Using the m/r function with an $or query appears to be impossible right now. We are using the query below for one of our map reduces and are getting this error:

SyntaxError: invalid property id

mongo mentions line 78; below are lines 73-84:

db.runCommand({
 mapreduce : "clients_raw",
 map : m,
 reduce : r,
 query : {
  { "_id.DAY": "2012-06-22" , $or : [ {"_id.CLIENT_ID": 123},  {"_id.CLIENT_ID": 456} ] }
 },
 out : {
  merge : "clients"
 },
 finalize : f
});

Running the query through a find generates the results we expect; removing the $or condition, too, generates results we expect. It seems as if combining $or with another field however, is not possible at this point.