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投影投影接口定义

news 2026/6/25 18:53:07

投影接口定义

IProjection接口很简单
只有TryConvert一个方法
相同类型对象的转化,返回是否成功以及转化后的结果
约定不符合规则就不转化
一般情况下转化成功的结果会和源对象不同
当然经过多次投影后也可能会和源对象相同了

public interface IProjection<T> { bool TryConvert(T source, out T result); }

2. 三种投影方式

2.1 使用前缀投影来演示

前缀投影就是把成员前面加个前缀来映射
sourceMembers模拟对User的反射
通过Projection.Prefix("User")创建一个前缀投影
如果没有User前缀,就增加User
如果有User前缀就不处理

public record User(int Id, string UserName); public record UserDTO(int UserId, string UserName); var sourceMembers = new Dictionary<string, Func<User, object>>() { [nameof(User.Id)] = obj => obj.Id, [nameof(User.UserName)] = obj => obj.UserName }; var projection = Projection.Prefix("User");

2.2 Filter投影的Case

2.2.1 csharp代码

IDictionary<string, Func<User, object>> result = projection.Filter(sourceMembers); Assert.Single(result); Assert.True(result.ContainsKey(nameof(UserDTO.UserId)));

2.2.2 sql表示

SELECT Id AS UserId FROM User

2.2.3 影像表示

User

Filter

UserName

UserId

2.3 Through投影的Case

2.3.1 csharp代码

IDictionary<string, Func<User, object>> result = projection.Through(sourceMembers); Assert.Equal(sourceMembers.Count, result.Count); Assert.True(result.ContainsKey(nameof(UserDTO.UserId))); Assert.True(result.ContainsKey(nameof(UserDTO.UserName)));

2.3.2 sql表示

SELECT Id AS UserId,UserName FROM User

2.3.3 影像表示

User

Through

UserName

UserId

UserName

2.4 Cross投影的Case

PocoEmit.Mapper重构用的就是Cross投影

2.4.1 csharp代码

IDictionary<string, Func<User, object>> result = projection.Cross(sourceMembers); Assert.Equal(3, result.Count); Assert.True(result.ContainsKey(nameof(User.Id))); Assert.True(result.ContainsKey(nameof(UserDTO.UserId))); Assert.True(result.ContainsKey(nameof(UserDTO.UserName)));

2.4.2 sql表示

SELECT Id,UserName,Id AS UserId FROM User

2.4.3 影像表示

User

Cross

UserName

UserId

3. 投影支持"横向"扩展

这里说的"横向"就是投影并联
把多个投影组合成多分支的映射规则
通过FirstReturn或ToFirstReturn方法实现

3.1 "横向"扩展的Case

// 包含User或U前缀就去掉前缀 var user = Projection.RemovePrefix("User"); var u = Projection.RemovePrefix("U"); var projection = Projection.FirstReturn(user, u); [Theory] [InlineData("UserId", "Id")] [InlineData("UId", "Id")] [InlineData("UUserName", "UserName")] [InlineData("UserUName", "UName")] public void TryConvert(string source, string expected) { projection.TryConvert(source, out var result); Assert.Equal(expected, result); }

3.2 影像表示"横向"扩展

RemoveUser和RemoveU两个并联的投影
并联投影按照顺序依次尝试
直到有一个投影成功了就返回结果

expected

source

RemoveUser

RemoveU

RemoveUser

UserId

UId

UUserName

UserUName

UserName

UName

二、投影在PocoEmit.Mapper中的应用

1. AddPrefix

1.1 AddPrefix的Case

IMapper mapper = Mapper.Create(); mapper.ConfigureMap<AutoUserDTO, User>() .Source .AddPrefix("User"); var source = new AutoUserDTO { UserId = "222", UserName = "Jxj2" }; var converter = mapper.GetConverter<AutoUserDTO, User>(); var result = converter.Convert(source); Assert.NotNull(result); Assert.Equal(source.UserId, result.Id.ToString()); Assert.Equal(source.UserName, result.UserName);

1.2 AddPrefix使用的是去除前缀投影(RemovePrefix)

AddPrefix("User")会调用Projection.RemovePrefix("User")来创建一个去除前缀投影
AutoUserDTO两个成员分别是UserId和UserName
User两个成员分别是Id和UserName
对AutoUserDTO投影的效果相当于sql: SELECT UserId,UserName,UserId AS Id FROM AutoUserDTO
通过这个投影,两边的成员名就能完美匹配上了