I have two schemas. One is an employee one, one is an employer one. In the Employer, I have a field employee.id which will be an array of ID's from the employee schema. I select a new field and set it to id from Employee now I'd like to populate the array, but with unique values. So for example Employer with an array of ids like [200,1,749] but not have those values used again in another Employer object. so if employee ID was used for Employer 1 then that ID cannot be used in another employers employee array. Is there a way to do this so the values in the Employee ID array are unique and not repeated?