// Class
public class Department
{
    public long Id { get; set; }

    public string DepartmentName { get; set; }
}

// IDepartment Manager
public interface IDepartmentManager
{
    Task<Department> CreateDepartment(Department entity);
    Task Update(Department entity);
    Task Delete(long id);
    Task<IEnumerable<Department>> GetAll();
}

// Department Manager
private readonly IRepository<Department, long> _departmentRepo;
public DepartmentManager(IRepository<Department, long> departmentRepo)
{
    _departmentRepo = departmentRepo
}