Scala Days 2011 - Rogue: A Type-Safe DSL for MongoDB

rogue:a scala dsl for mongodbScalaDays 2011 - 6/2/2011Jason Liszka (@jliszka)Jorge Ortiz (@jorgeortiz85)

what is foursquare?location-based social network - “check-in” to bars,restaurants, museums, parks, etc friend-finder (where are my friends right now?) virtual game (badges, points, mayorships) city guide (local, personalized recommendations) location diary + stats engine (where was I a year ago?) specials (get rewards at your favorite restaurant)

foursquare: the numbers>9M users~3M checkins/day>15M venues>400k merchants>60 employees

foursquare: the tech Nginx, HAProxy Scala, Lift MongoDB, PostgreSQL (legacy) (Kestrel, Munin, Ganglia, Python, Memcache, ...) All on EC2

what is mongodb?fast, schema-less document storeindexes & rich queries on any fieldsharding, auto-balancingreplicationgeo-indexes

mongodb: our numbers8 clusters some sharded, some not some master/slave, some replica set~40 machines (68.4GB, m2.4xl on EC2)2.3 billion records~15k QPS

mongodb: bsonjson++binary wire formatmore built-in types: objectid date regex bina

mongodb: bson example{ “_id” : { “oid” : “4ddbd194686148110d5c1ccc” }, “venuename” : “Starbucks”, “mayorid” : 464, “tags” : [“coffee”, “wifi”, “snacks”], “latlng” : [39.0, -74.0]}

mongodb: query example{ “mayorid” : { “$lte” : 100 }, “venuename” : “Starbucks”, “tags” : “wifi”, “latlng” : { “$near” : [39.0, -74.0] }}{ “_id” : -1 }

mongodb: query exampleval query = (BasicDBOBjectBuilder .start .push(“mayorid”) .add(“$lte”, 100) .pop .add(“veneuname”, “Starbucks”) ... .get)

rogue: a scala dsl for mongo type-safe all mongo query features logging & validation hooks pagination index-aware cursors http://github.com/foursquare/rogue

rogue: schema exampleclass Venue extends MongoRecord[Venue] { object _id extends ObjectIdField(this) object venuename extends StringField(this) object mayorid extends LongField(this) object tags extends ListField[String](this) object latlng extends LatLngField(this)}object Venue extends Venue with MongoMetaRecord[Venue]

rogue: code exampleval vs: List[Venue] = (Venue where (_.mayorid <= 100) and (_.venuename eqs “Starbucks”) and (_.tags contains “wifi”) and (_.latlng near (39.0, -74.0, Degrees(0.2)) orderDesc (_._id) fetch (5))

rogue: BaseQueryclass BaseQuery[M <: MongoRecord[M], R, Ord, Sel, Lim, Sk](...) { def where[F](clause: M => QueryClause[F]): ... ...}

rogue: QueryFieldclass QueryField[V, M <: MongoRecord[M]] (val field: Field[V, M]) { def eqs(v: V) = new EqClause(...) def neqs(v: V) = ... def in[L <% List[V]](vs: L) = ... def nin[L <% List[V]](vs: L) = ... def exists(b: Boolean) = ...}

rogue: implicitsField[F, M] => QueryField[F, M]Field[LatLong, M] => GeoQueryField[M]Field[List[F], M] => ListQueryField[F, M]Field[String, M] => StringQueryField[M]Field[Int, M] => NumericQueryField[Int, M]Field[Double, M] => NumericQueryField[Double, M]...

rogue: selectval vs: List[(Long, Int)] = (Venue where (_.venuename eqs “Starbucks”) select (_.mayorid, _.mayorCheckins) fetch ())

rogue: selectclass BaseQuery[M <: MongoRecord[M], R, Ord, Sel, Lim, Sk](...) { def select[F1, F2]( f1: M => Field[F1, M], f2: M => Field[F2, M]): BaseQuery[M, (F1, F2), ...] = ... ...}

rogue: select problemsval vs: List[???] = (Venue where (_.venuename eqs “Starbucks”) select (_.mayorid, _.mayorCheckins) select (_.venuename) fetch ())

rogue: limit problemsval vs: List[Venue] = (Venue where (_.venuename eqs “Starbucks”) limit (5) limit (100) // (???) fetch ())

rogue: more limit problems(Venue where (_.venuename eqs “Starbucks”) orderAsc (_.total_checkins) limit (5) bulkDelete_!!)// How many Venues got deleted?

rogue: phantom types Sel =:= Selected, Unselected Ord =:= Ordered, Unordered Lim =:= Limited, Unlimited Sk =:= Skipped, Unskippedhttp://james-iry.blogspot.com/2010/10/phantom-types-in-haskell-and-scala.html

rogue: phantom typesabstract sealed class Orderedabstract sealed class Unorderedabstract sealed class Selectedabstract sealed class Unselectedabstract sealed class Limitedabstract sealed class Unlimitedabstract sealed class Skippedabstract sealed class Unskipped

rogue: initializing phantomsclass BaseQuery[M <: MongoRecord[M], R, Ord, Sel, Lim, Sk](...) { ...}def dfltQuery[M <: MongoRecord[M]](rec: M) = new BaseQuery[M, M, Unordered, Unselected, Unlimited, Unskipped](...)

rogue: select phantomclass BaseQuery[M <: MongoRecord[M], R, Ord, Sel, Lim, Sk](...) { def select[F1, F2]( f1: M => Field[F1, M], f2: M => Field[F2, M]) (implicit ev: Sel =:= Unselected): BaseQuery[M, (F1, F2), Ord, Selected, Lim, Sk] = ... ...}

rogue: =:=sealed abstract class =:=[From, To] ...implicit def tpEquals[A]: A =:= A = ...

rogue: select solutionsval vs: List[???] = (Venue where (_.venuename eqs “Starbucks”) select (_.mayorid, _.mayorCheckins) select (_.venuename) fetch ())// won’t compile!

rogue: limit solutions(Venue where (_.venuename eqs “Starbucks”) orderAsc (_.total_checkins) limit (5) bulkDelete_!!)// won’t compile!

rogue: index-awareval vs: List[Checkin] = (Checkin where (_.userid eqs 646) and (_.venueid eqs vid) fetch ())

rogue: index-awareval vs: List[Checkin] = (Checkin where (_.userid eqs 646) and (_.venueid eqs vid) // hidden scan! fetch ())

rogue: index-awareval vs: List[Checkin] = (Checkin where (_.userid eqs 646) // known index scan (_.venueid eqs vid) // known scan fetch ())

rogue: logging & validation logging: slf4j Tracer validation: radius, $in size index checks

rogue: paginationval query: Query[Venue] = ...val vs: List[Venue] = (query .countPerPage(20) .setPage(5) .fetch())

rogue: cursorsval query: Query[Checkin] = ...for (checkin <- query) { ... f(checkin) ...}

rogue: future directions iteratees for cursors compile-time index checking select partial objects generate full javascript for mapreduce

we’re hiring (nyc & sf)http://foursquare.com/jobs @jliszka, @jorgeortiz85

http://paper.li	7
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Scala Days 2011 - Rogue: A Type-Safe DSL for MongoDB

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