C# 高性能对象映射（表达式树实现）

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来源：costyuan

cnblogs.com/castyuan/p/9324088.html

前言

上篇《.NET Core高性能对象转换》简单实现了对象映射,针对数组，集合，嵌套类并没有给出实现，这一篇继续完善细节。

开源对象映射类库映射分析

1.AutoMapper

实现原理：主要通过表达式树Api 实现对象映射

优点： .net功能最全的对象映射类库。

缺点：当出现复杂类型和嵌套类型时性能直线下降，甚至不如序列化快

2.TinyMapper

实现原理：主要通过Emit 实现对象映射

优点：速度非常快。在处理复杂类型和嵌套类型性能也很好

缺点：相对AutoMapper功能上少一些，Emit的实现方案，在代码阅读和调试上相对比较麻烦，而表达式树直接观察 DebugView中生成的代码结构便可知道问题所在

3. 本文的对象映射库

针对AutoMapper 处理复杂类型和嵌套类型时性能非常差的情况，自己实现一个表达式树版的高性能方案

此篇记录下实现对象映射库的过程

构造测试类

public class TestA

{

public int Id { get; set; }

public string Name { get; set; }

public TestC TestClass { get; set; }

public IEnumerable<TestC> TestLists { get; set; }

}

public class TestB

{

public int Id { get; set; }

public string Name { get; set; }

public TestD TestClass { get; set; }

public TestD[] TestLists { get; set; }

}

public class TestC

{

public int Id { get; set; }

public string Name { get; set; }

public TestC SelfClass { get; set; }

}

public class TestD

{

public int Id { get; set; }

public string Name { get; set; }

public TestD SelfClass { get; set; }

}

1、初步实现

利用表达式树给属性赋值利用 Expresstion.New构造 var b=new B{};

private static Func<TSource, TTarget> GetMap<TSource, TTarget>()

{

var sourceType = typeof(TSource);

var targetType = typeof(TTarget);

//构造 p=>

var parameterExpression = Expression.Parameter(sourceType, "p");

//构造 p=>new TTarget{ Id=p.Id,Name=p.Name };

var memberBindingList = new List<MemberBinding>();

foreach (var sourceItem in sourceType.GetProperties())

{

var targetItem = targetType.GetProperty(sourceItem.Name);

if (targetItem == null || sourceItem.PropertyType != targetItem.PropertyType)

continue;

var property = Expression.Property(parameterExpression, sourceItem);

var memberBinding = Expression.Bind(targetItem, property);

memberBindingList.Add(memberBinding);

}

var memberInitExpression = Expression.MemberInit(Expression.New(targetType), memberBindingList);

var lambda = Expression.Lambda<Func<TSource, TTarget>>(memberInitExpression, parameterExpression );

Console.WriteLine(lambda);

return lambda.Compile();

}

调用如下

class Program

{

static void Main(string[] args)

{

var testA = new TestA { Id = 1, Name = "张三" };

var func = Map<TestA, TestB>();

TestB testB = func(testA);

Console.WriteLine($"testB.Id={testB.Id},testB.Name={testB.Name}");

Console.ReadLine();

}

}

输出结果

总结：此方法需要调用前需要手动编译下，然后再调用委托没有缓存委托，相对麻烦。

2、缓存实现

利用静态泛型类缓存泛型委托

public class DataMapper<TSource, TTarget>

{

private static Func<TSource, TTarget> MapFunc { get; set; }

public static TTarget Map(TSource source)

{

if (MapFunc == null)

MapFunc = GetMap();//方法在上边

return MapFunc(source);

}

}

调用方法

static void Main(string[] args)

{

var testA = new TestA { Id = 1, Name = "张三" };

TestB testB = DataMapper<TestA, TestB>.Map(testA);//委托不存在时自动生成，存在时调用静态缓存

Console.WriteLine($"testB.Id={testB.Id},testB.Name={testB.Name}");

Console.ReadLine();

