retreiving fields from asscoaied models cakephp3 - cakephp

Question

I dont understand from the docs why I cant retrieve selected fields from associated data.
I have 2 many to many relationships in the contain which displays everything fine.
$query3 = $this->find()
->contain(['Subjects','AvailabilityForStudents'])
->select([
'Students.id','Students.first_name','Students.last_name','Students.address_billing','Students.address_lat','Students.address_long',
'Students.class_year','Students.address_street','Students.address_suburb','Students.address_postcode','Students.address_state'])
->where(['Students.id IN' => $stids])
->order(['Students.first_name' => 'ASC'])
->hydrate(true);
My Question is that instead of getting every field from the contained models why cant I select fields from the contained model as below? I am not selecting based on a criteria like in matching clause?
$query3 = $this->find()
->contain(['Subjects','AvailabilityForStudents'])
->select(['Subjects.name','Subjects.id','AvailabilityForStudents.id',
'Students.id','Students.first_name','Students.last_name','Students.address_billing','Students.address_lat','Students.address_long',
'Students.class_year','Students.address_street','Students.address_suburb','Students.address_postcode','Students.address_state'])
->where(['Students.id IN' => $stids])
->order(['Students.first_name' => 'ASC'])
->hydrate(true);
//student model
$this->hasMany('AvailabilityForStudents', [
'className' => 'AvailabilityForStudents',
'foreignKey' => 'student_id',
'dependent' => false,
]);
$this->belongsToMany('Subjects', [
'foreignKey' => 'student_id',
'targetForeignKey' => 'subject_id',
'joinTable' => 'subjects_students'
]);
//update contain
$query3 = $this->find()
->contain([
'Subjects'=>['fields'=>['name','id','SubjectsStudents.student_id']],
'AvailabilityForStudents' ])
// ->contain(['Subjects','AvailabilityForStudents'])
->where(['Students.student_unallocated' => 1,'Students.student_inactive' => 0])
->order(['Students.first_name' => 'ASC'])
->hydrate(true);
https://book.cakephp.org/3.0/en/orm/retrieving-data-and-resultsets.html

Answer 1

You are doing right.
You can try this also,
$query3 = $this->find()
->contain([
'Subjects'=>['fields'=>['name','id','SubjectsStudents.student_id']],
'AvailabilityForStudents'=>['fields'=>'id']
])
->select(['Students.id','Students.first_name','Students.last_name','Students.address_billing','Students.address_lat','Students.address_long',
'Students.class_year','Students.address_street','Students.address_suburb','Students.address_postcode','Students.address_state'])
->where(['Students.id IN' => $stids])
->order(['Students.first_name' => 'ASC'])
->hydrate(false)->toArray();