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
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