可通过使用 AutoMapper 的“IgnoreUnmapped”选项来防止此问题发生。示例如下：

// 定义源类 public class SourceClass { public int Id { get; set; } public List Items { get; set; } }

public class SourceItemClass { public int Id { get; set; } public string Name { get; set; } }

// 定义目标类 public class DestinationClass { public int Id { get; set; } public List Items { get; set; } }

public class DestinationItemClass { public int Id { get; set; } public string Name { get; set; } }

// 使用 AutoMapper 进行映射 var config = new MapperConfiguration(cfg => { cfg.CreateMap() .ForMember(dest => dest.Items, opt => opt.MapFrom(src => src.Items)) .ForAllOtherMembers(opt => opt.Ignore()); // 忽略未映射的属性 });

var mapper = config.CreateMapper();

var source = new SourceClass { Id = 1, Items = new List { new SourceItemClass { Id = 1, Name = "Item 1" }, new SourceItemClass { Id = 2, Name = "Item 2" }, } };

var destination = new DestinationClass { Id = 999, Items = new List { // 已填充的目标类嵌套列表元素 new DestinationItemClass { Id = 100, Name = "Existing Item 1" }, new DestinationItemClass { Id = 200, Name = "Existing Item 2" }, } };

mapper.Map(source, destination);

// 验证目标类嵌套列表元素的值是否被保留 Console.WriteLine(destination.Items.Count); // 2

foreach (var item in destination.Items) { Console.WriteLine($"Id:{item.Id} Name:{item.Name}"); // 输出结果： // Id:100 Name:Existing Item 1 // Id:200 Name:Existing Item 2 }