实体框架 4.1 幽灵列

Question

我目前在使用 EF4.1 时遇到一些问题。 SQL 的生成似乎与我期望根据我的类生成的内容不匹配。我有以下类（这只是一个较大集合的较小集合，但是，这就是我似乎遇到问题的地方）...

public class CustomEntityContext : DbContext
{
    public CustomEntityContext()
             :base(ConfigurationManager.ConnectionStrings["DBConnection"].ConnectionString) {}

    public DbSet<Person> People { get; set; }
    public DbSet<Occurrence> Occurrences { get; set; }
    public DbSet<OccurrenceSecurity> OccurrenceSecurities { get; set; }
}


[DataContract(IsReference = true)]
[Table("Occurrence")]
public class Occurrence 
{
    [DataMember] public int ID { get; set; }
    [DataMember] public string Number { get; set; }
    [DataMember] public bool? IsMOR { get; set; }
    [DataMember] public bool? IsConfidential { get; set; }
    [DataMember] public int? IncidentID { get; set; }
    [DataMember] public bool? CanPublish { get; set; }
    [DataMember] public bool? IsFeedbackRequired { get; set; }
    [DataMember] public bool? IsRegulatorReport { get; set; }
    [DataMember] public DateTime? RecordedDate { get; set; }
    [DataMember] public DateTime? ReportedDate { get; set; }
    [DataMember] public int? ReportTypeID { get; set; }
    [DataMember] public bool? IsMain { get; set; }
    [DataMember] public bool? IsRejected { get; set; }  
    [DataMember] public string Title { get; set; }
    [DataMember] public byte[] Version { get; set; }
    [DataMember] public string ReportDataXml { get; set; }
    [DataMember] public int? LocationID { get; set; }
    [DataMember, ForeignKey("RecordedByPersonID")] public Person Recorder { get; set; }
    [DataMember, ForeignKey("ReportedByPersonID")] public Person Reporter { get; set; }
}

[DataContract(IsReference = true)]
[Table("OccurrenceSecurity")]
public class OccurrenceSecurity
{
    [DataMember, Key, Column("PersonID", Order = 0)] public int PersonID { get; set; }
    [DataMember, ForeignKey("PersonID")] public Person Person { get; set; }
    [DataMember, Key, Column("OccurrenceID", Order = 1)] public int OccurrenceID { get; set;          
    [DataMember, ForeignKey("OccurrenceID")] public Occurrence Occurrence { get; set; }
}

[DataContract(IsReference = true)]
[Table("Person")]
public class Person 
{
    [DataMember] public int ID { get; set; }
    [DataMember] public string FullName { get; set; }
    //[DataMember] public Occurrence[] RecordedOccurrences { get; set; }
    //[DataMember] public Occurrence[] ReportedOccurrences { get; set; }
    //[DataMember] public OccurrenceSecurity[] OccurrenceSecurities { set; get; } 
}

当我使用 Include 方法请求 OccurrenceSecurities 时，我要求包括事件和人物。随后，生成的 SQL 如下...

SELECT 
[Extent1].[PersonID] AS [PersonID], 
[Extent1].[OccurrenceID] AS [OccurrenceID], 
[Extent2].[ID] AS [ID], 
[Extent2].[FullName] AS [FullName], 
[Extent3].[ID] AS [ID1], 
[Extent3].[Number] AS [Number], 
[Extent3].[IsMOR] AS [IsMOR], 
[Extent3].[IsConfidential] AS [IsConfidential], 
[Extent3].[IncidentID] AS [IncidentID], 
[Extent3].[CanPublish] AS [CanPublish], 
[Extent3].[IsFeedbackRequired] AS [IsFeedbackRequired], 
[Extent3].[IsRegulatorReport] AS [IsRegulatorReport], 
[Extent3].[RecordedByPersonID] AS [RecordedByPersonID], 
[Extent3].[RecordedDate] AS [RecordedDate], 
[Extent3].[ReportedByPersonID] AS [ReportedByPersonID], 
[Extent3].[ReportedDate] AS [ReportedDate], 
[Extent3].[ReportTypeID] AS [ReportTypeID], 
[Extent3].[IsMain] AS [IsMain], 
[Extent3].[IsRejected] AS [IsRejected], 
[Extent3].[Title] AS [Title], 
[Extent3].[Version] AS [Version], 
[Extent3].[ReportDataXml] AS [ReportDataXml], 
[Extent3].[LocationID] AS [LocationID], 
[Extent3].[Person_ID] AS [Person_ID],               -- Where does this come from?
[Extent3].[Person_ID1] AS [Person_ID1]              -- Where does this come from?
FROM   [dbo].[OccurrenceSecurity] AS [Extent1]
INNER JOIN [dbo].[Person] AS [Extent2] ON [Extent1].[PersonID] = [Extent2].[ID]
LEFT OUTER JOIN [dbo].[Occurrence] AS [Extent3] ON [Extent1].[OccurrenceID] = [Extent3].[ID]

如您所见，Select 块末尾有 2 列，分别选择 Person_ID 和 Person_ID1。这些不存在于我的基础表或我的对象中。

有谁知道它们从哪里来以及为什么在那里？

另外，我知道这是一个多对多关系，但是，OccurrenceSecurities 表/类将扩展以容纳更多数据。

谢谢， 大卫

Answer 1

使用 Include 方法，我要求包含 Occurrence 和 Person

EF 将使用这些额外的列从查询结果构建对象图。通过使用 Include，您是在说“我只想执行一个存储命令，但我想检索许多对象”。 EF 不是使用多个结果集（并非所有后备存储都支持），而是在您查询 A.Include("BC") 时发出带有如下结果的查询：

columns for A1 columns for B1 columns for C1
columns for A1 columns for B1 columns for C2
columns for A1 columns for B1 columns for C3
columns for A1 columns for B2 columns for C4
columns for A1 columns for B2 columns for C5
columns for A2 columns for B3 columns for C6
columns for A2 columns for B3 columns for C7

然后将这些行缝合在一起制作两个 A、3 个 B 和 7 个 C，并具有适当的关系。

我猜测，您显示的特定额外列是 EF 在拼接过程中使用的。