cakephp: how do you load a behavior from a plugin? - cakephp

Question

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I used cake bake to make a new plugin and behavior (using --plugin) and it worked. Not sure what I missed.
I'm trying to load the behavior of a plugin. I'm trying to do this with a plugin I wrote for my own use, but I get the same problem when trying to load someone else's.
For example loading https://github.com/Xety/Cake3-Upload
I know you should normally use composer, but this is the way I would load my own plugin.
copy the plugin to \app\plugins\Cake3Upload
load the plugin in bootstrap.php using
Plugin::load('Cake3Upload', ['autoload' => true]);
access the behavior in my model's MyModelTable.php initialize function
$this->addBehavior('Cake3Upload.Upload');
I then get the following error:
Missing Behavior
Cake3Upload.UploadBehavior could not be found.
Make sure your plugin was loaded from config\bootstrap.php and
Composer is able to autoload its classes, see Loading a plugin and
Plugins - autoloading plugin classes
Error: Create the class UploadBehavior below in file:
\app\plugins\Cake3Upload\src\Model\Behavior\UploadBehavior.php
use Cake\ORM\Behavior;
class UploadBehavior extends Behavior
{
}

Answer 1

And what about namespaces ? If u wont use composer u must build the same files tree.
I think it's just about the uploadBehavior have this namespace:
namespace Xety\Cake3Upload\Model\Behavior;
then u only have to follow the plugin doc:
Plugin::load('Xety/Cake3Upload');
and
$this->addBehavior('Xety/Cake3Upload.Upload');
Add 'Xety/' maybe