如何简便创建含已有类全部属性及额外字段的匿名类型？

嘿，这个问题我太有共鸣了！每次写LINQ的Select都要把POCO的所有属性列一遍，再加个UUID，真的挺繁琐的。给你几个更简洁的实现思路，不管用C#还是VB都能搞定：

如果你的Person类是可以修改的，直接给它加一个Uuid属性就一劳永逸了——这样返回的时候直接用Person对象列表就行，不用额外创建匿名类型：

C# 示例 #

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    // 新增UUID属性
    public Guid Uuid { get; set; }
}

// 查询时直接赋值UUID
var people = _dbContext.People
    .Select(p => new Person
    {
        Name = p.Name,
        Age = p.Age,
        Uuid = Guid.NewGuid()
    })
    .ToList();

VB 示例 #

Public Class Person
    Public Property Name As String
    Public Property Age As Integer
    ' 新增UUID属性
    Public Property Uuid As Guid
End Class

' 查询时赋值UUID
Dim people = _dbContext.People _
    .Select(Function(p) New Person With {
        .Name = p.Name,
        .Age = p.Age,
        .Uuid = Guid.NewGuid()
    }) _
    .ToList()

如果原Person类是不能动的（比如来自第三方库），用AutoMapper可以避免重复写Select的冗余代码。只需要配置一次映射规则，之后就能一键转换：

C# 示例 #

先安装AutoMapper NuGet包，然后定义DTO和映射：

// 定义带UUID的DTO类
public class PersonWithUuid
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Guid Uuid { get; set; }
}

// 配置映射规则：把Person的属性映射到PersonWithUuid，同时生成UUID
var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<Person, PersonWithUuid>()
       .ForMember(dest => dest.Uuid, opt => opt.MapFrom(_ => Guid.NewGuid()));
});

IMapper mapper = config.CreateMapper();

// 查询时直接映射，不用手动写每个属性
var people = _dbContext.People
    .ProjectTo<PersonWithUuid>(mapper.ConfigurationProvider)
    .ToList();

VB 示例 #

' 定义带UUID的DTO类
Public Class PersonWithUuid
    Public Property Name As String
    Public Property Age As Integer
    Public Property Uuid As Guid
End Class

' 配置映射规则
Dim config = New MapperConfiguration(Sub(cfg)
    cfg.CreateMap(Of Person, PersonWithUuid)() _
       .ForMember(Function(dest) dest.Uuid, Sub(opt) opt.MapFrom(Function(_) Guid.NewGuid()))
End Sub)

Dim mapper As IMapper = config.CreateMapper()

' 查询时一键映射
Dim people = _dbContext.People _
    .ProjectTo(Of PersonWithUuid)(mapper.ConfigurationProvider) _
    .ToList()

如果不想额外定义DTO类，也可以在JSON序列化阶段动态插入UUID字段，比如用Newtonsoft.Json的JObject来处理：

C# 示例 #

using Newtonsoft.Json.Linq;

// 先获取原Person对象，再给每个对象动态添加UUID字段
var people = _dbContext.People
    .Select(p => new { Person = p, Uuid = Guid.NewGuid() })
    .Select(item => 
    {
        var jObj = JObject.FromObject(item.Person);
        jObj.Add("Uuid", item.Uuid);
        return jObj;
    })
    .ToList();

// 直接序列化这个JObject列表即可
string json = Newtonsoft.Json.JsonConvert.SerializeObject(people);

VB 示例 #

Imports Newtonsoft.Json.Linq

' 动态添加UUID字段
Dim people = _dbContext.People _
    .Select(Function(p) New With {.Person = p, .Uuid = Guid.NewGuid()}) _
    .Select(Function(item)
        Dim jObj = JObject.FromObject(item.Person)
        jObj.Add("Uuid", item.Uuid)
        Return jObj
    End Function) _
    .ToList()

' 序列化
Dim json = Newtonsoft.Json.JsonConvert.SerializeObject(people)

内容的提问来源于stack exchange，提问作者ryan