Contacts many_to_many relationship with Users - how to use?

Question

If you navigate to Admin -> Studio -> Contacts -> Relationships, you will see that Contacts has a many-to-many relationship with Users.

I cannot access a contact's users via the API. I've tried `Contacts/:id/link/users`, `Contacts/:id/collection/users`, `Contacts/:id/link/contacts_users`, and `Contacts/:id/link/contacts_users`. How exactly can we access this relationship via the API?

Context: we are using SugarCRM as an API for a custom frontend, and we would like to leverage the many-to-many relationship between contacts and users to set up restricted visibility for assigned users. I'm aware that SugarCRM has a default assigned_user field, but we need to assign more than one user to contacts.

Gregory Kenenitz · Accepted Answer

The link name is user_sync (see modules/Contacts/vardefs.php), so ' Contacts/:id/link/user_sync' would return a contact's users. Coming from users, the link name is contacts_sync (see modules/Users/vardefs.php). But the contacts_users relationship is used for contact syncing with the MS Outlook Plug-in. 
 As Jeff said, Teams and Team-Based Permissions should do what you want. Remember that for every user in Sugar, a corresponding private team is automatically created. So you can add or remove access for individual users by adding/removing their private teams.