EF导航属性包括不加载答案

【问题标题】：EF navigation property include doesn't loadEF导航属性包括不加载
【发布时间】：2014-09-30 13:14:50
【问题描述】：

我正在尝试访问我的RegisterCountLog 上的Register 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，它始终为空。

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）包括Register。该特定位之后的查询又名queryableLogs 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])

它是这样使用的：

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();

除了RegisterName 始终为空之外，一切都运行良好。如果我查看查询 Register 也是空的。为什么加载不出来？

这里是 EF 类

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; }
}

【问题讨论】：

在获取 RegisterCountLog 集合以进行即时加载时，将寄存器设为虚拟以启用延迟加载或使用 .Include(x => x.Register) 方法。
.GetAll() 应该预加载它（我使用存储库模式），我也尝试过使用虚拟但没用..我会再试一次以防万一

标签： c# entity-framework navigation-properties

【解决方案1】：

您可能正在使用即时加载，并且您必须指定 .Include(x => x.Register) 或 .Include("Register")，具体取决于您的 EF 版本

如果您将变量命名为“好”，则可能会出现另一个问题（对于分组的事物，急切加载并不好）。一种方法是在选择某些内容之前枚举查询（列出）。（如果没有性能问题）

编辑：当我阅读您之前的评论时，我真的认为是按问题分组（分组更改您的 linq 结构，并且 include 无法正常工作）

方法是这样的：

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()]

【讨论】：