SqlNullValueException：Json 调用时数据为 Null

Question

我已经看到了一些关于此的主题，但似乎对我的情况没有帮助。我正在（使用 EF）查询 POCO 对象，然后尝试在 MVC 项目中通过 Json 返回结果。

我的控制器返回一个 JsonResult，我的控制器的最后两行如下所示：

var results = _context.Churches.Include(c => c.Address).Include(c => c.Address.Country).Where(predicate).ToList();
return Json(results, JsonRequestBehavior.AllowGet);

错误发生在调用 Json() 的第二行。但是，我无法知道是什么财产导致了这个问题。我在通话前查看了结果列表，一切看起来都很好。肯定有 null 属性，但没有一个是必需的。

我将在下面包含错误输出（尽管它的格式不正确）。究竟是什么导致了这个问题似乎不是很明显——我怎样才能找出问题出在哪里？

错误文字

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Data.SqlTypes.SqlNullValueException: Data is Null. This method or property cannot be called on Null values.
at System.Data.SqlTypes.SqlDouble.get_Value()
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeCustomObject(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeCustomObject(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeCustomObject(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeCustomObject(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeCustomObject(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeEnumerable(IEnumerable enumerable, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValue(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, SerializationFormat serializationFormat)
at System.Web.Mvc.JsonResult.ExecuteResult(ControllerContext context)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<InvokeActionResultWithFilters>b__19()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)

这是我的 POCO 模型：

    public class Church : IUserTrackingEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
    [Display(Name="Denomination")]
    public int? DenominationId { get; set; }
    public Denomination Denomination { get; set; }
    [Display(Name="Web Address")]
    public string WebAddress { get; set; }
    public string Contact { get; set; }
    [Display(Name="Position")]
    public int? ContactPositionId { get; set; }
    public ContactPosition ContactPosition { get; set; }
    [Display(Name="Email")]
    public string EmailAddress { get; set; }
    [Display(Name="Phone Number")]
    public string PhoneNumber { get; set; }
    [Display(Name="Ext.")]
    public string PhoneExtension { get; set; }
    [Display(Name="Phone Type")]
    public int? PhoneNumberTypeId { get; set; }
    [Display(Name = "Country")]
    public int? CountryId { get; set; }
    public Country Country { get; set; }
    [Display(Name = "Partnership Requested")]
    public DateTime? PartnershipRequestDate { get; set; }
    [Display(Name = "Partnership Accepted")]
    public DateTime? PartnershipAcceptDate { get; set; }
    [Display(Name = "Last Contacted")]
    public DateTime? LastContactDate { get; set; }
    public string Notes { get; set; }
    public string LastChangedBy { get; set; }
    public int? AddressId { get; set; }
    public Address Address { get; set; }
}
    public class Country
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Continent { get; set; }
    public string PostalCodeFormat { get; set; }
    public string PostalCodeRegex { get; set; }
    public string Citizenship { get; set; }
    public string NTMCode { get; set; }
    public string ISOCode { get; set; }
    public string ISO3Code { get; set; }
    public string FIPSCode { get; set; }
}
    public class Address : IUserTrackingEntity
{
    public int Id { get; set; }
    public string Addressee { get; set; }
    [Required(ErrorMessage = "A value must be entered into street 1.")]
    public string Street1 { get; set; }
    public string Street2 { get; set; }
    public string Locality { get; set; }
    public string District { get; set; }
    [Required(ErrorMessage="A Country is required.")]
    public int CountryId { get; set; }
    public Country Country { get; set; }
    public string PostalCode { get; set; }
    public bool IsVerified { get; set; }
    public string NTMId { get; set; }
    public string LastChangedBy { get; set; }
    public DbGeography Location { get; set; }

    public double? Longitude
    {
        get
        {
            return Location == null ? null : Location.Longitude;
        }

        set
        {
            if (value != null)
                Location = DbGeography.FromText(String.Format("POINT({0} {1})", value, Latitude ?? 0d), 4326);
        }
    }
    public double? Latitude
    {
        get
        {
            return Location == null ? null : Location.Latitude;
        }

        set
        {
            if (value != null)
                Location = DbGeography.FromText(String.Format("POINT({0} {1})", Longitude ?? 0d, value), 4326);
        }
    }

}

Answer 1

当 JSON 序列化程序尝试序列化 Address.Location 中的 DbGeography 实例时，可能会引发异常。该实例的某些（double-valued 和延迟解析）属性对于该实例表示的位置无效，但序列化程序不知道这一点并继续尝试访问导致异常的该属性。

将[ScriptIgnore] 属性添加到Address.Location 属性应该可以修复它。