c# - 在 Entity Framework 中创建递归实体的正确方法是什么？

Question

我目前正在使用 VS 2010 RC，我正在尝试创建一个包含递归自引用实体的模型。目前，当我从模型中导入实体时，我收到一条错误消息，指出父属性不能成为关联的一部分，因为它被设置为“计算”或“身份”，但我不确定为什么这样做。我一直在手动编辑文件以解决该错误，但模型根本不起作用。

让递归实体在 Entity Framework 中工作的正确方法是什么。

默认导入的模型不起作用。我尝试了几次调整，但每次都得到不同类型的错误。在这一点上，我正在寻找一个解决方案，并解释为什么该解决方案是正确的。

相关数据库对象

CREATE TABLE [dbo].[Appointments](
    [AppointmentId] [int] IDENTITY(1,1) NOT NULL,
    [Description] [nvarchar](1024) NULL,
    [Start] [datetime] NOT NULL,
    [End] [datetime] NOT NULL,
    [Username] [varchar](50) NOT NULL,
    [RecurrenceRule] [nvarchar](1024) NULL,
    [RecurrenceState] [varchar](20) NULL,
    [RecurrenceParentId] [int] NULL,
    [Annotations] [nvarchar](50) NULL,
    [Application] [nvarchar](100) NOT NULL,
    CONSTRAINT [PK_Appointments] PRIMARY KEY CLUSTERED 
    (
        [AppointmentId] ASC
    )
)
GO

ALTER TABLE [dbo].[Appointments]  WITH CHECK ADD  CONSTRAINT [FK_Appointments_ParentAppointments] FOREIGN KEY([RecurrenceParentId])
REFERENCES [dbo].[Appointments] ([AppointmentId])
GO

ALTER TABLE [dbo].[Appointments] CHECK CONSTRAINT [FK_Appointments_ParentAppointments]
GO
EDMX

