I know you could do Coll.findOne({ email_1: 'abc@somedomain.com' })
to look up abc@somedomain.com against the field email_1 in collection Coll. However, what if there were several email fields (email_1, email_2, email_3, etc.) and I needed to look up a given email against all those fields?
I could reiterate Coll.findOne({ email_1: 'abc@somedomain.com' })
for each field in my collection but that obviously isn't most optimal.