You misinterpreted what they said. You had said you didn't know what hashes might be good for, and i provided an answer. You were using them inappropriately: as a unique key, rather than an indexing key, which are two different things. Since a hash is not guaranteed to be unique, you obviously should not use it for such a purpose.
That said, you need to reconsider what you can use as a unique key, if that is what you need. This is a question for you to decide. I don't know your application, and so can't really help.