[{"_id":ObjectId("5ea31dce0e4d4b09e4db0cd6"),"_class":"com.litmus7.river.commons.common.model.survey.Result","survey_id":"5ea30df40e4d4b4de4d7b6d7","survey_question":[{"question_id":"5ea30df40e4d4b4de4d7b6d2","question_options":[{"option_id":"5ea30df40e4d4b4de4d7b6d1","user_id":["111","222"]},{"option_id":"5ea30df40e4d4b4de4d7b6cf","user_id":["333","444"]}]},{"question_id":"5ea30df40e4d4b4de4d7b6d6","question_options":[{"option_id":"5ea30df40e4d4b4de4d7b6d3","user_id":["111","222"]},{"option_id":"5ea30df40e4d4b4de4d7b6d5","user_id":["333","444"]}]}]}]

db.collection.aggregate([{$unwind:"$survey_question"},{$match:{"survey_question.question_options.option_id":"5ea30df40e4d4b4de4d7b6d1"}},{$project:{count:{$size:"$survey_question.question_options.user_id"}}}])