[{service:[{_id:1,provider_id:"provider1",service_code:"code1",price:20},{_id:2,provider_id:"provider1",service_code:"code2",price:20},{_id:3,provider_id:"provider1",service_code:"code3",price:20},{_id:4,provider_id:"provider2",service_code:"code1",price:10},{_id:5,provider_id:"provider2",service_code:"code2",price:20},{_id:6,provider_id:"provider3",service_code:"code1",price:20}]}]

db.collection.aggregate({"$unwind":"$service"},{"$match":{"service.provider_id":"provider1"}})