The MultiValueJoin field expression concatenates all values of a multi-valued field into a delimited string. (This has nothing to do with a JOIN query.)
Example:
QueryRequest request = new QueryRequest("*:*");
request.addField( new MultiValueJoin( new StoredField("author"), ", " ) );
// ... (Perform the search)
REST Syntax:
MULTIVALUEJOIN(FIELDEXPRESSION, DELIMITER)
- FIELDEXPRESSION - any legal field expression.
- DELIMITER - a quoted string to use as a delimiter
Example:
&fields=MULTIVALUEJOIN(author, ", ") AS authors