Database
db={"Products":[{"name":"My Product 01","description":"This is an excelent product","tags":["AA","BBBB","C","DDDDDDDDDDD"]},{"name":"My Product 02","description":"This is an excelent product","tags":["AA","BBBB","C","ZZZZZZZZZZZ"]}]}
Query
db.Products.aggregate([{"$unwind":"$tags"},{"$set":{"length":{"$strLenCP":"$tags"}}},{"$setWindowFields":{"partitionBy":null,"sortBy":{"length":-1},"output":{"rank":{$rank:{}}}}},{"$match":{rank:1}}])