In the business domain you can model unique fields for a Business Domain class.
In the service model this information can be used to declare getBy services.
Via codecompletion the available names of the unique rules ("unique" keyword) should be presented to the developer.
Class Person [
"The combination of first- and last name of a person must be unique"
unique fullName [firstName lastName]
should result in a service method like this:
public Person getByFullName(String firstName, String lastName);