How to access custom columns in a sharepoint library - graph API

Question

I am listing the children in the root of a document library with custom columns. When I make the following call with the MS graph REST API, no custom column data is returned

Answer 1

Endpoint GET https://graph.microsoft.com/beta/sites//drive/root/children returns the collection of files metadata (DriveItem resource) in the root of the drive.

The associated document library list items could be retrieved via DriveItem.listItem property including the values of the columns set on this list item (via ListItem.fields property) like this:

https://graph.microsoft.com/v1.0/sites/root/drive/root/children?$expand=listItem($expand=fields) 

Alternatively, SharePoint Library list items and column values (including custom ones) could be retrieved instead:

GET https://graph.microsoft.com/v1.0/sites/root/drive/list/items?$expand=fields

or list items along with files metadata:

GET https://graph.microsoft.com/v1.0/sites/root/drive/list/items?$expand=fields,driveItem