Number of Nested objects

[ewolfman]

Hi,
Looking for a way to get the number of nested objects, for querying, sorting etc.
For example:

PUT my-index-000001
{
  "mappings": {
    "properties": {
      "some_id": {"type": "long"},
      "user": {
        "type": "nested",
        "properties": {
          "first": {
            "type": "keyword"
          },
          "last": {
            "type": "keyword"
          }
        }
      }
    }
  }
}

PUT my-index-000001/_doc/1
{
  "some_id": 111,
  "user" : [
    {
      "first" : "John",
      "last" :  "Smith"
    },
    {
      "first" : "Alice",
      "last" :  "White"
    }
  ]
}

How to filter by the number of user (e.g. query fetching all documents with more than XX users).

I was thinking to using a runtime_field but this gives an error:

GET my-index-000001/_search
{
  "runtime_mappings": {
    "num": {
      "type": "long",
      "script": {
        "source": "emit(doc['some_id'].value)"
      }
    },
    "num1": {
      "type": "long",
      "script": {
        "source": "emit(doc['user'].size())" // <- this breaks with "No field found for [user] in mapping"
      }
    }
  }
  ,"fields": [
    "num","num1"
  ]
}

Also tried using aggregations. The following sample gives me the correct doc_count but is there a way to filter by it?

GET my-index-000001/_search
{
  "size": 0,
  "aggs": {
    "aaa": {
      "nested": {
        "path": "user"
      }
    }
  }
}

Would also be nice to know if I can sort the results (e.g. all documents with more than XX and sorted desc by XX).

Thanks.