For example, the collection test has the following document format

{
 "_id" : ObjectId("123456"),
 "name" : "test",
 "body" : [
 {
 "hash" : "123123123"
 }
 ]
 }

At this time, if you want to create an index for the hash key, how should you create it? the value of body is an array, so it’s a bit confusing.