前言

NET Core(开放源代码,跨平台,x-copy可部署等)有许多令人兴奋的方面,其中最值得称赞的就是其性能了。关于对象转换已经有不少轮子(AutoMapper,TinyMapper) .出于项目需要，手动造一个简单轮子。下面话不多说了，来一起看看详细的介绍吧。

示例代码

g>1.采用静态泛型类缓存，避免了拆箱装箱操作。

2.对于转换对象中有，字段名一样但是类型不一样的类时仍可以用

public static class Mapper<TSource, TTarget> where TSource : class where TTarget : class
 {
 public readonly static Func<TSource, TTarget> Map;

 static Mapper()
 {
 if (Map == null)
 Map = GetMap();
 }

 private static Func<TSource, TTarget> GetMap()
 {
 var sourceType = typeof(TSource);
 var targetType = typeof(TTarget);

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

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

 /// <summary>
 /// 根据转换源和目标获取表达式树
 /// </summary>
 /// <param name="parameterExpression">表达式参数p</param>
 /// <param name="sourceType">转换源类型</param>
 /// <param name="targetType">转换目标类型</param>
 /// <returns></returns>
 private static MemberInitExpression GetExpression(Expression parameterExpression, Type sourceType, Type targetType)
 {
 var memberBindings = new List<MemberBinding>();
 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;

 //标注NotMapped特性的属性忽略转换
 if (sourceItem.GetCustomAttribute<NotMappedAttribute>() != null)
 continue;

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

 //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)//防止出现自己引用自己无限递归
 {
 var memberInit = GetExpression(propertyExpression, sourceItem.PropertyType, targetItem.PropertyType);
 memberBindings.Add(Expression.Bind(targetItem, memberInit));
 continue;
 }
 }

 if (targetItem.PropertyType != sourceItem.PropertyType)
 continue;

 memberBindings.Add(Expression.Bind(targetItem, propertyExpression));
 }
 return Expression.MemberInit(Expression.New(targetType), memberBindings);
 }
 }

3.调用方法如下

 （1）构造样例类

public class A
{
 public int Id { get; set; }
 public string Name { get; set; }
 public C User { get; set; }
 
 /// <summary>
 /// 标注为notmapped特性时，不转换赋值
 /// </summary>
 [System.ComponentModel.DataAnnotations.Schema.NotMapped]
 public D UserA { get; set; }
 
}
 
public class B
{
 public int Id { get; set; }
 public string Name { get; set; }
 public D User { get; set; }<br data-filtered="filtered">
 public D UserA { get; set; }
}
 
public class C
{
 public int Id { get; set; }
 public string Name { get; set; }
}
 
public class D
{
 public int Id { get; set; }
 public string Name { get; set; }
}

  (2) 调用

var a = new A
{
 Id = 1,
 Name = "张三",
 User = new C
 {
 Id = 1,
 Name = "李四"
 }
};<br>
B b = Mapper<A, B>.Map(a);//得到转换结果

4.性能测试

var length = 10000000;
 var listA = new List<A>();
 for (int i = 0; i < length; i++)
 {
 listA.Add(new A
 {
 Id = i,
 Name = "张三",
 User = new C
 {
 Id = i,
 Name = "李四"
 }
 });
 }

 var sw = Stopwatch.StartNew();
 for (int i = 0; i < length; i++)
 {
 var item = listA[i];
 var b = new B
 {
 Id = item.Id,
 Name = item.Name,
 User = new D
 {
 Id = i,
 Name = "李四",
 }
 };
 }
 sw.Stop();
 Console.WriteLine($"原生的时间:{sw.ElapsedMilliseconds}ms");

 //表达式
 Mapper<A, B>.Map(listA[0]);//预先编译缓存
 sw.Restart();
 for (int i = 0; i < length; i++)
 {
 Mapper<A, B>.Map(listA[i]);
 }
 sw.Stop();
 Console.WriteLine($"表达式的时间:{sw.ElapsedMilliseconds}ms");

 //AutoMapper
 AutoMapper.Mapper.Initialize(cfg => cfg.CreateMap<A, B>());
 sw.Restart();
 for (int i = 0; i < length; i++)
 {
 var b = AutoMapper.Mapper.Map<B>(listA[i]);
 }
 sw.Stop();
 Console.WriteLine($"AutoMapper时间:{sw.ElapsedMilliseconds}ms");

 //TinyMapper
 TinyMapper.Bind<A, B>();
 sw.Restart();
 for (int i = 0; i < length; i++)
 {
 var b = TinyMapper.Map<B>(listA[i]);
 }
 sw.Stop();
 Console.WriteLine($"TinyMapper时间:{sw.ElapsedMilliseconds}ms");

 Console.ReadLine();

5. 1000万数据不带子类集结果

6. 1000万数据带子类集结果　

总结