Get all guest & customer email id's in single collection Magento 2

Question

I am trying to list all unique email id's (guest & customers) in admin grid to restrict specific email id to place order.

For that, I got an id's from customer collection and order collection.

But I need this in the single collection.

name | email
A    | [email protected]
B    | [email protected]
C    | [email protected]

FYI:

/* \Magento\Customer\Model\CustomerFactory */
$customerCollection = $model->getCollection();
$customerCollection->getSelect()
    ->reset(\Zend_Db_Select::COLUMNS)
    ->columns(
    [
        'name' => "CONCAT(firstname, ' ', lastname)",
        'email' => 'email'
    ]
);

/* \Magento\Sales\Model\OrderFactory */
$orderModel = $this->_orderFactory->create();
$orderCollection = $orderModel->getCollection();
$orderCollection->addAttributeToFilter('customer_is_guest', ['eq' => 1]);
$orderCollection->getSelect()
    ->reset(\Zend_Db_Select::COLUMNS)
    ->columns(
        [
          'name' => "CONCAT(customer_firstname, ' ', customer_lastname)",
          'email' => 'customer_email'
        ]
    );

Even I tried with preparing a new collection \Magento\Framework\Data\Collection && \Magento\Framework\DataObject in this cases filter, page size, cur page not working.

After collecting those data need to list in admin grid.

Please suggest the possible way?

Thanks

Answer 1

First, you don't have any idea on two different type of collection join.

So far my understanding, you can follow below also as an alternative solution.

Make two collections and filter those collections using email of current quote or order email