实体框架：模型优先，继承？答案

【问题标题】：Entity Framework: Model First, Inheritance?实体框架：模型优先，继承？
【发布时间】：2011-05-29 17:39:30
【问题描述】：

我有一个 Person 表、一个 Employee 表和一个 Contractor 表。所有员工都是人，所有承包商都是人，每个人要么是雇员，要么是承包商。像这样：

如何使用 Model First 来实现这个概念？继承？

【问题讨论】：

嘿，那张照片看起来很眼熟！ :)
:P 你知道的！我偷了你的句子……再好不过了。
一切都好。我希望你能得到一些答案。祝你好运！

标签： .net entity-framework inheritance ef-model-first

【解决方案1】：

您有三个选择：

1 - 逐表层次结构：有利于性能，因为需要一张物理表。您需要将 discriminator 字段添加到 Person - 例如“PersonType”。这种方法的问题（我发现的）是你最终会有很多可为空的字段，并且派生类型之间的导航属性很困难（根据我的经验）。

2 - 按表格类型：需要单独的表，但如果您想要另一个“人”类型，则可以提高灵活性。

3 - Table-Per Concrete Type：没有这方面的经验，所以不能真正评论它。 AFAIK 它与 TPT 非常相似。

我可能会选择 TPT，只是因为它更容易 IMO。

话虽如此，“Contractor”和“Employee”表中的字段属于同一类型，因此您可以将其概括为带有 TPH 的单个字段。但我猜这不是完整的模型。

模型优先的步骤：

将这三个实体添加到空白 EDMX。
将“人物”标记为摘要
将“Contractor”和“Employee”设置为派生自“Person”。（添加 -> 继承）
从“Employee”和“Contractor”实体中删除 ID 字段（不是必需的，它将从“Person”继承 ID）。
从模型生成数据库。

