Read AD properties in SharePoint Online

Hi,

We are using SharePoint Online. 

Requirement is to read logged in users properties (Business Unit) and categorize employees as per theBusiness Unit. 

1. Tried to read AD properties using REST services
2. But BU in AD properties is not a mandatory field therefore we are not getting value for all employees
3. Client is giving database of all employees in excel file. Client database contains 1 lakh and more records.

Please share your ideas/thoughts for better handling.

Regards,

Sudheer

Thanks & Regards, Sudheer