Strings that can be interpreted as Date cause trouble even if mapped as text

Hello there,

we have an application which allows our customer to upload and index almost any data. We seem to have an issue, if we have a property whose type is "Text", but the input data can be interpreted as a datetime.

First of all, let me show you a part of our mapping, which was received via Kibana Get index/_mappings:

 "fi@Date": {
   "type": "text",
   "fields": {
     "keyword": {
         "type": "keyword"

fi@Date is our property and its type is text. Therefore any string can be used! Our index currently has 2 entries, which look like this (once again partially reduced):

    "_index": "cxcrgygrgemj9cjaofexlq_v1",
    "_source": {
      "filename": "DemoFile01",
      "fi@Date": "2018-10-31T08:25:52",

Second entry:

       "_index": "cxcrgygrgemj9cjaofexlq_v1",
        "_source": {
          "filename": "DemoFile02",
          "fi@Date": "Abc8-10-31T08:25:52"

Note that the first entry has "fi@Date": "2018-10-31T08:25:52",. The right hand side is a datetime representation, but the property fi@Date is defined as a text.

This causes currently two problems:

  1. Using the NEST high level client, we create a request of type

    SearchRequest<Dictionary<string, object>>
    The key of the result dictionary is the name of the property (e.g. "fi@Date") and the value its according value. The NEST client converts this value to DateTime. So we lose some information of the original string (the T is lost). However, if we perform a text search on this property, the correct string is vital. E.g. a TermsQuery does only hit, if we provide the exact string "2018-10-31T08:25:52".
    The second entry "Abc8-10-31T08:25:52" is returned as a normal string and does not yield any problems. The NEST client seems to convert entries based on the result, not on the defined mapping. Is there a way to circumvent this behaviour?

  2. Using the following query in Kibana causes an exception. The same happens with a QueryStringQuery in the NEST Client.

    GET cxcrgygrgemj9cjaofexlq/_search
    "query": {
     "query_string" : {
         "query": "2018-10-31T08:25:52",
         "default_field": "fi@Date",
         "default_operator": "or"

It gives
"reason": "Failed to parse query [2018-10-31T08:25:52]",
"reason": "Cannot parse '2018-10-31T08:25:52': Encountered " ":" ": "" at line 1, column 16.\r\nWas expecting one of:\r\n \r\n ...\r\n ...\r\n ...\r\n "+" ...\r\n "-" ...\r\n ...\r\n "(" ...\r\n "" ...\r\n "^" ...\r\n ...\r\n ...\r\n <FUZZY_SLOP> ...\r\n ...\r\n ...\r\n ...\r\n "[" ...\r\n "{" ...\r\n ...\r\n ",
"caused_by": {
"type": "parse_exception",
"reason": "Encountered " ":" ": "" at line 1, column 16.\r\nWas expecting one of:\r\n \r\n ...\r\n ...\r\n ...\r\n "+" ...\r\n "-" ...\r\n ...\r\n "(" ...\r\n "
" ...\r\n "^" ...\r\n ...\r\n ...\r\n <FUZZY_SLOP> ...\r\n ...\r\n ...\r\n ...\r\n "[" ...\r\n "{" ...\r\n ...\r\n "
Edit: There is no error, if we change slightly change the query, so it does no longer match a datetime e.g. "2018-10-31T08:2552" (removed colon). /Edit

Any ideas? Is this an ElasticSearch Bug? Can I do something to prevent both behaviours?

Version Info
NEST 5.6.5
ElasticSearch.Net 5.6.5
Elastic Search on Server 5.5

Kind regards,


I was able to narrow the first part down (automapping to DateTime object):
It is default Json Behaviour to map any DateTime-ish string to a DateTime object.
(Discussion around this can be found here:

In Json this can be fixed via Serializersettings. In Nest this would look like:

 mEsClientConnectionSettings = new ConnectionSettings(connectionPool, connection, new SerializerFactory((settings, values) =>
  settings.NullValueHandling = NullValueHandling.Ignore;
  settings.TypeNameHandling = TypeNameHandling.None;
  settings.DateParseHandling = DateParseHandling.None;

However this does not help me. The Client still deserializes my string into a datetime object. I checked the specific client via Debugging and its serializersettings does have the DateParseHandling = DateParseHandling.None; set.

It does work in a small testprogram with NewtonSoft.Json:

JsonSerializerSettings settings = new JsonSerializerSettings
    DateParseHandling = DateParseHandling.None
  var obj = JsonConvert.DeserializeObject<Dictionary<string, Object>>("{\"MyKey\" : \"2018-10-31T08:25:52\"}", settings);

Any ideas how to fix this in Nest?

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