As a general comment: please put more effort into explaining what it is that you are trying/wanting to do - with some example detail. I would rather spend time trying to figure out an answer than trying to figure out what the question
My best guess is that you are wanting to save a new object, but wanting to check whether that new object would duplicate one already persisted in the database? Is that correct?
If so: is the non-duplication enforced in the database (via uniqueness constraints) or are you wanting to enforce the uniqueness in the domain model without it being constrained in the database? Is the uniqueness defined by all the properties on the
object or just a subset (e.g. Name, Date)?