question

I want to keep track of unread messages for private chats for each user. I thought of two ways for doing this, both are pretty similar, the difference is the approach of select and partition key. So one user can have from 1 to 10.000+ contacts. When he's logging in he requests the count of unread messages for all his contacts.
First approach:

create table private_unread_counter (
    from_id text,
    to_id text,
    count counter,
    primary key ((from_id, to_id))
);

This approach means that I'll have to make a select for each contact that an user has. Something like that:

foreach (contact in requestingUserContacts)
{
    unreadMsgsFromContact = select count from private_unread_counter where from_id=contact and to_id=requestingUser
}

Second approach:

create table private_unread_counter (
    from_id text,
    to_id text,
    count counter,
    primary key (to_id)
);

I have one (potentially big) partition for user, and when I want to fetch how many unread messages a user has, I make one select only:

unreadMsgsFromContacts = select (from_id, count) from private_unread_counter where to_id=requestingUser

I'm not sure which one is more appropriate for this. Any answer / info would be appreciated.