class TestDto
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public List<string> Candidates { get; set; }
    }

    class TestModel
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public List<CandidateModel> Candidates { get; set; }
    }
    class CandidateModel
    {
        public DateTime StartTime { get; set; }
        public string Candidate { get; set; }
    }

class Program
    {
        static void Main(string[] args)
        {
            var testModel = new TestModel()
            {
                Name = "Frankie",
                Age = 22,
                Candidates = new List<CandidateModel>()
                {
                    new CandidateModel(){StartTime = new DateTime(2018, 10, 9, 10, 0, 0), Candidate = "贝贝"},
                    new CandidateModel(){StartTime = new DateTime(2018, 10, 22, 10, 0, 0), Candidate = "asan"},
                    new CandidateModel(){StartTime = new DateTime(2018, 10, 10, 10, 0, 0), Candidate = "pangzi"}
                }
            };
            // DataTime.Now : {2018/10/21 21:51:12}
            testModel.Candidates = testModel.Candidates.Where(_ => _.StartTime < DateTime.Now).ToList();

            Mapper.Initialize(_ => _.CreateMap<TestModel, TestDto>()
                .ForMember(s => s.Candidates,
                    d => d.MapFrom(x => x.Candidates.Select(y => y.Candidate))));

            var testDto = Mapper.Map<TestDto>(testModel);
        }
    }