I have a struct as below. After storing it I've found (to my horror) that all the field names have been converted to a lowercase version. 

type Order struct

{     TransactionID string     InvoiceID int     ID string } { "_id" : "efaa0eab-1200-439d-a9bc-5783e6574aaf",  "transactionid" : "sample transaction ID", "invoiceid" : NumberLong(1), "id" : "efaa0eab-1200-439d-a9bc-5783e6574aaf"}