How to know if Lookup column is deferred or not using REST API

Question

I'm trying to use the REST APi to get data from a sharepoint list. I first get the information about the columns: _api/Web/List<guid'some-id')/Fields. Then with this information I query the data _api/Web/Lists(guide'some-id')/Items?$top=5000. If any of the columns are of type Lookup or LookupMulti then I append the &$select=<column_name>/Title and &$expand=<column_name> to the url.

The issue is that only deferred Lookup columns can actually be returned by the REST API. If they are not then I get an error.

How can I figure out which Lookup columns are deferred or not? That way I won't try to expand those and my request won't fail.

Answer 1

Once a query is submitted, then review the returned record and each lookup field that has a '__deferred' element is available for expansion through the &$expand=Folder term as an example.

If there are no associated records within the deferred field it will still show the '__deferred' element, which indicates that there is no child record present for this items field.