使用AutoMapper将对象属性映射为字典时遇未映射成员错误

需求是将对象的每个属性转换为字典的键值对（如Book对象的Id和Name属性对应字典的id、name键），但运行代码时触发以下错误：

Unmapped members were found. Review the types and members below.
Add a custom mapping expression, ignore, add a custom resolver, or modify the source/destination type
For no matching constructor, add a no-arg ctor, add optional arguments, or map all of the constructor parameters
=======================================================================================================================================================================================================================================================================
Book -> Dictionary`2 (Destination member list)
Book -> System.Collections.Generic.Dictionary`2[[System.String, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.String, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]] (Destination member list)

Unmapped properties:
Keys
Values
Item

用户的实现代码：

using AutoMapper;

var book = new Book()
{
    Id = 1,
    Name = "A"
};

IMapper mapper = new Mapper(new MapperConfiguration(
    config => config.CreateMap<Book, Dictionary<string, string>>()
        .ConstructUsing((source, dest) => new Dictionary<string, string>()
        {
            { "id", source.Id.ToString() },
            {"name", source.Name}
        })));

mapper.ConfigurationProvider.AssertConfigurationIsValid();

var bookData = new Dictionary<string, string>();

mapper.Map(book, bookData);

public class Book
{
    public int Id { get; set; }

    public string Name { get; set; }
}

错误原因 #

AutoMapper在执行AssertConfigurationIsValid()时，会检查目标类型（Dictionary<string,string>）的所有公共成员（Keys、Values、Item），但源类型Book没有对应的属性，因此触发未映射成员的验证错误。

解决方案 #

方案1：忽略未映射的成员 #

在映射配置中添加.ForAllOtherMembers(opt => opt.Ignore())，告诉AutoMapper忽略所有未明确映射的成员：

IMapper mapper = new Mapper(new MapperConfiguration(
    config => config.CreateMap<Book, Dictionary<string, string>>()
        .ConstructUsing((source, dest) => new Dictionary<string, string>()
        {
            { "id", source.Id.ToString() },
            {"name", source.Name}
        })
        .ForAllOtherMembers(opt => opt.Ignore())));

方案2：使用ConvertUsing定义完整转换逻辑 #

ConvertUsing可以直接定义从源对象到目标字典的转换规则，AutoMapper会跳过成员映射验证，完全遵循你定义的逻辑：

IMapper mapper = new Mapper(new MapperConfiguration(
    config => config.CreateMap<Book, Dictionary<string, string>>()
        .ConvertUsing(source => new Dictionary<string, string>()
        {
            { "id", source.Id.ToString() },
            {"name", source.Name}
        })));

同时可以简化字典的创建方式，直接通过mapper.Map生成目标字典，无需提前实例化：

var bookData = mapper.Map<Dictionary<string, string>>(book);

内容的提问来源于stack exchange，提问作者Thiago