Expression动态生成方法例子

实现和上个用DynamicMethod的方式生成的复制实体类对应一样功能

public  static class  ExpMapper<TTarget,TSource>
    {
        private static MapMethod<TTarget, TSource> mapMethod;
          public static MapMethod<TTarget, TSource> GetMapMethod()
        {
            if (mapMethod == null)
            {
                mapMethod = CreateMapMethod(typeof(TTarget), typeof(TSource));
            }
            return mapMethod;
        }

        public static TTarget Map(TSource source)
        {
            if (mapMethod == null)
            {
                mapMethod = CreateMapMethod(typeof(TTarget), typeof(TSource));
            }
            return mapMethod(source);     
        }

        private static MapMethod<TTarget, TSource> CreateMapMethod(Type targetType, Type sourceType)
        {
            var source = Expression.Parameter(sourceType, "source");
   
            var binds = (from sp in sourceType.GetProperties()
                              from tp in targetType.GetProperties()
                              where sp.Name == tp.Name
                              select Expression.Bind(tp, Expression.Property(source, sp))).ToArray();

            Expression body = Expression.MemberInit(Expression.New(typeof(TTarget)), binds);

            return Expression.Lambda<MapMethod<TTarget, TSource>>(body,source).Compile();
                             
        }

    }