}

输出结果

总结：引入静态泛型类能解决泛型委托缓存提高性能，但是有两个问题 1.当传入参数为null时则会抛出空引用异常 2.出现复杂类型上述方法便不能满足了

3、解决参数为空值和复杂类型的问题

首先先用常规代码实现下带有复杂类型赋值的情况

public TestB GetTestB(TestA testA)

{

TestB testB;

if (testA != null)

{

testB = new TestB();

testB.Id = testA.Id;

testB.Name = testA.Name;

if (testA.TestClass != null)

{

testB.TestClass = new TestD();

testB.TestClass.Id = testA.TestClass.Id;

testB.TestClass.Name = testA.TestClass.Name;

}

}

else

{

testB = null;

}

return testB;

}

将上面的代码翻译成表达式树

private static Func<TSource, TTarget> GetMap()

{

var sourceType = typeof(TSource);

var targetType = typeof(TTarget);

//Func委托传入变量

var parameter = Expression.Parameter(sourceType);

//声明一个返回值变量

var variable = Expression.Variable(targetType);

//创建一个if条件表达式

var test = Expression.NotEqual(parameter, Expression.Constant(null, sourceType));// p==null;

var ifTrue = Expression.Block(GetExpression(parameter, variable, sourceType, targetType));

var IfThen = Expression.IfThen(test, ifTrue);

//构造代码块

var block = Expression.Block(new[] { variable }, parameter, IfThen, variable);

var lambda = Expression.Lambda<Func<TSource, TTarget>>(block, parameter);

return lambda.Compile();

}

private static List<Expression> GetExpression(Expression parameter, Expression variable, Type sourceType, Type targetType)

{

//创建一个表达式集合

var expressions = new List<Expression>();

expressions.Add(Expression.Assign(variable, Expression.MemberInit(Expression.New(targetType))));

foreach (var targetItem in targetType.GetProperties().Where(x => x.PropertyType.IsPublic && x.CanWrite))

{

var sourceItem = sourceType.GetProperty(targetItem.Name);

//判断实体的读写权限

if (sourceItem == null || !sourceItem.CanRead || sourceItem.PropertyType.IsNotPublic)

continue;

var sourceProperty = Expression.Property(parameter, sourceItem);

var targetProperty = Expression.Property(variable, targetItem);

//判断都是class 且类型不相同时

if (targetItem.PropertyType.IsClass && sourceItem.PropertyType.IsClass && targetItem.PropertyType != sourceItem.PropertyType)

{

if (targetItem.PropertyType != targetType)//不处理嵌套循环的情况

{

//由于类型是class 所以默认值是null

var testItem = Expression.NotEqual(sourceProperty, Expression.Constant(null, sourceItem.PropertyType));

var itemExpressions = GetExpression(sourceProperty, targetProperty, sourceItem.PropertyType, targetItem.PropertyType);

var ifTrueItem = Expression.Block(itemExpressions);

var IfThenItem = Expression.IfThen(testItem, ifTrueItem);

expressions.Add(IfThenItem);

continue;

}

}

//目标值类型时且两者类型不一致时跳过

if (targetItem.PropertyType != sourceItem.PropertyType)

continue;

expressions.Add(Expression.Assign(targetProperty, sourceProperty));

}

return expressions;

}

总结：此方案，运用 Expression.IfThen(testItem, ifTrueItem) 判断空值问题，通过递归调用 GetExpression()方法，处理复杂类型。

但是。。。针对嵌套类仍然不能解决。因为表达式树是在实际调用方法之前就生成的，在没有实际的

参数值传入之前，生成的表达式是不知道有多少层级的。

有个比较low的方案是，预先设定嵌套层级为10层，然后生成一个有10层 if(P!=null) 的判断。如果传入的参数层级超过10层了呢，就得手动调整生成的树，此方案也否决。

最后得出的结论只能在表达式中动态调用方法。

4、最终版本

通过动态调用方法解决嵌套类，代码如下

using System.Collections;

using System;

using System.Collections.Generic;

using System.ComponentModel.DataAnnotations.Schema;

using System.Linq;

using System.Linq.Expressions;

using System.Reflection;

using static System.Linq.Expressions.Expression;

public static class Mapper<TSource, TTarget> where TSource : class where TTarget : class

