Failed to parse More Like This item field fields must be an array – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7.16-7.17

Briefly, this error occurs when the “fields” parameter in a More Like This (MLT) query is not formatted as an array. Elasticsearch expects the “fields” parameter to be an array, even if it contains only one item. To resolve this issue, ensure that the “fields” parameter is formatted as an array. For example, instead of “fields”: “field1”, use “fields”: [“field1”]. If you have multiple fields, separate them with commas within the array, like “fields”: [“field1”, “field2”].

This guide will help you check for common problems that cause the log ” failed to parse More Like This item. field [fields] must be an array ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: index, query.

Log Context

Log “failed to parse More Like This item. field [fields] must be 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) {
 item.fields(fields.toArray(new String[fields.size()]));
 } else {
 throw new ElasticsearchParseException("failed to parse More Like This item. field [fields] must be an array");
 } else if (PER_FIELD_ANALYZER.match(currentFieldName; parser.getDeprecationHandler())) {
 } else if (ROUTING.match(currentFieldName; parser.getDeprecationHandler())) {
 item.routing = parser.text();


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