LINQ到Entites和ObjectQuery

Question

我有與Person_Addresses（字段：PersonID,AddressID,ValidFrom）有1：N關係的Person實體。我想獲得所有Person記錄和關聯Person_Addresses只有最新的ValidFrom。我應該如何使用ObjectQuery或IQueryable來做到這一點？

編輯： 我提到ObjectQuery和IQueryable，因爲我想有使用擴展方法（我想，那它是如何稱呼）的解決方案。另外我忘了提及我在使用Entity Framework的地方生成實體。我想獲得一個person_adress成員熱切加載的person對象。

這裏是實體結構： 人成員：INT ID，串名字，姓氏字符串，Partner_Address partneradress

Person_Address成員：int personid，int adressid，date validfrom

Answer 1

嘗試以下。

我有以下實體。

//Person Entity 
    public class Person 
    { 
     public int PersonID { get; set; } 
     public string PersonName { get; set; } 
    } 

    //PersonAddress Entity 
    public class PersonAddress 
    { 
     public int PersonID { get; set; } 
     public int AddressID { get; set; } 
     public DateTime ValidFrom { get; set; } 
    } 

然後激發以下查詢。

//Get the latest ValidFrom for each person from PersonAddress. 
    var getLatestDateRecords = 
    from p in lstPersonAddress 
    group p by p.PersonID into g 
    select new 
    { 
     Infos = 
      (from PA in g 
      select new 
      { 
       PersonId = PA.PersonID 
       Date = g.Max(t=>t.ValidFrom) 
      }).Distinct() 
    }; 

    //Segregate the ValidFroms and PersonId from the 
    //previous record set(getLatestDateRecords). 
    var segRecords = 
     from x in getLatestDateRecords 
     from y in x.Infos 
     select new { Date = y.Date, PersonId = y.PersonId }; 

    //Obtain all the relevant information from the PersonAddress 
    // for the latest ValidFrom dates. 
    var allValidRecords = 
     from PA in lstPersonAddress 
     join x in segRecords 
     on PA.ValidFrom equals x.Date 
     where PA.PersonID == x.PersonId 
     select new { 
       PersonId = PA.PersonID 
       , AddressId = PA.AddressID 
       , Date = PA.ValidFrom 
      }; 

    //Get the final result 
    var resultSet = 
     from p in lstPerson 
     join x in allValidRecords 
     on p.PersonID equals x.PersonId 
     select new 
     { 
      PersonId = p.PersonID 
      ,PersonName = p.PersonName 
      ,AddressId = x.AddressId, 
      Date = x.Date 
     }; 

我發現它與一些測試數據工作正常。

如有任何問題，請告知我。