{

private static Func<TSource, TTarget> MapFunc { get; set; }

public static TTarget Map(TSource source)

{

if (MapFunc == null)

MapFunc = GetMap();

return MapFunc(source);

}

public static List<TTarget> MapList(IEnumerable<TSource> sources)

{

if (MapFunc == null)

MapFunc = GetMap();

var result = new List<TTarget>();

foreach (var item in sources)

{

result.Add(MapFunc(item));

}

return result;

}

private static Func<TSource, TTarget> GetMap()

{

var sourceType = typeof(TSource);

var targetType = typeof(TTarget);

//Func委托传入变量

var parameter = Parameter(sourceType, "p");

var memberBindings = new List<MemberBinding>();

var targetTypes = targetType.GetProperties().Where(x => x.PropertyType.IsPublic && x.CanWrite);

foreach (var targetItem in targetTypes)

{

var sourceItem = sourceType.GetProperty(targetItem.Name);

//判断实体的读写权限

if (sourceItem == null || !sourceItem.CanRead || sourceItem.PropertyType.IsNotPublic)

continue;

//标注NotMapped特性的属性忽略转换

if (sourceItem.GetCustomAttribute<NotMappedAttribute>() != null)

continue;

var sourceProperty = Property(parameter, sourceItem);

//当非值类型且类型不相同时

if (!sourceItem.PropertyType.IsValueType && sourceItem.PropertyType != targetItem.PropertyType)

{

//判断都是(非泛型)class

if (sourceItem.PropertyType.IsClass && targetItem.PropertyType.IsClass &&

!sourceItem.PropertyType.IsGenericType && !targetItem.PropertyType.IsGenericType)

{

var expression = GetClassExpression(sourceProperty, sourceItem.PropertyType, targetItem.PropertyType);

memberBindings.Add(Expression.Bind(targetItem, expression));

}

//集合数组类型的转换

if (typeof(IEnumerable).IsAssignableFrom(sourceItem.PropertyType) && typeof(IEnumerable).IsAssignableFrom(targetItem.PropertyType))

{

var expression = GetListExpression(sourceProperty, sourceItem.PropertyType, targetItem.PropertyType);

memberBindings.Add(Expression.Bind(targetItem, expression));

}

continue;

}

if (targetItem.PropertyType != sourceItem.PropertyType)

continue;

memberBindings.Add(Bind(targetItem, sourceProperty));

}

//创建一个if条件表达式

var test = NotEqual(parameter, Constant(null, sourceType));// p==null;

var ifTrue = MemberInit(New(targetType), memberBindings);

var condition = Condition(test, ifTrue, Constant(null, targetType));

var lambda = Lambda<Func<TSource, TTarget>>(condition, parameter);

return lambda.Compile();

}

/// <summary>

/// 类型是clas时赋值

/// </summary>

/// <param name="sourceProperty"></param>

/// <param name="targetProperty"></param>

/// <param name="sourceType"></param>

/// <param name="targetType"></param>

/// <returns></returns>

private static Expression GetClassExpression(Expression sourceProperty, Type sourceType, Type targetType)

{

//条件p.Item!=null

var testItem = NotEqual(sourceProperty, Constant(null, sourceType));

//构造回调 Mapper<TSource, TTarget>.Map()

var mapperType = typeof(Mapper<,>).MakeGenericType(sourceType, targetType);

var iftrue = Call(mapperType.GetMethod(nameof(Map), new[] { sourceType }), sourceProperty);

var conditionItem = Condition(testItem, iftrue, Constant(null, targetType));

return conditionItem;

}

/// <summary>

/// 类型为集合时赋值

/// </summary>

/// <param name="sourceProperty"></param>

/// <param name="targetProperty"></param>

/// <param name="sourceType"></param>

/// <param name="targetType"></param>

/// <returns></returns>

private static Expression GetListExpression(Expression sourceProperty, Type sourceType, Type targetType)

