Linking Purch. Inv. Line to G/L Entry

I am trying to build a report that pulls the Purch. Inv. Line description for a particular line of an invoice with other details from the corresponding G/L entry.  I cannot find a link, direct or indirect, between these tables other than a document no.  I could use the document number and amount as filters, which would work most of the time.  However, it isn't error-proof since the same amount could occur multiple times in one invoice.  Has anyone found a way around this problem? Thanks in advance.