In this tutorial, you will learn to copy custom data from a quote object to an order object using the Magento/Framework/DataObject/Copy class.
Step 1: Define your attributes
The following code defines a simple extension attribute named demo for the Cart and Order objects.
extension_attributes.xml
Step 2: Configure the fieldset
The following code adds the demo field to the sales_convert_quote fieldset with the to_order aspect.
The code snippet in the next step uses the name of the fieldset and aspect to specify which fields to copy.
fieldset.xml
Step 3: Copy the fieldset
The following code snippets highlight the code pieces needed to copy a fieldset using the \Magento\Framework\DataObject\Copy class.
In the code, an instance of the Copy class is obtained from the constructor using dependency injection.
The copyFieldsetToTarget function call with the $quote and $order parameters copies the fieldset for the two objects..