Avoid POST Duplicates in a .NET API
Use LINQ to check if there is a duplicate in the DB before posting the data. This will allow you to block duplicated data before coming in, if your business rules do not allow them.
Some examples could be:
A product that a worker should not repeat because of an inventory set up/business rule, a transaction that can´t have duplicates, or just to double check that someone is already a customer.