--

<Schema Namespace="SafetyTrackerModel.Store" Alias="Self" Provider="System.Data.SqlClient" ProviderManifestToken="2005" xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" xmlns="http://schemas.microsoft.com/ado/2006/04/edm/ssdl">
    <EntityContainer Name="SafetyTrackerModelStoreContainer">
      <EntitySet Name="Appointments" EntityType="SafetyTrackerModel.Store.Appointments" store:Type="Tables" Schema="dbo" />
      <AssociationSet Name="FK_Appointments_ParentAppointments" Association="SafetyTrackerModel.Store.FK_Appointments_ParentAppointments">
        <End Role="Appointments" EntitySet="Appointments" />
        <End Role="Appointments1" EntitySet="Appointments" />
      </AssociationSet>
    </EntityContainer>
    <EntityType Name="Appointments">
      <Key>
        <PropertyRef Name="AppointmentId" />
      </Key>
      <Property Name="AppointmentId" Type="int" Nullable="false" StoreGeneratedPattern="Identity" />
      <Property Name="Description" Type="nvarchar" MaxLength="1024" />
      <Property Name="Start" Type="datetime" Nullable="false" />
      <Property Name="End" Type="datetime" Nullable="false" />
      <Property Name="Username" Type="varchar" Nullable="false" MaxLength="50" />
      <Property Name="RecurrenceRule" Type="nvarchar" MaxLength="1024" />
      <Property Name="RecurrenceState" Type="varchar" MaxLength="20" />
      <Property Name="RecurrenceParentId" Type="int" StoreGeneratedPattern="Identity" />
      <Property Name="Annotations" Type="nvarchar" MaxLength="50" />
      <Property Name="Application" Type="nvarchar" Nullable="false" MaxLength="100" />
    </EntityType>
    <Association Name="FK_Appointments_ParentAppointments">
      <End Role="Appointments" Type="SafetyTrackerModel.Store.Appointments" Multiplicity="0..1" />
      <End Role="Appointments1" Type="SafetyTrackerModel.Store.Appointments" Multiplicity="*" />
      <ReferentialConstraint>
        <Principal Role="Appointments">
          <PropertyRef Name="AppointmentId" />
        </Principal>
        <Dependent Role="Appointments1">
          <PropertyRef Name="RecurrenceParentId" />
        </Dependent>
      </ReferentialConstraint>
    </Association>
  </Schema></edmx:StorageModels>
<edmx:ConceptualModels>
  <Schema Namespace="SafetyTrackerModel" Alias="Self" xmlns="http://schemas.microsoft.com/ado/2006/04/edm">
    <EntityContainer Name="SafetyTrackerEntities">
      <EntitySet Name="Appointments" EntityType="SafetyTrackerModel.Appointment" />
      <AssociationSet Name="FK_Appointments_ParentAppointments" Association="SafetyTrackerModel.FK_Appointments_ParentAppointments">
        <End EntitySet="Appointments" Role="Appointment" />
        <End EntitySet="Appointments" Role="Appointment1" />
      </AssociationSet>
      </EntityContainer>
    <EntityType Name="Appointment">
      <Key>
        <PropertyRef Name="AppointmentId" />
      </Key>
      <Property xmlns:a="http://schemas.microsoft.com/ado/2009/02/edm/annotation" Name="AppointmentId" Nullable="false" a:StoreGeneratedPattern="Identity" Type="Int32" />
      <Property Name="Description" MaxLength="1024" FixedLength="false" Unicode="true" Type="String" />
      <Property Name="Start" Nullable="false" Type="DateTime" />
      <Property Name="End" Nullable="false" Type="DateTime" />
      <Property Name="Username" Nullable="false" MaxLength="50" FixedLength="false" Unicode="false" Type="String" />
      <Property Name="RecurrenceRule" MaxLength="1024" FixedLength="false" Unicode="true" Type="String" />
      <Property Name="RecurrenceState" MaxLength="20" FixedLength="false" Unicode="false" Type="String" />
      <Property Name="Annotations" MaxLength="50" FixedLength="false" Unicode="true" Type="String" />
      <Property Name="Application" Nullable="false" MaxLength="100" FixedLength="false" Unicode="true" Type="String" />
      <NavigationProperty Name="ChildAppointments" Relationship="SafetyTrackerModel.FK_Appointments_ParentAppointments" FromRole="Appointment" ToRole="Appointment1" />
      <NavigationProperty Name="ParentAppointment" Relationship="SafetyTrackerModel.FK_Appointments_ParentAppointments" FromRole="Appointment1" ToRole="Appointment" />
    </EntityType>
    </Schema>
</edmx:ConceptualModels>
<edmx:Mappings>
  <Mapping Space="C-S" xmlns="urn:schemas-microsoft-com:windows:storage:mapping:CS">
    <EntityContainerMapping StorageEntityContainer="SafetyTrackerModelStoreContainer" CdmEntityContainer="SafetyTrackerEntities">
      <EntitySetMapping Name="Appointments">
        <EntityTypeMapping TypeName="SafetyTrackerModel.Appointment">
          <MappingFragment StoreEntitySet="Appointments"> <!-- [1] -->
            <ScalarProperty Name="Application" ColumnName="Application" />
            <ScalarProperty Name="Annotations" ColumnName="Annotations" />
            <ScalarProperty Name="RecurrenceState" ColumnName="RecurrenceState" />
            <ScalarProperty Name="RecurrenceRule" ColumnName="RecurrenceRule" />
            <ScalarProperty Name="Username" ColumnName="Username" />
            <ScalarProperty Name="End" ColumnName="End" />
            <ScalarProperty Name="Start" ColumnName="Start" />
            <ScalarProperty Name="Description" ColumnName="Description" />
            <ScalarProperty Name="AppointmentId" ColumnName="AppointmentId" />
          </MappingFragment>
        </EntityTypeMapping>
      </EntitySetMapping>
      <AssociationSetMapping Name="FK_Appointments_ParentAppointments" TypeName="SafetyTrackerModel.FK_Appointments_ParentAppointments" StoreEntitySet="Appointments">
        <EndProperty Name="Appointment1">
          <ScalarProperty Name="AppointmentId" ColumnName="AppointmentId" />
        </EndProperty>
        <EndProperty Name="Appointment">
          <ScalarProperty Name="AppointmentId" ColumnName="RecurrenceParentId" />
        </EndProperty>
        <Condition ColumnName="AppointmentId" IsNull="false" /> <!-- Problem Here -->
      </AssociationSetMapping>
      </EntityContainerMapping>
  </Mapping>
</edmx:Mappings>

因为我得到了编译器错误:

无法为列成员 'AppointmentId' 指定条件，因为它标有 'Computed' 或 'Identity' StoreGeneratedPattern。

如果删除该错误就会消失，但会简单地引入另一个错误:

从第 3350、3380 行开始的映射片段存在问题:EntityTypes SafetyTrackerModel.Appointment 被映射到表 Appointments 中的相同行。映射条件可以用来区分这些类型映射到的行。

恰好是上面标记为 [1] 的行。

此时我不知道我应该做什么。我尝试了很多很多东西，最终我用尽了所有可以尝试的智能东西，并进入了 cargo 狂热之地。

我真的很想了解这里的问题是什么。

Answer 1

EF 可以支持递归对象。您只需导入模型，EF 就会选择关系并允许您进行递归。

参见 MSDN .

关于您的 FK，我不明白您为什么有 CHECK CONSTRAINT。添加 FK 应该是这样的:

ALTER TABLE Appointments
ADD FOREIGN KEY (RecurrenceParentId) REFERENCES Appointments(AppointmentId);

也许您的 FK 创建出了点问题，EF 无法处理？

希望对您有所帮助!

编辑:哈哈，刚看到它是 9 个月前被问到的......好吧，没关系:)