Case Insensitive Sort on a Keyword Field in 5.x

[Vadim_Rybak]

We are using Elasticsearch 5.
I have a field city using a custom analyzer and the following mapping.

Analyzer

       "analysis": {
          "analyzer": {
            "lowercase_analyzer": {
              "filter": [
                "standard",
                "lowercase",
                "trim"
              ],
              "type": "custom",
              "tokenizer": "keyword"
            }
}

Mapping

  "city": {
    "type": "text",
    "analyzer": "lowercase_analyzer"
  }

I am doing this so that I can do a case insensitive sort on the city field. Here is an example query that I am trying to run

{ 
  "query": {
    "term": {
      "email": {
        "value": "some_email@test.com"
      }
    }
  },
"sort": [
    {
      "city": {
        "order": "desc"
      }
    }
  ]
}

Here is the error I am getting:

"Fielddata is disabled on text fields by default. Set fielddata=true
on [city] in order to load fielddata in memory by uninverting the
inverted index. Note that this can however use significant memory."

I don't want to turn on FieldData and incur a performance hit in Elasticsearch. I would like to have a Keyword field that is not case sensitive, so that I can perform more meaningful aggregations and sorts on it. Is there no way to do this?

[dadoonet (David Pilato)]

In 5.0 and 5.1 you have to use a type keyword but for now you can't analyze the text it contains. See

Issue: Support analyzer for keyword type

In the meantime, you have to format your document if you don't want to use fielddata and creates a new field out of the first one like city_sort.

To do that, you can define an ingest pipeline with a lowercase processor which generates that at index time.
Note that this will come back as part of the _source though.

Not ideal but at least a workaround.