使用AutoMapper进行属性展开到字符串的过程中，需要在映射配置中为目标属性指定映射方式，例如源属性到字符串的映射方式可以使用“.ToString()”。示例代码如下：

public class SourceObject
{
    public int Id { get; set; }
    public DateTime Date { get; set; }
}

public class DestinationObject
{
    public string Id { get; set; }
    public string Date { get; set; }
}

// 映射配置
var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap()
        .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.Id.ToString()))
        .ForMember(dest => dest.Date, opt => opt.MapFrom(src => src.Date.ToString()));
});

// 使用Mapper执行映射
var source = new SourceObject { Id = 1, Date = new DateTime(2020, 1, 1) };
var mapper = config.CreateMapper();
var destination = mapper.Map(source);