【讨论】：

【解决方案2】：

那个表结构 + 继承 == TPT。在设计器中，它看起来像这样：

...以及实体的原始 EDMX 以及到这些表的映射：

<?xml version="1.0" encoding="utf-8"?>
<edmx:Edmx Version="2.0" xmlns:edmx="http://schemas.microsoft.com/ado/2008/10/edmx" xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" xmlns:ssdl="http://schemas.microsoft.com/ado/2009/02/edm/ssdl" xmlns:edm="http://schemas.microsoft.com/ado/2008/09/edm" xmlns:annotation="http://schemas.microsoft.com/ado/2009/02/edm/annotation" xmlns:map="http://schemas.microsoft.com/ado/2008/09/mapping/cs" xmlns:codegen="http://schemas.microsoft.com/ado/2006/04/codegeneration" xmlns:huagati="http://www.huagati.com/edmxtools/annotations">
  <!--Updated by Huagati EDMX Tools version 2.16.4007.30259 on 2010-12-23 09:13:27-->
  <!-- EF Runtime content -->
  <edmx:Runtime>
    <!-- SSDL content -->
    <edmx:StorageModels>
      <Schema xmlns="http://schemas.microsoft.com/ado/2009/02/edm/ssdl" Namespace="Model1.Store" Alias="Self" Provider="System.Data.SqlClient" ProviderManifestToken="2008">
        <EntityContainer Name="Model1TargetContainer">
          <EntitySet Name="Person" store:Type="Tables" Schema="dbo" Table="Person" store:Name="Person" EntityType="Model1.Store.Person" />
          <EntitySet Name="Employee" store:Type="Tables" Schema="dbo" Table="Employee" store:Name="Employee" EntityType="Model1.Store.Employee" />
          <AssociationSet Name="FK_Employee_Person" Association="Model1.Store.FK_Employee_Person">
            <End Role="Person" EntitySet="Person" />
            <End Role="Employee" EntitySet="Employee" />
          </AssociationSet>
          <EntitySet Name="Contractor" store:Type="Tables" Schema="dbo" Table="Contractor" store:Name="Contractor" EntityType="Model1.Store.Contractor" />
          <AssociationSet Name="FK_Contractor_Person" Association="Model1.Store.FK_Contractor_Person">
            <End Role="Person" EntitySet="Person" />
            <End Role="Contractor" EntitySet="Contractor" />
          </AssociationSet>
        </EntityContainer>
        <EntityType Name="Person">
          <Documentation />
          <Key>
            <PropertyRef Name="PersonId" />
          </Key>
          <Property Name="PersonId" Type="bigint" Nullable="false" StoreGeneratedPattern="Identity" />
          <Property Name="Name" Type="nvarchar" Nullable="true" MaxLength="50" />
        </EntityType>
        <EntityType Name="Employee">
          <Documentation />
          <Key>
            <PropertyRef Name="EmployeeId" />
          </Key>
          <Property Name="EmployeeId" Type="bigint" Nullable="false" />
          <Property Name="EmployeeNumber" Type="nvarchar" Nullable="true" MaxLength="50" />
        </EntityType>
        <Association Name="FK_Employee_Person">
          <End Multiplicity="1" Role="Person" Type="Model1.Store.Person" />
          <End Multiplicity="0..1" Role="Employee" Type="Model1.Store.Employee" />
          <ReferentialConstraint>
            <Principal Role="Person">
              <PropertyRef Name="PersonId" />
            </Principal>
            <Dependent Role="Employee">
              <PropertyRef Name="EmployeeId" />
            </Dependent>
          </ReferentialConstraint>
        </Association>
        <EntityType Name="Contractor">
          <Documentation />
          <Key>
            <PropertyRef Name="ContractorId" />
          </Key>
          <Property Name="ContractorId" Type="bigint" Nullable="false" />
          <Property Name="ContractorNumber" Type="nvarchar" Nullable="true" MaxLength="50" />
        </EntityType>
        <Association Name="FK_Contractor_Person">
          <End Multiplicity="1" Role="Person" Type="Model1.Store.Person" />
          <End Multiplicity="0..1" Role="Contractor" Type="Model1.Store.Contractor" />
          <ReferentialConstraint>
            <Principal Role="Person">
              <PropertyRef Name="PersonId" />
            </Principal>
            <Dependent Role="Contractor">
              <PropertyRef Name="ContractorId" />
            </Dependent>
          </ReferentialConstraint>
        </Association>
      </Schema>
    </edmx:StorageModels>
    <!-- CSDL content -->
    <edmx:ConceptualModels>
      <Schema xmlns="http://schemas.microsoft.com/ado/2008/09/edm" xmlns:cg="http://schemas.microsoft.com/ado/2006/04/codegeneration" xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" Namespace="Model1" Alias="Self" xmlns:annotation="http://schemas.microsoft.com/ado/2009/02/edm/annotation">
