[{"_id":ObjectId("6067640da9a907175caaca34"),"id":101,"name":"Planner","status":"A","height":12,"tags":["mens","womens"],"warehouses":[{"name":"Phoenix","quantity":25},{"name":"Quickshift","quantity":15},{"name":"Poona","quantity":10}]}]

db.collection.aggregate([{"$match":{"name":"Planner"}},{$unwind:"$warehouses"},{$match:{"warehouses.quantity":{"$lt":20}}},{"$group":{_id:"_id",warehouses:{$push:"$warehouses"}}}])