返回linq查詢的結果時方法的輸出類型是什么？

Question

我使用Linq查詢而不是使用Sqlserver的視圖。 我想將其放在方法中。我的輸出類型是什么？ 謝謝你的幫助

public ???? InsuranceWorkerView()
{
    var InsuranceWorkers =(from ins_insuranceworkers in db.INS_InsuranceWorkers
         join dv in db.DivisionCountry on new { InsWorkerCityID = ins_insuranceworkers.InsWorkerCityID } equals new { InsWorkerCityID = dv.DivisionID } into divisioncountry_1_join
         from dv in divisioncountry_1_join.DefaultIfEmpty()
         join divisioncountry in db.DivisionCountry on new { InsWorkerStateID = ins_insuranceworkers.InsWorkerStateID } equals new { InsWorkerStateID = divisioncountry.DivisionID } into divisioncountry_join
         from divisioncountry in divisioncountry_join.DefaultIfEmpty()
         select new 
         {
            ins_insuranceworkers.InsWorkerID,
            ins_insuranceworkers.InsWorkerCreateUserID,
             ins_insuranceworkers.InsWorkerTypeID,
             ins_insuranceworkers.InsWorkerFirstName,
             ins_insuranceworkers.InsWorkerLastName,  
            ins_insuranceworkers.InsWorkerNationalCode,
             ins_insuranceworkers.InsWorkerMobileNum,
             ins_insuranceworkers.InsWorkerAddress,
             ins_insuranceworkers.InsWorkerEmail,
              City = dv.DivisionName,
              State = divisioncountry.DivisionName,
             InsWorkerStateID =(Int32?)ins_insuranceworkers.InsWorkerStateID,
             InsWorkerCityID = (Int32?)ins_insuranceworkers.InsWorkerCityID
         }).ToList();

    return InsuranceWorkers;
}

Answer 1

不幸的是，您不能從方法中返回匿名類型 ：

您不能將字段，屬性，事件或方法的返回類型聲明為具有匿名類型。 同樣，您不能將方法，屬性，構造函數或索引器的形式參數聲明為具有匿名類型。 要將匿名類型或包含匿名類型的集合作為方法的參數傳遞，可以將參數聲明為類型對象。

因此，要么為此數據創建一些特定類型並返回它：

public List<Foo> InsuranceWorkerView()
{
    return (from i in db.INS_InsuranceWorkers
            select new Foo {
                InsWorkerID = i.InsWorkerID,
                InsWorkerCreateUserID = i.InsWorkerCreateUserID
                // etc
            }).ToList();
}

或返回object （我發現它沒什么用）：

public object InsuranceWorkerView()
{
    return (from i in db.INS_InsuranceWorkers
            select new {
                i.InsWorkerID,
                i.InsWorkerCreateUserID
                // etc
            }).ToList();
}

Answer 2

當動態可能派上用場時就是這種情況。

public IEnumerable<dynamic> InsuranceWorkerView()
{
    var InsuranceWorkers =(from ins_insuranceworkers in db.INS_InsuranceWorkers
         join dv in db.DivisionCountry on new { InsWorkerCityID = ins_insuranceworkers.InsWorkerCityID } equals new { InsWorkerCityID = dv.DivisionID } into divisioncountry_1_join
         from dv in divisioncountry_1_join.DefaultIfEmpty()
         join divisioncountry in db.DivisionCountry on new { InsWorkerStateID = ins_insuranceworkers.InsWorkerStateID } equals new { InsWorkerStateID = divisioncountry.DivisionID } into divisioncountry_join
         from divisioncountry in divisioncountry_join.DefaultIfEmpty()
         select new 
         {
            ins_insuranceworkers.InsWorkerID,
            ins_insuranceworkers.InsWorkerCreateUserID,
             ins_insuranceworkers.InsWorkerTypeID,
             ins_insuranceworkers.InsWorkerFirstName,
             ins_insuranceworkers.InsWorkerLastName,  
            ins_insuranceworkers.InsWorkerNationalCode,
             ins_insuranceworkers.InsWorkerMobileNum,
             ins_insuranceworkers.InsWorkerAddress,
             ins_insuranceworkers.InsWorkerEmail,
              City = dv.DivisionName,
              State = divisioncountry.DivisionName,
             InsWorkerStateID =(Int32?)ins_insuranceworkers.InsWorkerStateID,
             InsWorkerCityID = (Int32?)ins_insuranceworkers.InsWorkerCityID
         }).ToList();

    return InsuranceWorkers;
}

然后，您可以使用類似：

foreach (var worker in InsuranceWorkerView()) {
   var id = (int)worker.InsWorkerID;
}

Answer 3

您可以將新列表作為IList返回。

public IList InsuranceWorkerView()
{
    var InsuranceWorkers =(from ins_insuranceworkers in db.INS_InsuranceWorkers
         join dv in db.DivisionCountry on new { InsWorkerCityID = ins_insuranceworkers.InsWorkerCityID } equals new { InsWorkerCityID = dv.DivisionID } into divisioncountry_1_join
         from dv in divisioncountry_1_join.DefaultIfEmpty()
         join divisioncountry in db.DivisionCountry on new { InsWorkerStateID = ins_insuranceworkers.InsWorkerStateID } equals new { InsWorkerStateID = divisioncountry.DivisionID } into divisioncountry_join
         from divisioncountry in divisioncountry_join.DefaultIfEmpty()
         select new 
         {
            ins_insuranceworkers.InsWorkerID,
            ins_insuranceworkers.InsWorkerCreateUserID,
             ins_insuranceworkers.InsWorkerTypeID,
             ins_insuranceworkers.InsWorkerFirstName,
             ins_insuranceworkers.InsWorkerLastName,  
            ins_insuranceworkers.InsWorkerNationalCode,
             ins_insuranceworkers.InsWorkerMobileNum,
             ins_insuranceworkers.InsWorkerAddress,
             ins_insuranceworkers.InsWorkerEmail,
              City = dv.DivisionName,
              State = divisioncountry.DivisionName,
             InsWorkerStateID =(Int32?)ins_insuranceworkers.InsWorkerStateID,
             InsWorkerCityID = (Int32?)ins_insuranceworkers.InsWorkerCityID
         }).ToList();

並訪問該項目

   foreach(var item in InsuranceWorkers)
   {
      var a=   item.InsWorkerID; // to access the anonymous items
   }
}

Answer 4

為簡化起見，我建議您創建一種具有所需屬性的POCO類，以便正確表示所需的投影，而不是將其選擇為匿名類型並參與到惱人的危險鑄件中。

創建您的POCO類為：

public class InsuranceWorker
{
  public int InsWorkerId {get;set;}
  public int InsWorkerCreateUserId {get;set;}

  //Keep add the necessary properties here...
}

用法：

將您的匿名選擇（ select new ）語句替換為我們上面剛剛創建的已知類型：

 select new InsuranceWorker
 {
    InsWorkerId = ins_insuranceworkers.InsWorkerID,
    InsWorkerCreateUserId = ins_insuranceworkers.InsWorkerCreateUserID,
    //....
 }).ToList();

並返回IList<InsuranceWorker> ：

public IList<InsuranceWorker> InsuranceWorkerView()
{
  ....
}