Question

我正在尝试访问Register上的RegisterCountLog导航属性。由于某种原因，它始终为空。因此，当我尝试访问RegisterName时，它始终为null。

public IQueryable<RegisterCountLog> GetCountsForDevice(long deviceSerial)
{
    return this.ServiceCollection.GetAll(c => c.Register)
               .Where(c => c.DeviceSerial == deviceSerial).AsNoTracking();
}

请注意，ServiceCollection.GetAll()将（或应该）包含Register。该特定位queryableLogs之后的查询是

SELECT 
    [Extent2].[Contribution] AS [Contribution], 
    [Extent1].[DeviceSerial] AS [DeviceSerial], 
    [Extent1].[LogEntryID] AS [LogEntryID], 
    [Extent1].[RegisterId] AS [RegisterId], 
    [Extent1].[Value] AS [Value], 
    [Extent1].[Timestamp] AS [Timestamp], 
    [Extent2].[RegisterId] AS [RegisterId1], 
    [Extent2].[DeviceSerial] AS [DeviceSerial1], 
    [Extent2].[RegisterName] AS [RegisterName], 
    [Extent2].[ZoneEntrance_ZoneEntranceID] AS [ZoneEntrance_ZoneEntranceID]
    FROM  [dbo].[RegisterCountLogs] AS [Extent1]
    INNER JOIN [dbo].[Registers] AS [Extent2] 
          ON  ([Extent1].[RegisterId] = [Extent2].[DeviceSerial]) 
          AND ([Extent1].[DeviceSerial] = [Extent2].[RegisterId])

它的用法如下：

var queryableLogs = countLogService.GetCountsForDevice(serialNumber);
var groupedLogs= gLogs
    .Select(r => new Register
    {
        RegisterId = r.FirstOrDefault().RegisterId,
        RegisterName = r.FirstOrDefault().Register.RegisterName, // Here!
        DeviceSerial = r.FirstOrDefault().DeviceSerial,
        CountLogs = r.GroupBy(rc => 
                              new {Day = SqlFunctions
                                        .DatePart("dy", rc.Timestamp)})
                     .Select(rl => new RegisterCountLog()
                                   {
                                     Value = rl.to FirstOrDefault().Value,
                                     Timestamp = rl.FirstOrDefault()
                                                   .Timestamp,
                                   })
                     .OrderByDescending(l => l.Timestamp)
                     .ToList()
    })
    .Where(r=>r.CountLogs.Count() > 0)
    .OrderByDescending(r => r.RegisterId)
    .ToList();

除RegisterName始终为空之外，一切都很完美。如果我查看查询Register也是null。为什么不加载？

以下是EF课程

public class RegisterCountLog
{
    [Key, Column(Order = 1)]
    [ForeignKey("Register")]
    public long DeviceSerial { get; set; }

    [Key, Column(Order = 2)]
    public long LogEntryID { get; set; }

    [Key, Column(Order = 3)]
    [ForeignKey("Register")]
    public long RegisterId { get; set; }

    public long Value { get; set; }

    public DateTime Timestamp { get; set; }

    public Register Register { get; set; }
}

public class Register
{
    public enum ContributionType
    {
        FlowIn,
        FlowOut
    }

    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    [Key, Column(Order = 1)]
    public long RegisterId { get; set; }

    [Key]
    [ForeignKey("Device"), Column(Order = 2)]
    public long DeviceSerial { get; set; }

    [StringLength(50)]
    public string RegisterName { get; set; }

    public ContributionType Contribution { get; set; }    

    public virtual Device Device { get; set; }
}

Answer 1

您可能正在使用预先加载，但必须指定.Include(x => x.Register)或.Include("Register")，具体取决于您的EF版本

如果你给变量命名很好，可能会有另一个问题（对于分组的东西，急切加载并不是很好）。一种方法是在选择内容之前枚举查询（列表）。（如果没有性能问题）

编辑：当我读到你之前的评论时，我真的认为是按问题分组（通过更改你的linq结构分组并且包括不工作的任何人）

方法是：

var groupedPersons     = db.Appointments
                        .Include_Service()
                        .Include_Location()
                        .Include_Room()
                        .IncludeEhr_Patient()
                        .IncludeEhr_Person()
                        .IncludeEhr_Personal()
                        .ToList() // see that i enumerate before i group by
                        .GroupBy(x => x.PersonId).Select()[.ToList()]

EF导航属性包括不加载

1 个答案: