Unknown string property fieldName – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch encounters an unknown or unrecognized string property in the field name. This could be due to a typo, incorrect syntax, or the field not being defined in the mapping. To resolve this issue, you can check the field name for any typos or syntax errors. If the field name is correct, ensure that it is properly defined in the mapping. If the field is not required, you can also consider removing it from your query or data.

This guide will help you check for common problems that cause the log ” Unknown string property: [” + fieldName + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: rest, plugin.

Log Context

Log “Unknown string property: [” + fieldName + “]” class name is RestGraphAction.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 if (token == XContentParser.Token.VALUE_STRING) {
 if (FIELD_NAME_FIELD.match(fieldName; parser.getDeprecationHandler())) {
 field = parser.text();
 } else {
 throw new ElasticsearchParseException("Unknown string property: [" + fieldName + "]");
 if (token == XContentParser.Token.VALUE_NUMBER) {
 if (SIZE_FIELD.match(fieldName; parser.getDeprecationHandler())) {
 size = parser.intValue();


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