how to use map-reduce ?

[tasyjean sozoran]

Hi

is map-reduce supported in version .9 ? if so how to use it ?

Thanks!

Cheers,

Tasyjean

[Mark van der Tol]

Hi,

There is no build-in command for MapReduce, but you can make use of the RawCommand to send commands which have no convenience method in ReactiveMongo.

The code for doing a map-reduce would look something like this:

val db: DefaultDB = …

val mapReduceCommand = BSONDocument(

  "mapreduce" -> "inputCollectionName",

  "map" -> BSONString(map),

  "reduce" -> BSONString(reduce),

  "out" -> BSONDocument("replace" -> "outputCollectionName")

)

val result = db.command(RawCommand(mapReduceCommand))

All possible parameters for the mapReduce command are specified here: http://docs.mongodb.org/manual/reference/command/mapReduce/

Mark

[tasyjean sozoran]

Great ! 
thank you

Tasyjean

[Loïc Descotte]

Hi, 

In the MongoDB documentation examples, map and reduce are javascript functions, for example with loops, so I'm no sure ton understand how to fill this in a BSONDocument object.

Do you have an example of mapreduce using ReactiveMongo?

Thanks

Loïc

Le mercredi 17 juillet 2013 15:03:45 UTC+2, tasyjean sozoran a écrit :

Great ! 
thank you

Tasyjean

[Loïc Descotte]

I just found an example on the lichess game code (may be helpful to other people having the same question).  You just need to write a JS function String : 

https://github.com/ornicar/lila/blob/master/modules/message/src/main/ThreadRepo.scala#L28

Definition of the MapReduce helper case class : 

https://github.com/ornicar/lila/blob/master/modules/db/src/main/api/commands.scala#L13