JSONPath and PDI's MongoDB Input step

[psema4]

I wonder if someone could clarify the relationship between PDI's MongoDB Input Step and JSONPath. There are a couple forum posts that refer to this reference but I'm not sure why simple looking queries aren't working.

For example, I need to transform some user documents stored in a mongo collection, using a document structure like:

{
  "_id" : ObjectId("5d7a5034041ba5fe61010003"),
  "classID" : "14",
  "userID": "10",
  "otherField": "other data..."
}

If I query for a specific user id, I have no trouble:

{ "$query" : { "userID" : "10" } }

However if I try to use a wildcard, I get no rows. I would expect the following JSONPath queries to return a row (containing one string field) for each user document in the collection but instead they fail:

{ "$query" : "$..*" }

{ "$query" : { "userID" : "*" } }

The wiki has some information on basic operations but precious little on the query syntax. Any suggestions, pointers or clarifications would be greatly appreciated.

[psema4]

Found some additional query samples which are enough for my immediate needs. If there's a tutorial or article on Mongo + PDI somewhere, I'd be interested in hearing about it.