db={"category":[{"_id":"101","categoryName":"Tesla"},{"_id":"102","categoryName":"BMW"}],"car":[{"_id":801,"categoryId":"101","carName":"Model S","description":"This is model s","views":10,"driverId":"201"},{"_id":802,"categoryId":"102","carName":"X1","description":"This is x1","views":20,"driverId":"201"},{"_id":803,"categoryId":"101","carName":"Model X","description":"This is model x","views":30,"driverId":"202"},{"_id":804,"categoryId":"101","carName":"Model 3","description":"This is model 3","views":40,"driverId":"202"},{"_id":805,"categoryId":"101","carName":"CyberTruck","description":"This is CyberTruck","views":50,"driverId":"202"}],"driver":[{"_id":"201","name":"Mary"},{"_id":"202","name":"Tom"}]}

db.category.aggregate([{$lookup:{from:"car",localField:"_id",foreignField:"categoryId",as:"cars"}},{$project:{_id:1,categoryName:1,cars:{$slice:["$cars",3]}}},{$project:{categoryName:1,"cars.carName":1,"cars.views":1,"cars.driverId":1}}])