add/remove keys`

class Tag
  has_many :profiles
end

class Profile
  has_and_belongs_to :tags
end

tags = FactoryGirl.create_list(:tags, 2)
profile = Profile.create(tags: tags)
profile.as_document
#=>
 {
 "_id"=>BSON::ObjectId('593ab877aba9cf64dbd09582'),
 "tag_ids"=>[
    BSON::ObjectId('592da071aba9cf502513d424'), 
    BSON::ObjectId('592da081aba9cf502513d426')
  ]
}

To begin with, there is a somewhat hardcoded list of has_many/belongs_to in the persistence class
https://github.com/jsonapi-suite/jsonapi_compliable/blob/master/lib/jsonapi_compliable/util/persistence.rb#L98

that should be moved to the adapter, so for mongoid I can override/implement it with a :habtm

Then for the persistence flow itself, I had to monkeypatch the update_foreign_key logic to support writing the list of habtm IDs

def update_foreign_key(parent_object, attrs, x)
    ...
    elsif x[:sideload].type == :habtm
      (attrs[x[:foreign_key]] ||= []) << parent_object.send(x[:primary_key]).to_s
    ...

[richmolj]

I'd like a clean pattern the adapter can override, even ActiveRecord has a tag_ids= API. For this specific issue in the short term, though, maybe it would be better to expose a tag_ids attribute and update it that way instead of sideposting?

[Startouf]

Hey yes this is what I've been doing, it's much easier. It won't support partial disassociation/association (each time the whole list must be sent again) nor destroys, but it's somewhat ok for my specific use case (I'm not even sure destroys in habtm actually make sense)