如何跳過空值并解決錯誤：值不能為空-有解無憂

我如何解決這個錯誤：

 Value cannot be null

這是模型：

public class Orders_Tables
{
   // internal IQueryable<object> result { get; set; }
    public Lab_Orders  LabOrders { get; set; }
    public Lab_orders_Cash LabOrdersCash { get; set; }
    public Lab_Sample_status LabOrderStatus { get; set; }

    public IEnumerable<LAB_RESULTS> LabResults { get; set; }

    public IEnumerable<TestsRanges> testsRanges { get; set; }

    public IEnumerable<TestsUnits>  testUnits { get; set; }

    public IEnumerable<LAB_CULTURE_RESULT> LabCultureResults { get; set; }

    public IEnumerable<LAB_MICRO_NEGATIVE_RESULT> LabMicroResults { get; set; }
    public IEnumerable<LabTests> labtests { get; set; }
    public IEnumerable<LAB_RESULTS_CLINIC_VIEW> labClinicsViewResult { get; set; }
    public IEnumerable<LAB_RESULT_CASH_VIEW> labCashView { get; set; }

    public IEnumerable<LAB_PARASITOLOGY_VIEW> LabParasitologyView { get; set; }

    public IEnumerable<LAB_CULTURES_VIEW> LabCulturesView { get; set; }

    public IEnumerable<LAB_MICRO_VIEW> LabMicroView { get; set; }

    public IEnumerable<LAB_HISTOPATHOLOGY_VIEW> LabHistopathologyView { get; set; }

    public IEnumerable<LAB_HISTO_RESULT> LabHistoResult { get; set; }

    public IEnumerable<LAB_PARA_RESULTS> LabParaResult { get; set; }

    public Lab_Hematology_Samples LabSamples { get; set; }

    public IEnumerable<LAB_URINE_ANALYSIS_RESULT> LabUrineResult { get; set; }
    public IEnumerable<LAB_URINE_RESULT_VIEW> LaburineView { get; set; }

  public Patients patients { get; set; }

    public IEnumerable<Customers> customers { get; set; }

}

這是我使用 Model.order_table 的視圖：

  @model IEnumerable<AljawdahNewSite.Models.Orders_Tables>
@{
    ViewBag.Title = "Clinics Orders";
    //Layout = "~/Views/Shared/_LayoutPatients.cshtml";
}
<link rel="stylesheet" [email protected]("/Content/bootstrap.min.css")>
<link rel="stylesheet" [email protected]("/Content/style.css")>
     <li><img width="500" height="100" style="margin-left:300px" src="~/Contents/images/mamlakaheader.png" />  <a href="~/Views/Orders/Clinicsorders.cshtml"></a></li>
    <li style="margin-left:1200px"><a [email protected]("Logout", "Login")><span class="d-inline-block bg-primary text-white btn btn-primary">Logout - ????? ?????? </span></a></li>
    <li style="margin-left:500px"> @Html.ActionLink("Welcome "   Session["UserFullname"], "Clinicsorders", "Orders") </li>
    <h3 style="text-align:center;color:coral;padding:10px;margin-left:500px">Orders List</h3>
    


<style> a {color: brown;text-decoration: wavy;text-shadow: 20px;font-size:medium;} a:hover {color: blue;}</style>

