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How to use self referential N-M relationship to make 2 users friends using RedBean PHP ORM?

I am working with PHP and [RedBean PHP ORM](https://redbeanphp.com/index.php). I have a table `user` like so:

```
id | username
---|---------
 1 | Alice
 2 | Bob
```

I want Alice and Bob to become friends. So I want to create M-M junction table `friend` that will look something like this:

```
id | friend_1_id | friend_2_id
---|-------------|------------
 1 |           1 |           2
```

`friend_1_id` and `friend_2_id` should be a foreign key reference to `user`.

In RedBean PHP ORM documentation at the bottom of [Many-to-Many](https://redbeanphp.com/index.php?p=/many_to_many) page there is a section titled "[Self referential N-M](https://redbeanphp.com/index.php?p=/many_to_many#self_referential_many_to_many)". Here is the content of that section:

 > You can have a shared list containing beans of the same type as the owner of the list: 
\
\
`$friends = $friend->sharedFriend;`
\
\
In this case RedBeanPHP will operate in a special self-referential many-to-many relationship mode. It will not only retrieve all friends of $friend, but also all other friends that are associated with $friend.

I don't find this section to be informative enough.
I suspect that this is exactly what I need, however, I cannot figure out how to make it work. Here is what I tried:

```
$u1 = R::findOne("user", "id = 1");
$u2 = R::findOne("user", "id = 2");
$u1->sharedFriend = $u2;
R::store($u1);
```

Instead of creating `friend` table and linking 2 users it added `sharedFriend_id` column to `user` table and now it looks like this:

```
id | username | sharedFriend_id
---|----------|----------------
 1 | Alice    | 2
 2 | Bob      | NULL
```

Questions:

- How can I implement self-referential N-M with RedBean PHP?
- If "self-referential N-M" is not the correct approach for the problem I want to solve then what would be the most "RedBean PHP"-ish way of making two users friends?

---

<sub>
Note: In the past I managed stuff like this manually by writing all the necessary logic myself. I would rather avoid doing that and learn how to do it properly using this framework if it is possible.
</sub>