Relation between belongsTo and hasMany in cakephp 3.4.9 - cakephp-3.0

Question

I need to save user and invoice data at the same time. When I am submitting the form, the user data is saving, but the invoice table isn't. When I print the request data, I get the following:
object(Cake\ORM\Entity) {
'u_firstname' => 'John',
'u_lastname' => 'den',
'u_email' => 'john#man.com',
'u_phone' => '123',
'password' => '123',
'membership_id' => (int) 1,
'Invoices' => [
'inv_membership_name' => 'basic1',
'inv_membership_cost' => '55',
'inv_purchase_date' => '2017-07-11'
],
'id' => (int) 19,
'[new]' => false,
'[accessible]' => [
'*' => true
],
'[dirty]' => [],
'[original]' => [],
'[virtual]' => [],
'[errors]' => [],
'[invalid]' => [],
'[repository]' => 'Users'
}
I am not able to save the Invoice part. I define InvoicesTable.php
public function initialize(array $config)
{
parent::initialize($config);
$this->setTable('invoices');
$this->setDisplayField('id');
$this->setPrimaryKey('id');
$this->belongsTo('Users', [
'foreignKey' => 'user_id',
'joinType' => 'INNER'
]);
}
and UsersTable like this:
$this->hasMany('Invoices', [
'foreignKey' => 'user_id',
'joinType' => 'INNER'
]);
I use the following code to save data:
$user = $this->Users->newEntity();
if ($this->request->is('post')) {
$user = $this->Users->patchEntity($user, $this->request->data(), [
'associated' => [
'Invoices'
]
]);
if ($this->Users->save($user)) {
$this->Flash->success(__('The user has been saved.'));
}else{
$this->Flash->error(__('The user could not be saved. Please, try again.'));
}
}
Please suggest what I'm missing. Or how I should debug.

Answer 1

When you print request data invoices array should be something like this:
object(Cake\ORM\Entity) {
'invoices' => [
[0] => Array
(
['inv_membership_name'] => 'basic1',
['inv_membership_cost'] => '55',
['inv_purchase_date'] => '2017-07-11'
),
[1] => array('...') // if you have multiple records
],
For that change input name to something like this in your form:
invoices[]['inv_membership_name']
invoices[]['inv_membership_cost']
invoices[]['inv_purchase_date']
See here Saving HasMany Associations in CakePhp3.

Answer 2

You are close to the solution but you have the naming conventions wrong in the form. The correct name would be invoices.0.inv_membership_name
invoices.1.inv_membership_name etc. I included the creating inputs for associated data link from the cookbook.
echo $this->Form->control('invoices.0.inv_membership_name');
https://book.cakephp.org/3.0/en/views/helpers/form.html#creating-inputs-for-associated-data