Failed to parse rules expression field requires an array – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch tries to parse a rule expression and encounters a field that requires an array but doesn’t find one. This could be due to incorrect data formatting or a mismatch between the expected and actual data structure. To resolve this issue, you can: 1) Check the data you’re trying to index and ensure it matches the expected format. 2) Review your mapping and make sure it aligns with the data structure. 3) If you’re using a script or automated process to generate data, verify that it’s producing the correct output.

This guide will help you check for common problems that cause the log ” failed to parse rules expression. field [{}] requires an array ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “failed to parse rules expression. field [{}] requires an array” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 while (parser.nextToken() != XContentParser.Token.END_ARRAY) {
 return list;
 } else {
 throw new ElasticsearchParseException("failed to parse rules expression. field [{}] requires an array"; field);
 }  private FieldExpression.FieldValue parseFieldValue(XContentParser parser) throws IOException {
 return switch (parser.currentToken()) {