C＃使用linq枚舉定義局部變量

Question

我需要在C＃枚舉中定義一個局部變量，因為我有一個額外的枚舉，該枚舉多次被稱為創建效率低下。 當前代碼如下：

List<object> listData = new List<object>();
List<EmployeeAdvanced> workDataList = GetEmployeeWorkAdvancedData();
List<EmployeeBasic> employeeList = GetEmployeeBasicData();

listData .AddRange(
          from employee in employeeList
          where employee.SomeNumber  > 0
             select new{
             ID = employee.ID,
             SSN = employee.SSN
             StreetAddress = workDataList.FirstOrDefault(x=> x.ID==employee.EmployeeID).Address,
             Zipcode = workDataList.FirstOrDefault(x=> x.ID==employee.EmployeeID).Zipcode}
);

實際上，我有許多workDataList列表的枚舉，但是每次都在同一項上選擇（EmployeeID）。 有什么方法可以只選擇我的單個workDataList對象一次，然后將其用於select循環中每個個體內的所有分配。

上面的代碼是簡化的版本，因此僅為了描述清楚而創建了名稱和數據結構。

讓我知道是否可以提供其他信息。

謝謝！

Answer 1

我認為您正在尋找let 。

List<object> listData = new List<object>();
List<EmployeeAdvanced> workDataList = GetEmployeeWorkAdvancedData();
List<EmployeeBasic> employeeList = GetEmployeeBasicData();

listData .AddRange(
          from employee in employeeList
          where employee.SomeNumber  > 0
          let workData = workDataList.FirstOrDefault(x=> x.ID==employee.EmployeeID)
             select new{
             ID = employee.ID,
             SSN = employee.SSN
             StreetAddress = workData.Address,
             Zipcode = workData.Zipcode}
);

Answer 2

listData.AddRange(from employee in employeeList
                  where employee.SomeNumber  > 0
                      let employeeTmp = workDataList.FirstOrDefault(x => x.ID == employee.EmployeeID)
                      select new {
                                    ID = employee.ID,
                                    SSN = employee.SSN
                                    StreetAddress = employeeTmp.Address,
                                    Zipcode = employeeTmp.Zipcode 
                                 }
);

您應該使用let關鍵字。 這是用法的完整說明。