Call to undefined method on custom collection Resource Model

Question

I have been trying to figure this out for 2 days. I created a custom collection for my module structured as follows

app/code/Morello/Customproducts/Model/CustomProducts.php

namespace Morello\Customproducts\Model;

use Magento\Framework\Model\AbstractModel;

class CustomProducts extends AbstractModel
{
    protected function _construct()
    {
        $this->_init('Morello\Customproducts\Model\ResourceModel\CustomProducts');
    }
}

app/code/Morello/Customproducts/Model/ResourceModel/CustomProducts.php

namespace Morello\Customproducts\Model\ResourceModel;

use Magento\Framework\Model\ResourceModel\Db\AbstractDb;

class CustomProducts extends AbstractDb
{
    protected function _construct()
    {
        $this->_init('customer_products', 'customproduct_id');
    }
}

app/code/Morello/Customproducts/Model/ResourceModel/CustomProducts/Collection.php

namespace Morello\Customproducts\Model\ResourceModel\CustomProducts;

use Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection;

class Collection extends AbstractCollection
{

    protected function _construct()
    {
        $this->_init('Morello\Customproducts\Model\CustomProducts', 'Morello\Customproducts\Model\ResourceModel\CustomProducts');
    }

}

In my observer I use the CustomProductsFactory and call methods on it. addFieldToSelect, addFieldToFilter, load, setData and save all work, but when I try to call the delete method to remove an entry in the table it throws a fatal error

Fatal error: Uncaught Error: Call to undefined method Morello\Customproducts\Model\ResourceModel\CustomProducts\Collection::delete() in etc...

What am I missing? The Collection class in the ResourceModel\CustomProducts folder extends the right framework class...

Any help is appreciated.

EDIT:

This is a very simplified version of my observer...

app/code/Morello/Customproducts/Observer/Backend/CustomerSaveAfter.php

namespace Morello\Customproducts\Observer\Backend;

use Magento\Framework\App\ObjectManager;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Morello\Customproducts\Model\CustomProductsFactory;

class CustomerSaveAfter implements ObserverInterface
{

    private $customProductsFactory;

    public function __construct(
        CustomProductsFactory $customProductsFactory
    )
    {
        $this->customProductsFactory = $customProductsFactory;
    }

    public function execute(Observer $observer)
    {
        $customerId = '1';
        $productsToRemoveFromCustomer = array(1, 3, 27);

        $customProductModel = $this->customProductsFactory->create();
        $customProductCollection = $customProductModel->getCollection();

        $customProductCollection
            ->addFieldToSelect('customproduct_id')
            ->addFieldToFilter(
                'customer_id',
                ['eq' => $customerId ]
            )->addFieldToFilter(
                'product_id',
                ['in' => $productsToRemoveFromCustomer ]
            )
            ->load();
            ->delete();
    }
}

Answer 1

the collection class does not have a delete method. Only the model and resource model classes do have this.

If you could further describe, what your observer should do, I could maybe provide further information

Answer 2

I solved my issue... I accepted David Verholen's answer as correct because indeed the Collection class does not have a delete() method, however I decided to post the solution to my issue so that it could be helpful to someone else.

I had to split the deletion process in 2 parts in the Observer::execute() method as follows:

public function execute(Observer $observer)
{
    $customerId = '1';
    $productsToRemoveFromCustomer = array(1, 3, 27);
    $customProductDeleteCollection = $this->customProductsFactory->create();

    $idToRemove = $customProductDeleteCollection
                      ->getCollection() // USE THE COLLECTION 
                      ->addFieldToSelect('customproduct_id') // TO SELECT PRIMARY ID
                      ->addFieldToFilter( // USE CONDITIONS
                          'customer_id',
                          ['eq' => $customerId ]
                      )->addFieldToFilter(
                          'product_id',
                          ['in' => $productsToRemoveFromCustomer ]
                      )
                      ->load() // LOAD QUERY
                      ->getItems(); // GET THE RETURNED ITEMS

    foreach ($idToRemove as $item){
        $customProductDeleteCollection  // GET THE MODEL AGAIN
        ->load($item->getData('customproduct_id')) // LOAD THE ITEM'S PRIMARY ID
        ->delete(); // ERASE IT FROM THE FACE OF THE EARTH...
    }
}