CakePHP 3.7.7 saving multiple entities efficiently - cakephp

Question

CakePHP 3.7.7
I have a series of checkboxes. Name attributes are: emailFrequency_daily, emailFrequency_weekly and emailFrequency_monthly.
I want to save the ones that have been checked and need to save these alongside some other data I have stored in the session: session data o_id and u_id are the same every time a row is inserted. A frequency field in the database matches the appropriate checkbox and is different every time as per the list above.
So I have tried following https://book.cakephp.org/3.0/en/orm/saving-data.html#saving-multiple-entities
In my Controller I have the following
$TblAlertFrequency = TableRegistry::get('TblAlertFrequency');
$frequencies = [];
// 'daily' emails enabled
if ($this->request->getData('emailFrequency_daily')) {
$frequencies[] = [
'u_id' => $this->_UserModel->getUserId(),
'o_id' => $this->_UserModel->getOrgId(),
'frequency' => 'daily'
];
}
// 'weekly' emails enabled
if ($this->request->getData('emailFrequency_weekly')) {
$frequencies[] = [
'u_id' => $this->_UserModel->getUserId(),
'o_id' => $this->_UserModel->getOrgId(),
'frequency' => 'weekly'
];
}
// 'monthly' emails enabled
if ($this->request->getData('emailFrequency_monthly')) {
$frequencies[] = [
'u_id' => $this->_UserModel->getUserId(),
'o_id' => $this->_UserModel->getOrgId(),
'frequency' => 'monthly'
];
}
if (!empty($frequencies)) {
$entities = $TblAlertFrequency->newEntities($frequencies);
$TblAlertFrequency->saveMany($entities);
}
It's giving a 500 Internal Server error with the message:
Error: Cannot insert row, some of the primary key values are missing. Got (, ), expecting (o_id, u_id)
Why is this, given I'm passing it those values (o_id and u_id)?
The table structure is as follows:
mysql> describe tbl_alert_frequency;
+-----------+------------------------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------------------------------------+------+-----+---------+-------+
| u_id | mediumint(8) unsigned | NO | PRI | NULL | |
| o_id | smallint(5) unsigned | NO | PRI | NULL | |
| frequency | enum('never','daily','weekly','monthly') | NO | | weekly | |
+-----------+------------------------------------------+------+-----+---------+-------+
The only thing I'm not passing it is the id because that's AUTO_INCREMENT and therefore written by MySQL on inserting a new row.
The code I've written here isn't DRY because it repeats:
'u_id' => $this->_UserModel->getUserId(),
'o_id' => $this->_UserModel->getOrgId(),
But if I remove those it won't save them, and they are needed on every row.
Surely there is an easier and more efficient way to write this?
I also looked at How to save multiple records in cakephp 3 but that seems outdated and didn't work for me.