[{_id:1,description:"DESCRIPTION ARTICLE AB",article_code:"AB",purchase:[{company:1,cost:1},{company:2,cost:2},{company:3,cost:3}],stock:[{country:"01",warehouse:{code:"02",units:10}},{country:"02",warehouse:{code:"02",units:8}}]},{_id:2,description:"DESCRIPTION ARTICLE AC",article_code:"AC",purchase:[{company:1,cost:1},{company:2,cost:2},{company:3,cost:3}],stock:[{country:"01",warehouse:{code:"01",units:20}},{country:"02",warehouse:{code:"02",units:28}}]}]

db.collection.find({"stock.country":"01"},{stock:{$slice:1}})