Strongloop Loopback Native SQL - mysql

Question

I have the following situation in a loopback application:
I have a 'Person' class that extends from built in 'User'
I have students ('Person' class with Role 'student')
I have teachers ('Person' class with Role 'teacher')
I have classgroups (ClassGroup class related to Person class with hasManyAndBelongsTo)
Students and Teachers are added to classgroups in the same way. Teachers can have multiple classgroups, students not. If I want to see all the students that are in the same classgroups, as a teacher, I use a remote method on Person. In that method I use the following SQL (21 is the id of the teacher):
SELECT * FROM `Person`
JOIN `ClassGroupPerson`
ON `Person`.`id` = `ClassGroupPerson`.`personId`
JOIN `RoleMapping`
ON `RoleMapping`.`principalType` = "USER"
AND `RoleMapping`.`principalId` = `Person`.`id`
JOIN `Role`
ON `Role`.`name` = "student"
AND `Role`.`id` = `RoleMapping`.`roleId`
WHERE
`ClassGroupPerson`.`classGroupId` IN (
SELECT `classGroupId`
FROM `ClassGroupPerson`
WHERE `personId` = 21
)
In the documentation, it says, that using native Mysql is discouraged (http://docs.strongloop.com/display/public/LB/Executing+native+SQL).
How would I achieve the same result in 'Loopback-style'. I've tried with filters, include, hasManyTrough, ... -stuff but I'm not able to achieve the same result?
Extra question: the result from this are JSON objects, how can I convert those easily into Person objects?
EDIT
With the following code in my remote method, I'm getting close:
Person.find({
include: {
relation: 'classgroups',
scope: {
include: {
relation: 'people'
}
}
},
where: {
id: id
}
}, function(err, people){
cb(err, people);
});
I have as a result: my teacher, with his classgroups included, and with each classgroup, I have the connected persons (teachers and students). The problem that remains, is that the teacher is also included in the classrooms, so I should be able to filter the result by Role = 'student', and I don't see how to do that?