Saving HasMany Associations Data in CakePHP 3.x - php

Question

I am having two tables. My primary table is Students. And my secondary table is Exams. I am trying to save both the tables using hasMany and belongsToMany Association. But It is saving data in Student table only, not in Exams. Can any one help me to resolve this problem.
Students Model :
class StudentsTable extends Table {
public function initialize(array $config) {
$this->addBehavior('Timestamp');
parent::initialize($config);
$this->table('students');
$this->primaryKey(['id']);
$this->hasMany('Exams', [
'className' => 'Exams',
'foreignKey' => 'student_id',
'dependent'=>'true',
'cascadeCallbacks'=>'true']);
}
}
Exams Model :
class ExamsTable extends Table {
public function initialize(array $config) {
parent::initialize($config);
$this->table('exams');
$this->primaryKey(['id']);
$this->belongsToMany('Students',[
'className'=>'Students',
'foreignKey' => 'subject_id',
'dependent'=>'true',
'cascadeCallbacks'=>'true']);
}
}
My school.ctp :
echo $this->Form->create();
echo $this->Form->input('name');
echo $this->Form->input('exams.subject', array(
'required'=>false,
'multiple' => 'checkbox',
'options' => array(
0 => 'Tamil',
1 => 'English',
2 => 'Maths')));
echo $this->Form->button(__('Save'));
echo $this->Form->end();
In my controller:
public function school() {
$this->loadModel('Students');
$this->loadModel('Exams');
$student = $this->Students->newEntity();
if ($this->request->is('post')) {
$this->request->data['exams']['subject'] =
implode(',',$this->request->data['exams']['subject']);
$student = $this->Students->patchEntity(
$student, $this->request->data, ['associated' => ['Exams']]
);
if ($this->Students->save($student)) {
$this->Flash->success(__('The user has been saved.'));
} else {
$this->Flash->error(__('Unable to add the user.'));
}
}
}

Answer 1

Patching BelongsToMany Associations
You need to make sure you are able to set exams. Set accessibleFields to allow you to patch associated data
$student = $this->Students->patchEntity(
$student, $this->request->data, [
'associated' => ['Exams'],
'accessibleFields' => ['exams' => true]
]
);
You can also do this with the $_accessible property in the entity.

Answer 2

I've never done hasMany to belongsToMany because i don't think it works that way (I mean no harm in my words.) But I'll try to explain. Your relationships should be both belongsToMany because exams will have many students and students will have many exams. So basically they're the same either way. What you need is another table to connect them which will be called students_exams or exams_students (i think its exams_students because E comes before S) because in cake if you name everything properly most of it happens automatically.
Assuming you know how patchEntity works, creating your $this->request->data properly will patch it automatically and save it in the correct table when you save it. If you have any more questions feel free to ask more. :)