When we use mongoid_search we need to include Mongoid::Search in our model and we need to specify for which fields we want to search with the help of search_in. When we specify fields in search_in it adds _keyword field in document and when i created object from console _keyword array was consisting of keywords ex email is abc@gmail.com then it had keywords abc, gmail, com.. when we request comes for search it searches in keywords as i used full_text_search method if it finds complete word in _keywords it returns that object