{

//条件p.Item!=null

var testItem = NotEqual(sourceProperty, Constant(null, sourceType));

//构造回调 Mapper<TSource, TTarget>.MapList()

var sourceArg = sourceType.IsArray ? sourceType.GetElementType() : sourceType.GetGenericArguments()[0];

var targetArg = targetType.IsArray ? targetType.GetElementType() : targetType.GetGenericArguments()[0];

var mapperType = typeof(Mapper<,>).MakeGenericType(sourceArg, targetArg);

var mapperExecMap = Call(mapperType.GetMethod(nameof(MapList), new[] { sourceType }), sourceProperty);

Expression iftrue;

if (targetType == mapperExecMap.Type)

{

iftrue = mapperExecMap;

}

else if (targetType.IsArray)//数组类型调用ToArray()方法

{

iftrue = Call(mapperExecMap, mapperExecMap.Type.GetMethod("ToArray"));

}

else if (typeof(IDictionary).IsAssignableFrom(targetType))

{

iftrue = Constant(null, targetType);//字典类型不转换

}

else

{

iftrue = Convert(mapperExecMap, targetType);

}

var conditionItem = Condition(testItem, iftrue, Constant(null, targetType));

return conditionItem;

}

}

输出的表达式

格式化后

p => IIF((p != null),

new TestB()

{

Id = p.Id,

Name = p.Name,

TestClass = IIF(

(p.TestClass != null),

Map(p.TestClass),

null

),

TestLists = IIF(

(p.TestLists != null),

MapList(p.TestLists).ToArray(),

null

)

},

null)

说明 Map(p.TestClass) MapList(p.TestLists).ToArray(), 完整的信息为 Mapper<TestC,TestD>.Map() Mapper<TestC,TestD>.MapList()

总结：解决嵌套类的核心代码

//构造回调 Mapper<TSource, TTarget>.Map()

var mapperType = typeof(DataMapper<,>).MakeGenericType(sourceType, targetType);

var mapperExecMap = Expression.Call(mapperType.GetMethod(nameof(Map), new[] { sourceType }), sourceProperty);

利用Expression.Call 根据参数类型动态生成对象映射的表达式

性能测试

写了这么多最终目的还是为了解决性能问题，下面将对比下性能

1、测试类

public static class MapperTest

{

//执行次数

public static int Count = 100000;

//简单类型

public static void Nomal()

{

Console.WriteLine($"******************简单类型:{Count / 10000}万次执行时间*****************");

var model = new TestA

{

Id =1,

Name = "张三",

};

//计时

var sw = Stopwatch.StartNew();

for (int i = 0; i < Count; i++)

{

if (model != null)

{

var b = new TestB

{

Id = model.Id,

Name = model.Name,

};

}

}

sw.Stop();

Console.WriteLine($"原生的时间:{sw.ElapsedMilliseconds}ms");

Exec(model);

}

//复杂类型

public static void Complex()

{

Console.WriteLine($"********************复杂类型:{Count / 10000}万次执行时间*********************");

var model = new TestA

{

Id = 1,

Name = "张三",

TestClass = new TestC

{

Id = 2,

Name = "lisi",

},

};

//计时

var sw = Stopwatch.StartNew();

for (int i = 0; i < Count; i++)

{

if (model != null)

{

var b = new TestB

{

Id = model.Id,

Name = model.Name,

};

if (model.TestClass != null)

{

b.TestClass = new TestD

{

Id = i,

Name = "lisi",

};

}

}

}

sw.Stop();

Console.WriteLine($"原生的时间:{sw.ElapsedMilliseconds}ms");

Exec(model);

}

//嵌套类型

public static void Nest()

{

Console.WriteLine($"*****************嵌套类型:{Count / 10000}万次执行时间*************************");

var model = new TestA

{

Id = 1,

Name = "张三",

TestClass = new TestC

{

Id = 1,

Name = "lisi",

SelfClass = new TestC

{

Id = 2,

Name = "lisi",

SelfClass = new TestC

{

Id = 3,

Name = "lisi",

SelfClass = new TestC

{

Id = 4,

Name = "lisi",

},

},

},

},

};

