MongoDB query problem

  mongodb, question

Condition: If all username in comments have one equal to xxx (such as Faith), the entire record will be returned.

{
 "_id": ObjectId("5780913bc3666e25282ffdb0"),
 "description": "xx",
 "readed": 2,
 "type": "1",
 "content": "<p>xx</p>",
 "list_img": "xx",
 "comments": [
 {
 "username": "Faith",
 "content": "bbb",
 "avatar": "/static/images/steam_avatar.jpg",
 "sendtime": "2016-07-09 05:53:04"
 },
 {
 "username": "Faith",
 "content": "ccc",
 "avatar": "/static/images/steam_avatar.jpg",
 "sendtime": "2016-07-09 05:53:04"
 },
 {
 "username": "123",
 "content": "zzz",
 "avatar": "/static/images/steam_avatar.jpg",
 "sendtime": "2016-07-09 05:53:04"
 }
 ],
 "author": "admin",
 "sendtime": "2016-07-09 05:52:59",
 "title": "xx"
 }

db.table.find(‘comment.username’, “Fail”)