Must be a string – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 8.3-8.9

Briefly, this error occurs when Elasticsearch expects a string value for a particular field, but it receives a different data type. This could be due to incorrect data input or mapping. To resolve this issue, ensure that the data type of the input matches the expected data type in the Elasticsearch mapping. If the mapping is incorrect, you may need to reindex your data with the correct mapping. Alternatively, you can convert the non-string data into a string before indexing it into Elasticsearch.

This guide will help you check for common problems that cause the log ” [{}] must be a string ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “[{}] must be a string” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 String parseField(XContentSubParser subParser) throws IOException {
 if (subParser.currentToken() == XContentParser.Token.VALUE_STRING) {
 return subParser.text();
 } else {
 throw new ElasticsearchParseException("[{}] must be a string"; name);
 }  private static class DoubleFieldParser extends FieldParser {


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