Play ReactiveMongo - exception when trying to find one document - mongodb

Question

I've started using Play and the Play-ReactiveMongo plugin and testing for a 404 response on a GET "document by id" scenario. Unfortunately instead of Play returning a 404 NotFound response I get this exception:
java.util.NoSuchElementException: JsError.get
at play.api.libs.json.JsError.get(JsResult.scala:11) ~[play_2.10.jar:2.1.1]
at play.api.libs.json.JsError.get(JsResult.scala:10) ~[play_2.10.jar:2.1.1]
at play.modules.reactivemongo.json.collection.JSONGenericHandlers$StructureBufferWriter$.write(jsoncollection.scala:44) ~[play2-reactivemongo_2.10-0.9.jar:0.9]
at play.modules.reactivemongo.json.collection.JSONGenericHandlers$StructureBufferWriter$.write(jsoncollection.scala:42) ~[play2-reactivemongo_2.10-0.9.jar:0.9]
at reactivemongo.api.collections.GenericQueryBuilder$class.reactivemongo$api$collections$GenericQueryBuilder$$write(genericcollection.scala:323) ~[reactivemongo_2.10-0.9.jar:0.9]
at reactivemongo.api.collections.GenericQueryBuilder$class.cursor(genericcollection.scala:333) ~[reactivemongo_2.10-0.9.jar:0.9]
The getById function below successfully returns a single document if the id parameter matches an existing document, but an exception on the line "one[JsValue]" if document not found.
Route file:
GET /items/:id controllers.ItemsController.getById(id: String)
Controller object:
object ItemsController extends Controller with MongoController {
def itemsCollection: JSONCollection = db.collection[JSONCollection]("items")
def getById(id: String) = Action {
Async {
val query = Json.obj("_id" -> Json.obj("$oid" ->id))
val futureItem = itemsCollection.
find(query).
one[JsValue]
futureItem.map {
case Some(item) => Ok(item)
case None => NotFound(Json.obj("message" -> "No such item"))
}
}
}
}
Maybe I missed something in the docs?
There is partial example documented here:
https://github.com/sgodbillon/reactivemongo-demo-app#simple-query
The mandubian coast-to-coast example handles BadRequest as well NotFound scenario, but code is maybe out of date as it doesn't use the newer looking find(...).one[...] semantics?
http://mandubian.com/2013/01/13/JSON-Coast-to-Coast/#action-get

Answer 1

Turns out the ID needs to be a valid ObjectId, e.g. 24 characters and no illegal tokens.
If the ID is valid but does not reference an existing document then I get a 404 as expected.
If the ID format is invalid (e.g. only 12 characters or contains illegal tokens like '#') then I get an Exception.
When I compare behaviour with an equivalent Node.js + Mongoose app results are very similar.
For example if deliberately querying with a malformed 12 character ID I get this stacktrace in Node:
{ message: 'Cast to ObjectId failed for value "51bded70543f" at path "_id"',
name: 'CastError',
type: 'ObjectId',
value: '51bded70543f',
path: '_id' }
Not sure if this exception is the underlying error in the Play app too but it gave enough of a clue.
The answer would seem to be pre-validate IDs before calling find(query).one[T].