How to join invoiceitem and invoice base objects

[Casey]

Greetings,

So, the documentation around the Aqua API recommends the following:

"When extracting data from Zuora with AQuA, Zuora recommends that you avoid querying fields from the joined objects of a data source. You should restrict your query to only include the fields from the base object of the data source."

See:

https://knowledgecenter.zuora.com/Central_Platform/API/AB_Aggregate_Query_API/Bulk_data__extraction_...

However, after querying the invoiceitem object I don't see any field that permits a join to a specific invoice.  Can anyone tell me what objects and fields are required to perform such a join?