Mapper 实体转换Entiy to Dto

实际使用中发现很多问题 如果用EFcore 框架，这个表达式树生成一个新的实体
导致EFcore 跟踪失败！

/// <summary>
    /// 生成表达式目录树  泛型缓存
    /// </summary>
    /// <typeparam name="TIn"></typeparam>
    /// <typeparam name="TOut"></typeparam>
    public class ExpressionGenericMapper<TIn, TOut>//Mapper`2
    {
        private static Func<TIn, TOut> _FUNC = null;
        private static Func<TIn, TOut, TOut> _FUNC2 = null;
        public static TOut Trans(TIn t)
        {
            return _FUNC(t);
        }

        /// <summary>
        /// 批量实体转换
        /// </summary>
        /// <param name="list">被转换的实体List</param>
        /// <returns></returns>
        public static List<TOut> TransList(List<TIn> list)
        {
            List<TOut> outs = new List<TOut>();
            foreach (var item in list)
            {
                outs.Add(Trans(item));
            }
            return outs;
        }

        /// <summary>
        /// 把TOut 按照TIn来更新
        /// </summary>
        /// <param name="news"></param>
        /// <param name="old"></param>
        /// <returns></returns>
        public static TOut Modify(TIn news, TOut old)
        {
            return _FUNC2(news, old);
        }

        static ExpressionGenericMapper()
        {
            Type stringType = typeof(string);
            #region 创建构造对象的委托
            {
                ParameterExpression parameterExpression = Expression.Parameter(typeof(TIn), "m");
                List<MemberBinding> memberBindingList = new List<MemberBinding>();
                foreach (var item in typeof(TOut).GetProperties())
                {
                    var type = typeof(TIn);
                    if (item.PropertyType.IsClass && item.PropertyType != stringType)//排除String以外的引用类型，不进行赋值
                    {
                        continue;
                    }
                    var prop = type.GetProperty(item.GetMappingName());//从Out类找映射的字段名
                    if (prop != null)//如果TIn里能找到该属性
                    {

                        MemberExpression property = Expression.Property(parameterExpression, prop);
                        MemberBinding memberBinding = Expression.Bind(item, property);
                        memberBindingList.Add(memberBinding);
                    }
                }
                foreach (var item in typeof(TOut).GetFields())
                {
                    var type = typeof(TIn);
                    if (item.FieldType.IsClass && item.FieldType != stringType)//排除String以外的引用类型，不进行赋值
                    {
                        continue;
                    }
                    var prop = type.GetField(item.GetMappingName());//从Out类找映射的字段名
                    if (prop != null)
                    {
                        MemberExpression property = Expression.Field(parameterExpression, prop);
                        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();//拼装是一次性的
            }
            #endregion
            #region 修改对象的委托
            {

                ParameterExpression oExpression = Expression.Parameter(typeof(TOut), "o");
                ParameterExpression nExpression = Expression.Parameter(typeof(TIn), "n");
                List<MemberBinding> memberBindingList = new List<MemberBinding>();
                foreach (var item in typeof(TOut).GetProperties())
                {
                    var type = typeof(TIn);
                    if (item.PropertyType.IsClass && item.PropertyType != stringType)//排除String以外的引用类型，不进行赋值
                    {
                        continue;
                    }
                    var prop = type.GetProperty(item.GetMappingName());
                    if (prop != null)
                    {
                        MemberExpression property = Expression.Property(nExpression, prop);
                        MemberBinding memberBinding = Expression.Bind(item, property);
                        memberBindingList.Add(memberBinding);
                    }
                    else
                    {
                        var propOld = typeof(TOut).GetProperty(item.Name);
                        MemberExpression property = Expression.Property(oExpression, propOld);
                        MemberBinding memberBinding = Expression.Bind(item, property);
                        memberBindingList.Add(memberBinding);
                    }
                }
                foreach (var item in typeof(TOut).GetFields())
                {
                    var type = typeof(TIn);
                    if (item.FieldType.IsClass && item.FieldType != stringType)//排除String以外的引用类型，不进行赋值
                    {
                        continue;
                    }
                    var prop = type.GetField(item.GetMappingName());
                    if (prop != null)
                    {
                        MemberExpression property = Expression.Field(nExpression, prop);
                        MemberBinding memberBinding = Expression.Bind(item, property);
                        memberBindingList.Add(memberBinding);
                    }
                    else
                    {
                        var propOld = typeof(TOut).GetField(item.Name);
                        MemberExpression property = Expression.Field(oExpression, propOld);
                        MemberBinding memberBinding = Expression.Bind(item, property);
                        memberBindingList.Add(memberBinding);
                    }
                }
                MemberInitExpression memberInitExpression = Expression.MemberInit(Expression.New(typeof(TOut)), memberBindingList.ToArray());
                Expression<Func<TIn, TOut, TOut>> lambda = Expression.Lambda<Func<TIn, TOut, TOut>>(memberInitExpression, new ParameterExpression[]
                {
                   nExpression, oExpression
                });
                _FUNC2 = lambda.Compile();//拼装是一次性的
            }
            #endregion
        }

    }

    public static class ExpressionGenericMapperExtend
    {
        public static string GetMappingName(this PropertyInfo prop)
        {

            if (prop.IsDefined(typeof(MappingAttribute), true))
            {
                MappingAttribute display = prop.GetCustomAttribute(typeof(MappingAttribute)) as MappingAttribute;
                return display.MappingName;
            }
            return prop.Name;

        }

        public static string GetMappingName(this FieldInfo prop)
        {

            if (prop.IsDefined(typeof(MappingAttribute), true))
            {
                MappingAttribute display = prop.GetCustomAttribute(typeof(MappingAttribute)) as MappingAttribute;
                return display.MappingName;
            }
            return prop.Name;

        }
    }

    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
    public class MappingAttribute : Attribute
    {
        public string MappingName;
        public MappingAttribute(string _MappingName)
        {
            this.MappingName = _MappingName;
        }

    }