How to use existing data source display method in class

Hello everyone.Today i will be discussing about how to use existing data source display method in class. Lets say we want  to create purchase order from sales order . As we all know that it is OOTB functionality. For instance on this form we would like to do some customize for which we need to access Sales Line Data source method “specifyVendAccount”.

To access this OOTB functionality we will follow this navigation : Sales and Marketing -> Sales Orders -> All sales orders -> Select any sales order -> Sales order action pane tab -> Purchase order and  below screen will be shown and the name of  form is "PurchCreateSalesOrder".

1) Open "PurchCreateSalesOrder" form from AOT.

2) Expand data source node. Inside it there will be Sales Line data source expand its methods. There you will find specifyVendAccount method.

3) Create a new class and add below code in it. By using this piece of code you will be able to specify vendor of your choice on PurchCreateFromSalesOrder form.