CakePHP 3 : Cannot get JSON data from controller - php

Question

I'm trying to return a query made in a controller to the view file so I can use that data in my form. But I am unable to successfully return the data without errors. I know the function is working because it returns the right data but has an error.
Here is my CustomersController fill function which is running the sql query.
public function fill(){
$layout = 'ajax';
$this->autoRender = false;
if ($this->request->is('post')) {
$id = $this->request->data['id'];
$query = $this->Customers->find()
->where([
'id' => $id
])->first();
echo json_encode($query);
}
}
and here is my blah.ctp which is the view file.
<?php use Cake\Routing\Router; ?>
<?= $this->Form->create(Null, ['type' => 'POST']) ?>
<?php
echo $this->Form->input('customer_id', ['options' => $customers, 'empty' => true,'id'=>'customers']);
?>
<?= $this->Form->end() ?>
<script>
document.getElementById('customers').addEventListener('change',function(){
var id = this.value;
var csrfToken = $('[name=_csrfToken]').val();
$.ajax({
type: "POST",
url: '<?php echo Router::url(array("controller" => "Customers", "action" => "fill")); ?>',
data: {'id' : id},
beforeSend: function(xhr){
xhr.setRequestHeader('X-CSRF-Token', csrfToken);
},
success: function(data){
alert(data);
}
});
});
</script>
Currently this is what happens when I select a customer in my drop down box which triggers the script in the view.
As you can see it returns the array of data I need but also has the error cannot emit headers. I have tried solving this error following other questions on stack overflow but can't solve it.
I've tried using $this->set instead of echo json_encode but it always returns nothing. I'm not sure what other way to do this.

Answer 1

First of all, If you're selecting a single record by a unique ID, you can call
->get($id) on the table object directly, instead of building a query chain with ->find().
CakePHP 3.x should automatically handle converting your view to JSON by using the RequestHandlerComponent. Typically, you must enable it if your scaffolding or installation didn't.
1) Enable request handler component. (If not already enabled) https://book.cakephp.org/3.0/en/controllers/components/request-handling.html
2) Remove the echo json_encode($query) line; you should not echo anything as this will break the request/response cycle. This is the cause of your error.
Instead, you should serialize your data to the view. Assuming you have the fetched data in $data: $this->set(compact('data')). Then, make sure you add $this->set('_serialize', ['data']) (again, assuming the data is stored in variable name 'data').
3) Reference this doc for information on how you can request the json. You can use a file extension (.json, .xml).
Also, make sure you add the 'Accept: application/json' header to your request.(https://book.cakephp.org/3.0/en/development/routing.html#Cake\Routing\Router::extensions).
I apologize for the fuzzy response. There are many ways to achieve this with CakePHP3. Please see this doc page for more information: https://book.cakephp.org/3.0/en/views/json-and-xml-views.html