//计时

var item = model;

var sw = Stopwatch.StartNew();

for (int i = 0; i < Count; i++)

{

//这里每一步需要做非空判断的，书写太麻烦省去了

if (model != null)

{

var b = new TestB

{

Id = model.Id,

Name = model.Name,

TestClass = new TestD

{

Id = model.TestClass.Id,

Name = model.TestClass.Name,

SelfClass = new TestD

{

Id = model.TestClass.SelfClass.Id,

Name = model.TestClass.SelfClass.Name,

SelfClass = new TestD

{

Id = model.TestClass.SelfClass.SelfClass.Id,

Name = model.TestClass.SelfClass.SelfClass.Name,

SelfClass = new TestD

{

Id = model.TestClass.SelfClass.SelfClass.SelfClass.Id,

Name = model.TestClass.SelfClass.SelfClass.SelfClass.Name,

},

},

},

},

};

}

}

sw.Stop();

Console.WriteLine($"原生的时间:{sw.ElapsedMilliseconds}ms");

Exec(model);

}

//集合

public static void List()

{

Console.WriteLine($"********************集合类型:{Count/10000}万次执行时间***************************");

var model = new TestA

{

Id = 1,

Name = "张三",

TestLists = new List<TestC> {

new TestC{

Id = 1,

Name = "张三",

},

new TestC{

Id = -1,

Name = "张三",

},

}

};

//计时

var sw = Stopwatch.StartNew();

for (int i = 0; i < Count; i++)

{

var item = model;

if (item != null)

{

var b = new TestB

{

Id = item.Id,

Name = item.Name,

TestLists = new List<TestD> {

new TestD{

Id = item.Id,

Name = item.Name,

},

new TestD{

Id = -item.Id,

Name = item.Name,

},

}.ToArray()

};

}

}

sw.Stop();

Console.WriteLine($"原生的时间:{sw.ElapsedMilliseconds}ms");

Exec(model);

}

public static void Exec(TestA model)

{

//表达式

Mapper<TestA, TestB>.Map(model);

var sw = Stopwatch.StartNew();

for (int i = 0; i < Count; i++)

{

var b = Mapper<TestA, TestB>.Map(model);

}

sw.Stop();

Console.WriteLine($"表达式的时间:{sw.ElapsedMilliseconds}ms");

//AutoMapper

sw.Restart();

for (int i = 0; i < Count; i++)

{

var b = AutoMapper.Mapper.Map<TestA, TestB>(model);

}

sw.Stop();

Console.WriteLine($"AutoMapper时间:{sw.ElapsedMilliseconds}ms");

//TinyMapper

sw.Restart();

for (int i = 0; i < Count; i++)

{

var b = TinyMapper.Map<TestA, TestB>(model);

}

sw.Stop();

Console.WriteLine($"TinyMapper时间:{sw.ElapsedMilliseconds}ms");

}

}

2、调用测试

static void Main(string[] args)

{

AutoMapper.Mapper.Initialize(cfg => cfg.CreateMap<TestA, TestB>());

TinyMapper.Bind<TestA, TestB>();

Mapper<TestA, TestB>.Map(new TestA());

MapperTest.Count = 10000;

MapperTest.Nomal();

MapperTest.Complex();

MapperTest.Nest();

MapperTest.List();

MapperTest.Count = 100000;

MapperTest.Nomal();

MapperTest.Complex();

MapperTest.Nest();

MapperTest.List();

MapperTest.Count = 1000000;

MapperTest.Nomal();

MapperTest.Complex();

MapperTest.Nest();

MapperTest.List();

MapperTest.Count = 10000000;

MapperTest.Nomal();

MapperTest.Complex();

MapperTest.Nest();

MapperTest.List();

Console.WriteLine($"------------结束--------------------");

Console.ReadLine();

}

3、结果

1万次

10万次

100万次

1000万次

上图结果AutoMapper 在非简单类型的转换上比其他方案有50倍以上的差距，几乎就跟反射的结果一样。

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