ruby on rails - How to query a polymorphic relationship -

i have jobs table , activities table. 1 job can have many activities. relation polymorphic.

tables:

job         activities ----------- ------------- id          id ...         target_id             target_type             ... 

models pseudo-code:

class job < activerecord::base   # ...   has_many :activities, :as => :target, :dependent => :delete_all   # ... end  class activity < activerecord::base   # ...   belongs_to :target, :polymorphic => true   # ... end 

the state of given job determined state of last activity relates to, below (the last in case last created, can safely order id).

job +-> activity 1 - state: new        |     +-> activity 2 - state: submitted  +--> job state approved     `-> activity 3 - state: approved   | 

how query jobs on given state, using activerecord , rails 3/4?

it (just) occurred me idea to, instead of doing query altogether, use "counter caches" uses , denormalize relationship. store state on jobs table , keeping sync'ed using after_create hook on activity model? along lines:

after_create :update_state  def update_state   target.update_attribute(state: self.state) if target.respond_to?(:state) end 

would viable alternative solve problem in simpler way?

i don't imagine polymorphism issue here (it's way select right data)

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state machine

what using state machine

from looks of it, you're over-engineering models. job has state, not activity, why complicate using model?

if use state machine, state of object handled natively, this:

#app/models/job.rb class job < activerecord::base  state_machine :initial => :new          #states         state :new         state :submitted         state :approved          ### events ###          #submit         event :submit         transition :new => :submitted         end          #approve         event :approve         transition :submitted => :approved         end     end  end 

this handle job state using state attribute in jobs model directly

the important aspect of use of state-machine events:

#state machine functions @job = job.find(id)  @job.state        #-> "new" @job.new?         #-> false @job.submitted?   #-> false @job.approved?    #-> true  @job.submit!      #-> state: "new" -> "submitted" @job.approve!     #-> state: "submitted" -> "approved" 

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scopes

if didn't want remove activity model, may wish use scopes instead

although know can use this, i'm not sure if syntax correct polymorphic association:

#app/models/job.rb class job < activerecord::base     scope :submitted, -> { joins(:activity).where(state: "submitted") }     scope :activity, ->(activity = new) { joins(:activity).where(state: activity) } end