Linq强制使用DefaultIfEmpty加载实体给ObjectDisposedException

Question

我有这个linq：

using (PlantContext context = ContextManager.GetPlantContext(plantId.PlantPath))
        {
            results = (from p in context.Plants
                       join subplant in context.Subplants on p.Id equals subplant.PlantId
                       join inverter in context.Inverters on subplant.Id equals inverter.SubplantId
                       join inverterActualData in context.InverterActualDatas on inverter.Id equals inverterActualData.InverterId into joinAll
                       from joinItem in joinAll.DefaultIfEmpty()
                       select new
                       {
                           ActualData = joinItem,
                           Inverter = inverter,
                           Subplant = subplant,
                           Plant = p
                       }).AsEnumerable().Select(r => r.Inverter).ToList();
        }

之后，我要查看结果：

foreach (Inverter inverter in results)
{
     if (inverter.InverterActualData == null)
     {
     }
}

这会在“ if（inverter.InverterActualData == null）”行上引发以下异常：

An exception of type 'System.ObjectDisposedException' occurred in System.Data.Entity.dll but was not handled in user code

我想做的是获取逆变器列表，但同时加载其Subplant和InverterActualData属性。 （同样，对于Subplant，加载Plant属性）。

当没有针对Inverter的InverterActualData记录时，就会出现此问题。 在这种情况下，将引发异常。

为什么我要在关闭上下文之前加载所有数据？ 因为一次访问数据库要比分别为每个逆变器调用InverterActualData快得多。

如您所见，我正在尝试检查InverterActualData属性是否为null，但显然未加载。 无论如何，都会引发异常。

我也尝试添加：

join inverter in context.Inverters.Include(InverterExtension.Relations.InverterActualData) on subplant.Id equals inverter.SubplantId

但这也不起作用。

对我来说似乎很奇怪，因为在事件探查器中，查询是这样翻译的：

SELECT 1                                    AS [C1],
   [Extent4].[InverterId]               AS [InverterId],
   [Extent4].[Period]                   AS [Period],
   [Extent4].[OperatingHours]           AS [OperatingHours],
   [Extent3].[Id]                       AS [Id],
   [Extent3].[InverterTypeId]           AS [InverterTypeId],
   [Extent3].[SubplantId]               AS [SubplantId],
   [Extent3].[Name]                     AS [Name],
   [Extent2].[Id]                       AS [Id1],
   [Extent2].[PlantId]                  AS [PlantId],
   [Extent2].[Name]                     AS [Name1],
   [Extent1].[Id]                       AS [Id2],
   [Extent1].[Name]                     AS [Name2],
FROM   [Plant] AS [Extent1]
   INNER JOIN [Subplants] AS [Extent2] ON [Extent1].[Id] = [Extent2].[PlantId]
   INNER JOIN [Inverters] AS [Extent3] ON [Extent2].[Id] = [Extent3].[SubplantId]
   LEFT OUTER JOIN [InverterActualData] AS [Extent4] ON [Extent3].[Id] = [Extent4].[InverterId]

这正是我想要的。 另外，在数据库上运行此查询，还会获得Inverter，Subplant和Plant数据以及InverterActualData的默认值。

可能是什么问题呢？

Answer 1

做到了：

using (PlantContext context = ContextManager.GetPlantContext(plantId.PlantPath))
        {
            context.ContextOptions.LazyLoadingEnabled = false;
            results = (from p in context.Plants
                       join subplant in context.Subplants on p.Id equals subplant.PlantId
                       join inverter in context.Inverters on subplant.Id equals inverter.SubplantId
                       join inverterActualData in context.InverterActualDatas on inverter.Id equals inverterActualData.InverterId into joinAll
                       from joinItem in joinAll.DefaultIfEmpty()
                       select new
                       {
                           ActualData = joinItem,
                           Inverter = inverter,
                           Subplant = subplant,
                           Plant = p
                       }).ToList().Select(r => r.Inverter).ToList();
        }

在这里，“ context.ContextOptions.LazyLoadingEnabled = false;” 和第一个“ ToList（）”是必不可少的