Dynamic Tag names for InfluxDB output based on field values

Elastic Stack Logstash
1

Hello,

this is not really an issue but more a feature request or idea.
I'm trying to create tag keys in the influx output that are based on a dynamic value.

Let me explain. Here is my message. What I'm interested in as a tag key is the businessTransactions.dimensionNames value "(y) page controller name". This array will always have one item but the associated value of this key is stored in businessTransactions.occurrences.dimensions.

{
  "_index": "dtbtexport-2016.06.28",
  "_type": "logs",
  "_id": "AVWYa_fONUyQIn6JVB9R",
  "_score": null,
  "_source": {
    "businessTransactions": {
      "name": "Page Type User Experience",
      "type": 1,
      "application": "B2C",
      "measureNames": [],
      "dimensionNames": [
        "(y) page controller name"
      ],
      "occurrences": {
        "startTime": 1467141114899,
        "values": [],
        "dimensions": [
          "MiniCart"
        ],
        "actionName": "click on \"Add to cart\"",
        "visitId": 433910,
        "responseTime": 216,
        "cpuTime": 28.232065808963686,
        "execTime": 290.3504825234413,
        "duration": 216,
        "failed": false,
        "clientErrors": 0,
        "convertedBy": [],
        "clientTime": 129.18971347808838,
        "networkTime": 0,
        "serverTime": 86.81028652191162
      }
    }
}

What I'm now trying to do is creating tags based on the dynamic (but finite) value of one field. My intuitive approach was to provide the field in the send_as_tags array:

influxdb {
  host => "localhost"
  db => "dynatrace"
  allow_time_override => "true"
  measurement => "%{[businessTransactions][name]}"
  data_points => {
    "responsetime" => "%{[businessTransactions][occurrences][responseTime]}"
    "businesstransaction" => "%{[businessTransactions][name]}"
    "application" => "%{[businessTransactions][application]}"
    "%{[businessTransactions][measureNames]}" => "%{[businessTransactions][occurrences][values]}"
   "%{[businessTransactions][dimensionNames]}" => "%{[businessTransactions][occurrences][dimensions]}"

   "time" => "%{[businessTransactions][occurrences][startTime]}"
  }
  send_as_tags => ["businesstransaction","application", "%{[businessTransactions][dimensionNames]}"]
}

But this didn't add the tag to influxdb.
Is that because fields are not allowed here or am I'm doing something wrong? Would that be a good usecase or is there another way to achieve this?

Thanks for any feedback!