執行LINQ時獲取另一個對象

Question

我不知道如何解釋清楚。但是我試圖在LINQ語句執行時獲得另一個屬性。 例如：

這是一個工作LINQ聲明：

if (customerData.Demographics.Count > 0) 
{ 
    string[] communities = {"ONLINE_TECH_COMM", "ONLINE_PROF_NET", "ONLINE_TECH_SECTIONS"}; 
    var results = (from CustomerDemographic customerDemographic in customerData.Demographics where (customerDemographic.UserD2==DateTime.MinValue) 
      select new Models.MemberOnlineCommunityPreferences() 
      { 
       DemographicCode = customerDemographic.DemographicCodeString, 
       DemographicSubCode = customerDemographic.DemographicSubcodeString, 
    }).Where(x=>communities.Contains(x.DemographicCode)).OrderBy(x=>x.DemographicCode).ToList(); 

現在，我需要通過DemographicCodeString和DemographicSubcodeString值

oApplicationSubcode = TIMSS.API.CachedApplicationData.ApplicationDataCache.get_ApplicationSubCode("CUS", "DEMOGRAPHIC", DemographicCodeString, DemographicSubcodeString); 

而且，檢查性能WebEnabled =="Y"和Active=="Y"，然後只讀customerData並將其分配給結果。是否可以在單個語句中使用LINQ來完成此操作？

Answer 1

像這樣（完全未經測試）？

var results = (from CustomerDemographic customerDemographic in customerData.Demographics 
       where (customerDemographic.UserD2==DateTime.MinValue) 
        && communities.Contains(x.DemographicCodeString) 
       let applicationSubcode = TIMSS.API.CachedApplicationData.ApplicationDataCache.get_ApplicationSubCode("CUS", "DEMOGRAPHIC", customerDemographic.DemographicCodeString, customerDemographic.DemographicSubcodeString) 
       where applicationSubcode.WebEnabled == "Y" 
        && applicationSubcode.Active == "Y" 
       orderby customerDemographic.DemographicCodeString 
       select customerDemographic).ToList(); 

Answer 2

您需要使用「let」關鍵字。

https://msdn.microsoft.com/en-us/library/bb383976.aspx

var results = from CustomerDemographic customerDemographic in customerData.Demographics 

let code = customerDemographic.DemographicCodeString 

let subcode = customerDemographic.DemographicSubcodeString 

where communities.Contains(code) && customerDemographic.UserD2==DateTime.MinValue 

let appSubCode = TIMSS.API.CachedApplicationData.ApplicationDataCache.get_ApplicationSubCode("CUS", "DEMOGRAPHIC", code, subcode) 

where appSubCode.WebEnabled =="Y" && appSubCode.Active=="Y" 

select new Models.MemberOnlineCommunityPreferences() 
     { 
      DemographicCode = code, 
      DemographicSubCode = subcode 
     };