@using (Html.BeginForm("Clinicsorders", "Orders", FormMethod.Get))
{ 
    <div class="vertical-top">
        <span id="FromDate" style="margin-left:60px;color:red;font-size:large"><b>From Date</b></span><input id="FromDatetext" style="margin-left:10px" type="text" name="startdate" />
        <span id="ToDate" style="margin-left:95px;color:red;font-size:large"><b>To Date</b></span><input id="ToFatetext" type="text" style="margin:10px" name="enddate" /><br /><br />
      <span id="PCfileno" style="color:red;font-size:large"><b>Polyclinic File No</b></span><input id="PCFILENOTEXT" style="margin-left:10px" type="text" name="pcfileno" />
      <span id="IDNO" style="color:red;font-size:large;margin-left:30px"><b>ID or Iqama No</b></span><input id="idnotext" type="text" style="margin:10px" name="idno" />
      <span id="passport" style="color:red;font-size:large"><b>Passport No</b></span><input id="passporttext" style="margin-left:10px" type="text" name="Passport" />
      <span id="mobile" style="color:red;font-size:large;margin-left:30px"><b>Mobile No</b></span><input id="mobiletext" type="text" style="margin:10px" name="Mobile" />
        <input id="Submit1" type="submit" value="Search" class="btn btn-dark" />
    </div>
}
<table class="table">
    <tr>
        <td> Patient Name </td>
        <td> Order No. </td>
        <td> Test Id</td>
        <td> order date    </td>
        <td> Polyclinic File </td>
        <td> Order Status   </td>


    </tr>
    @foreach (var item in Model)
    {
        <tr>
            <td>@item.patients.Patient_Name</td>
            <td>@item.LabOrders.ORDER_ID</td>
            <!--Here is one-->
            <td>@(item.LabCultureResults?.FirstOrDefault()?.TESTID.HasValue ? item.LabCultureResults?.FirstOrDefault()?.TESTID : "No Test ID" )</td>
            <td>@item.LabOrders.ORDER_DATE</td>
            <td>@item.patients.PCfileNO</td>
            <td>@item.LabOrderStatus.status_name</td>
            <td>@Html.ActionLink("Result", "MasterDetails", new { id = item.LabOrders.ORDER_ID },new { @class = "btn btn-primary" , target = "_blank" })</td>
            <td>@Html.ActionLink("Invoice", "Index", "Invoice", new { id = item.LabOrders.ORDER_ID }, new { @class = "btn btn-primary", target = "_blank" })</td>
            @if (item.LabCultureResults?.FirstOrDefault()?.TESTID)
            {
           <!--Here is two (Do not render if TESTID has not a value)-->
                <td>@Html.ActionLink("Culture Result", "download_culture", new { id = item.LabOrders.ORDER_ID, testid = item.LabCultureResults.FirstOrDefault().TESTID }, new { @class = "btn btn-primary", target = "_blank" })</td>
            }
            @*<td>@Html.ActionLink("Culture Result", "download_culture", new { id = item.LabOrders.ORDER_ID,testid = item.LabCultureResults.FirstOrDefault().TESTID }, new { @class = "btn btn-primary", target = "_blank" })</td>*@
        </tr>

        
        }
</table>

當我添加 TESTID 時，此行出現錯誤

<td>@item.LabCultureResults.FirstOrDefault().TESTID</td>

如果可用，如何顯示 TESTID 并在 null 時跳過？

這是控制器代碼：

 public ActionResult Clinicsorders(DateTime? startdate,DateTime? enddate, string pcfileno, string idno , string Passport , string Mobile)
        {

            int custId = (int)Session["UserCustid"];
            
            // eager load navigation properties
            // query is IQueryable
            var query = db.Lab_Orders.Where(r => r.CUSTID == custId)
                .Join(db.Lab_Sample_status, order => order.order_status, status => status.status_id, (order, status) => new { Order = order, Status = status })
                .Join(db.Patients, rec => rec.Order.patient_no, patient => patient.Patient_No, (rec, patient) => new Orders_Tables { LabOrders = rec.Order, LabOrderStatus = rec.Status, patients = patient });


            if (startdate.HasValue && enddate.HasValue)
            {
                query = query.Where(r => DbFunctions.TruncateTime(r.LabOrders.ORDER_DATE) >= DbFunctions.TruncateTime(startdate.Value) &&
                    DbFunctions.TruncateTime(r.LabOrders.ORDER_DATE) <= DbFunctions.TruncateTime(enddate.Value));
            }

            if (!string.IsNullOrEmpty(pcfileno))
            {
                query = query.Where(r => r.patients.PCfileNO == pcfileno);
            }

            if (!string.IsNullOrEmpty(idno))
            {
                query = query.Where(r => r.patients.Patient_id == idno);
            }

         
            var model = query.OrderByDescending(r=>r.LabOrders.ORDER_ID).ToList();

            return View(model);
}

我需要對控制器代碼進行更改并添加表，訂單表類包括一個模型中的所有表

uj5u.com熱心網友回復：

我在您的代碼中發現了另一個問題。您的頁面中有兩個訪問器TESTID。他們在下面的代碼上做了標記。您必須處理這兩個訪問器。可能是你的item或者LabOrders是null。如果沒有，下面的代碼可以完成這項作業。

