I'm designing a social network system like twitter, and users will receive notifications, I'm going to persist notifications to mongodb. We will keep 100 notification for each user at most and the only field would be update is `read`(wether user has read the notification). So I am wondering wether using multi document as blow

```
{"userId":1, "content":"some msg", "read":true..}
{"userId":1, "content":"another msg", "read":true..}

```

or using embedded documents like this: 

```
{"userId":1, "noficications":[{"content":"some msg", "read": true},{"content":"another msg", "read":true}]}

```