C#List.Clear()方法沒有得到正確的回應

我正在嘗試使用以下代碼將以下類映射到目標類。這里試圖將 Employee 類映射到

        static void Main(string[] args)
        {
            var emp = new List<Employee>()
            {
                new Employee()
                {
                    FirstName = "Test",
                    LastName = "Performance",
                    ID="1",
                    Availabities = new List<Availability>()
                    {
                        new Availability()
                        {
                            BeginDate = DateTime.Now,
                            EndDate = DateTime.Now.AddDays(1)
                        }
                    }
                 },
                 new Employee()
                 {
                     FirstName = "Test1",
                     LastName = "Performance1",
                     ID="2",
                     Availabities = new List<Availability>()
                    {
                        new Availability()
                        {
                            BeginDate = DateTime.Now,
                            EndDate = DateTime.Now.AddDays(10)
                        }
                     }
                 },
                  new Employee()
                 {
                     FirstName = "Test123",
                     LastName = "Performance1",
                     ID="3",
                     Availabities = new List<Availability>()
                    {
                        new Availability()
                        {
                            BeginDate = DateTime.Now,
                            EndDate = DateTime.Now.AddDays(5)
                        },
                        new Availability()
                        {
                            BeginDate = DateTime.Now,
                            EndDate = DateTime.Now.AddDays(3)
                        }
                     }
                 }
            };

這是目標物件映射，這里是要與 EmployeeDest 映射的 Employee。

            List<AvailabilityDest> empAvailabilitiesDest = new List<AvailabilityDest>();

            var results = new List<EmployeeDest>();

            foreach (var token in emp)
            {
                empAvailabilitiesDest.Clear();

                foreach (var item in token.Availabities)
                {
                    
                    var empAvailability = new AvailabilityDest
                    {
                        BeginDateDest = item.BeginDate,
                        EndDateDest = item.EndDate,
                    };
                        empAvailabilitiesDest.Add(empAvailability);
                }
                var employee = new EmployeeDest
                {
                    FirstNameDest = token.FirstName,
                    LastNameDest = token.LastName,
                   IDDest =token.ID,
                    AvailabitiesDest = empAvailabilitiesDest
                };
                results.Add(employee);
               
            }
            Console.WriteLine(results);
        }

這里empAvailabilitiesDest.Clear()沒有清除串列，并且availabilityDest每次迭代都會增加。

我在這里遺漏了一些東西。

2. 如何優化此處的代碼以獲得更好的性能？

uj5u.com熱心網友回復：

大概這里真正的問題是您的所有員工物件都共享同一個串列；無論您是否清除它，添加東西等都沒有關系：如果有一個串列并且它在所有員工之間共享，那么對該串列的更改將針對每個員工顯示，并且它看起來不正確。

大概，您真的只想將串列創建移動到每個員工內部：foreach

var results = new List<EmployeeDest>();
foreach (var token in emp)
{
    List<AvailabilityDest> empAvailabilitiesDest = new List<AvailabilityDest>
();
    // your previous code unchanged
}

uj5u.com熱心網友回復：

1.代碼中的問題

        var employee = new EmployeeDest
        {
            FirstNameDest = token.FirstName,
            LastNameDest = token.LastName,
            IDDest = token.ID,
            AvailabitiesDest = empAvailabilitiesDest // This is problematic code
        };

由于上面的代碼，每個 empolyee.AvailabitiesDest 都將參考同一個物件，因為它不是原始型別變數。您必須將物件的副本分配給employee.AvailabitiesDest，

        var employee = new EmployeeDest
        {
            FirstNameDest = token.FirstName,
            LastNameDest = token.LastName,
            IDDest = token.ID,
            AvailabitiesDest = new List<AvailabilityDest>(empAvailabilitiesDest)
        };

2.簡化代碼

使用 Linq。

        results = emp.Select(token => new EmployeeDest
        {
            FirstNameDest = token.FirstName,
            LastNameDest = token.LastName,
            IDDest = token.ID,
            AvailabitiesDest = token.Availabities.Select(item => new AvailabilityDest
            {
                BeginDateDest = item.BeginDate,
                EndDateDest = item.EndDate,
            }).ToList()
        }).ToList();

或者使用 AutoMapper

    var mapper = new Mapper(new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<Employee, EmployeeDest>()
            .ForMember(x => x.FirstNameDest, opt => opt.MapFrom(src => src.FirstName))
            .ForMember(x => x.LastNameDest, opt => opt.MapFrom(src => src.LastName))
            .ForMember(x => x.IDDest, opt => opt.MapFrom(src => src.ID))
            .ForMember(x=> x.AvailabitiesDest, opt => opt.MapFrom(src => src.Availabities));
        cfg.CreateMap<Availability, AvailabilityDest>()
            .ForMember(x => x.BeginDateDest, opt => opt.MapFrom(src => src.BeginDate))
            .ForMember(x => x.EndDateDest, opt => opt.MapFrom(src => src.EndDate));
    }));

    var results = mapper.Map<List<EmployeeDest>>(emp);

標籤：C＃ asp.net-mvc asp.net 核心 映射 自动映射器

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