MongoDB cross-collection query with casbah

Question

I have two collections like follwoing,

customers:
  {id: 1, name: "foo"}
  {id: 2, name: "bar"}
  {id: 3, name: "baz"}

flags:
  {cid: 1}
  {cid: 3}

Then retrieving customers whose flag is on

db.customers.find({id: {$in: db.flags.distinct("cid", {})}})

On shell this works, but I can't do the same using casbah, since casbah does not seem to support querying with function call or local variable.

Answer 1

Of course you can do this in casbah - remember db.flags.distinct returns an iterable that should be converted implicitly to a list for use in $in. Heres a test example for you:

import com.mongodb.casbah.Imports._
val db = MongoClient()("casbahTest")
val customers = db("customers")
val flags = db("flags")

customers.drop()
flags.drop()

// Add some customers
customers += MongoDBObject("_id" -> 1, "name" -> "foo")
customers += MongoDBObject("_id" -> 2, "name" -> "bar")
customers += MongoDBObject("_id" -> 3, "name" -> "baz")

// Add some flags
flags += MongoDBObject("cid" -> 1)
flags += MongoDBObject("cid" -> 3)


// Query
// In JS: db.customers.find({id: {$in: db.flags.distinct("cid", {})}})

// Long hand:
customers.find(MongoDBObject("_id" -> MongoDBObject("$in" -> flags.distinct("cid"))))

// Using Casbahs query dsl to build the MongoDBObject:
customers.find("_id" $in flags.distinct("cid"))