C# 類對映的四種方法【解決硬編碼的問題】（工具三）

方法一：泛型快取+表示式目錄樹實現Mapper

public class ExpressionGenericMapper<TIn, TOut>//Mapper`2 //正對於每兩個不同型別的組合都會生成副本
    {
        private static Func<TIn, TOut> _FUNC = null;// 在每個副本中都有一個委託
        static ExpressionGenericMapper() //靜態建構函式 生成表示式目錄樹 
        {
            ParameterExpression parameterExpression = Expression.Parameter(typeof(TIn), "p");
            List<MemberBinding> memberBindingList = new List<MemberBinding>();
            foreach (var item in typeof(TOut).GetProperties())
            {
                MemberExpression property = Expression.Property(parameterExpression, typeof(TIn).GetProperty(item.Name));
                MemberBinding memberBinding = Expression.Bind(item, property);
                memberBindingList.Add(memberBinding);
            }
            foreach (var item in typeof(TOut).GetFields())
            {
                MemberExpression property = Expression.Field(parameterExpression, typeof(TIn).GetField(item.Name));
                MemberBinding memberBinding = Expression.Bind(item, property);
                memberBindingList.Add(memberBinding);
            }
            MemberInitExpression memberInitExpression = Expression.MemberInit(Expression.New(typeof(TOut)), memberBindingList.ToArray());
            Expression<Func<TIn, TOut>> lambda = Expression.Lambda<Func<TIn, TOut>>(memberInitExpression, new ParameterExpression[]
            {
                    parameterExpression
            });
            _FUNC = lambda.Compile();//拼裝是一次性的   轉換成委託以後放入副本的靜態變數中去
        }
        public static TOut Trans(TIn t) // 直接獲取副本的靜態變數（委託）
        {
            return _FUNC(t);
        }
    }

方法二：序列化和反序列化實現Mapper

    public class SerializeMapper
    {
        /// <summary>
        /// 序列化反序列化方式
        /// </summary>
        /// <typeparam name="TIn"></typeparam>
        /// <typeparam name="TOut"></typeparam>
        public static TOut Trans<TIn, TOut>(TIn tIn)
        {
            return JsonConvert.DeserializeObject<TOut>(JsonConvert.SerializeObject(tIn));
        }
    }

方法三：表示式目錄樹實現Mapper

    public class ExpressionMapper
    {
        /// <summary>
        /// 字典快取--hash分佈  
        /// </summary>
        private static Dictionary<string, object> _Dic = new Dictionary<string, object>();  //超過一定的數量之後  在字典中獲取值就會有效能損耗

        /// <summary>
        /// 字典快取表示式樹
        /// </summary>
        /// <typeparam name="TIn"></typeparam>
        /// <typeparam name="TOut"></typeparam>
        /// <param name="tIn"></param>
        /// <returns></returns>
        public static TOut Trans<TIn, TOut>(TIn tIn)
        {
            string key = string.Format("funckey_{0}_{1}", typeof(TIn).FullName, typeof(TOut).FullName);
            if (!_Dic.ContainsKey(key))
            {
                //動態的生成表示式
                ParameterExpression parameterExpression = Expression.Parameter(typeof(TIn), "p");
                List<MemberBinding> memberBindingList = new List<MemberBinding>();
                foreach (var item in typeof(TOut).GetProperties())
                {
                    MemberExpression property = Expression.Property(parameterExpression, typeof(TIn).GetProperty(item.Name));
                    MemberBinding memberBinding = Expression.Bind(item, property);
                    memberBindingList.Add(memberBinding);
                }
                foreach (var item in typeof(TOut).GetFields())
                {
                    MemberExpression property = Expression.Field(parameterExpression, typeof(TIn).GetField(item.Name));
                    MemberBinding memberBinding = Expression.Bind(item, property);
                    memberBindingList.Add(memberBinding);
                }
                MemberInitExpression memberInitExpression = Expression.MemberInit(Expression.New(typeof(TOut)), memberBindingList.ToArray());
                Expression<Func<TIn, TOut>> lambda = Expression.Lambda<Func<TIn, TOut>>(memberInitExpression, new ParameterExpression[]
                {
                    parameterExpression
                });
                Func<TIn, TOut> func = lambda.Compile();//拼裝是一次性的
                _Dic[key] = func;
            }
            return ((Func<TIn, TOut>)_Dic[key]).Invoke(tIn);
        }
    }

方法四：反射實現Mapper

public static TOut Trans<TIn, TOut>(TIn tIn)
        {
            TOut tOut = Activator.CreateInstance<TOut>();
            foreach (var itemOut in tOut.GetType().GetProperties())
            {
                var propIn = tIn.GetType().GetProperty(itemOut.Name);
                itemOut.SetValue(tOut, propIn.GetValue(tIn)); 
            }
            foreach (var itemOut in tOut.GetType().GetFields())
            {
                var fieldIn = tIn.GetType().GetField(itemOut.Name);
                itemOut.SetValue(tOut, fieldIn.GetValue(tIn)); 
            }
            return tOut;
        }

四種方式的比較第一種方法效能最好通用性最強