实体框架4.1 Ghost列

Question

我目前在使用EF4.1时遇到了一些问题.SQL的生成似乎与我期望基于我的类生成的内容不匹配.我有以下课程(这只是一个较小的一个较大的集合,但是,这是我似乎有问题的地方)...

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; } 
}

当我通过Include方法询问OccurrenceSecurities时,我要求同时包括Occurrence和Person.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.

有谁知道它们来自哪里以及它们为什么存在？

此外,我知道这是一个多对多关系,但是,OccurrenceSecurities表/类将扩展为包含更多数据.

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根据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”。当您查询时，EF 不会使用多个结果集（并非所有后备存储都支持），而是发出具有如下结果的查询A.Include("B.C")：

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，形成 2 A、 3B和 7 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。