C＃使用linq枚举定义局部变量

Question

I need to define a local variable within a C# enumeration as I have an additional enumeration with that which is called several times creating inefficiencies. The code currently looks like this:

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}
);

I actually have numerous enumerations of the workDataList list, but I'm selecting on the same item each time (EmployeeID). Is there some way I can just select my individual workDataList object once, then use it for all assignments within each individual from select loop.

The code above is a simplified version so names, data structures are just created for descriptive clarity.

Let me know if I can provide any additional information.

Thanks!

Answer 1

I think you're looking for 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 
                                 }
);

You should use the let keyword. Here is a thoroughly explanation of the usage.