如果條件取決于它自己的型別。

例如，如果TESTID是 int？你可以使用這個：

item.LabCultureResults?.FirstOrDefault()?.TESTID.HasValue

<table class="table">
    <tr>
        <td> Patient Name </td>
        <td> Order No. </td>
        <td> Test Id</td>
        <td> order date    </td>
        <td> Polyclinic File </td>
        <td> Order Status   </td>


    </tr>
    @foreach (var item in Model)
    {
        <tr>
            <td>@item.patients.Patient_Name</td>
            <td>@item.LabOrders.ORDER_ID</td>
            <!--Here is one-->
            <td>@(item.LabCultureResults?.FirstOrDefault()?.TESTID.HasValue ? item.LabCultureResults?.FirstOrDefault()?.TESTID : "No Test ID" )</td>
            <td>@item.LabOrders.ORDER_DATE</td>
            <td>@item.patients.PCfileNO</td>
            <td>@item.LabOrderStatus.status_name</td>
            <td>@Html.ActionLink("Result", "MasterDetails", new { id = item.LabOrders.ORDER_ID },new { @class = "btn btn-primary" , target = "_blank" })</td>
            <td>@Html.ActionLink("Invoice", "Index", "Invoice", new { id = item.LabOrders.ORDER_ID }, new { @class = "btn btn-primary", target = "_blank" })</td>
            @if(item.LabCultureResults?.FirstOrDefault()?.TESTID.HasValue) 
            {
           <!--Here is two (Do not render if TESTID has not a value)-->
           <td>@Html.ActionLink("Culture Result", "download_culture", new { id = item.LabOrders.ORDER_ID,testid = item.LabCultureResults.FirstOrDefault().TESTID }, new { @class = "btn btn-primary", target = "_blank" })</td>
            }
       </tr>
</table>

uj5u.com熱心網友回復：

FirstOrDefault 如果不存在則回傳..default，因此取消參考將生成空參考例外

編輯：如果 TESTID 不存在則額外

@item.LabCultureResults.FirstOrDefault().TESTID ?? “空的”

快速解決方法是使用空合并運算子 (?)

@item.LabCultureResults.FirstOrDefault()?.TESTID ?? "EMPTY"

或者

@item.LabCultureResults.FirstOrDefault() ?? "EMPTY"

uj5u.com熱心網友回復：

以上答案的組合：

嘗試： @item?.LabCultureResults.FirstOrDefault()?.TESTID ?? ""

uj5u.com熱心網友回復：

演示問題的示例代碼：

List<string> LabCultureResults = null;

Console.WriteLine(LabCultureResults.Count); // (1)
Console.WriteLine(LabCultureResults.FirstOrDefault()); // (2)

(1) 拋出臭名昭著的 NullReferenceException（“物件參考未設定為物件的實體。”）。

(2) 拋出帶有訊息“Value cannot be null. (Parameter 'source')”的 ArgumentNullException，因為可以對 null 值呼叫擴展方法（如 FirstOrDefault），但可能決定不接受它。

所以你的 LabCultureResults 是null.

當該模型是物體框架查詢的結果時，您需要.Include(it => it.LabCultureResults).

請注意，它FirstOrDefault()可能會回傳 a null，因此不要只獲取結果的 TESTID - 當結果為 null 時會拋出 NullReferenceException 。所以使用item.LabCultureResults?.FirstOrDefault()?.TESTID.

轉載請註明出處，本文鏈接：https://www.uj5u.com/yidong/515589.html

標籤：C＃asp.net-mvc

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