[{item:"journal",instock:[{warehouse:"A",qty:5,items:null},{warehouse:"C",qty:15,items:[{name:"alexa",age:26},{name:"Shawn",age:26}]}]}]

db.collection.aggregate([{$match:{"instock.items.name":"alexa"}},{$unwind:"$instock"},{$project:{"item":"$item",qty:"$instock.qty",warehouse:"$instock.warehouse",items:{$filter:{input:"$instock.items",as:"item",cond:{$eq:["$$item.name","alexa"]}}}}},{$group:{_id:"$_id",instock:{$push:"$$ROOT"}}}])