Topic: How to Access CouchDB documents by property in RoR CouchRest Gem

I'm using CouchRest model, my CouchDB contains many documents and has documentType as Survey, Response, Questions, Demo

What i need is accessing all document which has documentType as Survey, how can i do this in Rails 3 using CouchRest model?

here is my model

class Android < CouchRest::Model::Base
  property :description, String
  property :_id, String
  property :_rev, String
  property :documentType, String

  view_by :documentType
end

and i tried executing as follows in rails IRB console

irb(main):006:0> me=Android.find_by_documentType("Survey")

But It's not working for me as expected, it's showing error like this

OkJson::Error: cannot encode CouchRest::Design: #<CouchRest::Design _id:    
 "_design/Android", language: "javascript", views: {"all"=>{
 "map"=>"function(doc) {\n if (doc['type'] == 'Android')
 {\n    emit(doc['_id'],1);\n}\n}"}, "by_documentType"=>{"map"=>"function(doc) 
 {\n  if ((doc['type'] == 'Android') && (doc['documentType'] ...........

What is the problem here? am i doing it in correct way? please help me