CakePHP 3.x - save not work in associate table - cakephp-3.7

Question

I have below table structure.
Mandator table
class MandatorTable extends Table
{
public function initialize(array $config)
{
$this->table('mandators');
$this->belongsToMany('Seminar', [
'foreignKey' => 'mandator_id',
'targetForeignKey' => 'seminar_id',
'joinTable' => 'mandators_seminars'
]);
}
}
Semiar table
class SeminarTable extends Table
{
public function initialize(array $config)
{
$this->table('seminars');
$this->belongsToMany('Mandator', [
'foreignKey' => 'seminar_id',
'targetForeignKey' => 'mandator_id',
'joinTable' => 'mandators_seminars'
]);
}
}
both table are belong to 'mandators_seminars' table
mandator_id, seminar_id
When I save data it's save in seminar table but not in 'mandators_seminars' table
Query
$seminartable = $this->Seminar->newEntity();
$this->request->data['mandator'][0] = 1;
$seminardata = $this->Seminar->patchEntity($seminartable, $this->request->data);
$this->Seminar->save($seminardata)
Request data
Array
(
[bookable] => test
[released] => aaa
[linkable] => bb
[name] => ccc
[internalnote] => ddd
[abstract] => ttt
[description] => ddd
[Category] => 14
[mandator] => Array
(
[0] => 1
)
[mandator_owner_id] => 1
)

Answer 1

Look you have two table Mandator and Similar as singular , but your connecting table is plural. Firstly check this. If there is still a problem check this CakePHP Through Association
As you can see your association should be like this:
$this->belongsToMany('Mandator', [
'foreignKey' => 'seminar_id',
'targetForeignKey' => 'mandator_id',
'through' => 'PluginName.MandatorsSeminars'
'joinTable' => 'mandators_seminars',
'className' => 'PluginName.Mandator'
]);
And one more tip: table should be called as plural.