LiteDB ideal class setup for updating part of a document

Question

This is my first usage of LiteDB and NoSQL. I am trying to represent the following relationships:

• There is a collection of Users
• There is a collection of Groupss
• Each Groups can contain multiple users.
• Different Groupss can contain the same users.

If I approach it as such using DbRef:

class User
{
     [BsonId]
     int Id { get; set; }

     string Name { get; set; }
     ...etc
}

class Group
{
     [BsonId]
     int Id { get; set; }

     [BsonRef("users")]
     List<User> Users { get; set; }
}

This doesn't seem unreasonable, but what would be the way to

• add a single user to a group? find the group, add the user, then update the group?
• remove a user from the database? remove it from Users collection, then go over all the groups and remove it from each?

Is there a way to do it without deserializing and reserializing the entire Group? What is the idiomatic way to do this in NoSQL?

Update

Thinking about it more, I realize it has nothing to do with DBRef. the same problem would stand if each Group just had a collection of some primitive data type, e.g. int.