        <EntityContainer Name="Model1Container" annotation:LazyLoadingEnabled="true">
          <EntitySet Name="Person" EntityType="Model1.Person" huagati:InheritanceStrategy="TPT" />
        </EntityContainer>
        <EntityType Name="Person">
          <Key>
            <PropertyRef Name="PersonId" />
          </Key>
          <Property Type="Int64" Name="PersonId" Nullable="false" annotation:StoreGeneratedPattern="Identity" />
          <Property Type="String" Name="Name" Unicode="true" MaxLength="50" Nullable="true" />
        </EntityType>
        <EntityType Name="Employee" BaseType="Model1.Person">
          <Property Type="String" Name="EmployeeNumber" Unicode="true" MaxLength="50" Nullable="true" />
        </EntityType>
        <EntityType Name="Contractor" BaseType="Model1.Person">
          <Property Type="String" Name="ContractorNumber" Nullable="true" Unicode="true" MaxLength="50" />
        </EntityType>
      </Schema>
    </edmx:ConceptualModels>
    <!-- C-S mapping content -->
    <edmx:Mappings>
      <Mapping xmlns="http://schemas.microsoft.com/ado/2008/09/mapping/cs" Space="C-S">
        <Alias Key="Model" Value="Model1" />
        <Alias Key="Target" Value="Model1.Store" />
        <EntityContainerMapping CdmEntityContainer="Model1Container" StorageEntityContainer="Model1TargetContainer">
          <EntitySetMapping Name="Person">
            <EntityTypeMapping TypeName="IsTypeOf(Model1.Person)">
              <MappingFragment StoreEntitySet="Person">
                <ScalarProperty Name="PersonId" ColumnName="PersonId" />
                <ScalarProperty Name="Name" ColumnName="Name" />
              </MappingFragment>
            </EntityTypeMapping>
            <EntityTypeMapping TypeName="IsTypeOf(Model1.Employee)">
              <MappingFragment StoreEntitySet="Employee">
                <ScalarProperty Name="PersonId" ColumnName="EmployeeId" />
                <ScalarProperty Name="EmployeeNumber" ColumnName="EmployeeNumber" />
              </MappingFragment>
            </EntityTypeMapping>
            <EntityTypeMapping TypeName="IsTypeOf(Model1.Contractor)">
              <MappingFragment StoreEntitySet="Contractor">
                <ScalarProperty Name="PersonId" ColumnName="ContractorId" />
                <ScalarProperty Name="ContractorNumber" ColumnName="ContractorNumber" />
              </MappingFragment>
            </EntityTypeMapping>
          </EntitySetMapping>
        </EntityContainerMapping>
      </Mapping>
    </edmx:Mappings>
  </edmx:Runtime>
  <!-- EF Designer content (DO NOT EDIT MANUALLY BELOW HERE) -->
  <edmx:Designer xmlns="http://schemas.microsoft.com/ado/2008/10/edmx">
    <edmx:Connection>
      <DesignerInfoPropertySet>
        <DesignerProperty Name="MetadataArtifactProcessing" Value="EmbedInOutputAssembly" />
      </DesignerInfoPropertySet>
    </edmx:Connection>
    <edmx:Options>
      <DesignerInfoPropertySet>
        <DesignerProperty Name="ValidateOnBuild" Value="true" />
        <DesignerProperty Name="EnablePluralization" Value="True" />
      </DesignerInfoPropertySet>
    </edmx:Options>
    <!-- Diagram content (shape and connector positions) -->
    <edmx:Diagrams>
      <Diagram Name="Model1">
        <EntityTypeShape EntityType="Model1.Person" Width="1.5" PointX="5.125" PointY="2.125" Height="1.4033821614583331" />
        <EntityTypeShape EntityType="Model1.Employee" Width="1.5" PointX="3.875" PointY="4" Height="1.2110807291666665" />
        <InheritanceConnector EntityType="Model1.Employee">
          <ConnectorPoint PointX="5.875" PointY="3.5283821614583331" />
          <ConnectorPoint PointX="5.875" PointY="3.76" />
          <ConnectorPoint PointX="4.625" PointY="3.76" />
          <ConnectorPoint PointX="4.625" PointY="4" />
        </InheritanceConnector>
        <EntityTypeShape EntityType="Model1.Contractor" Width="2" PointX="5.875" PointY="4" Height="1.2110807291666665" />
        <InheritanceConnector EntityType="Model1.Contractor" ManuallyRouted="false">
          <ConnectorPoint PointX="5.875" PointY="3.5283821614583331" />
          <ConnectorPoint PointX="5.875" PointY="3.76" />
          <ConnectorPoint PointX="6.875" PointY="3.76" />
          <ConnectorPoint PointX="6.875" PointY="4" />
        </InheritanceConnector>
      </Diagram>
    </edmx:Diagrams>
  </edmx:Designer>
</edmx:Edmx>

有关不同继承类型的更详细说明以及它们与物理数据库表的关系，请参阅：
http://huagati.blogspot.com/2010/10/mixing-inheritance-strategies-in-entity.html
...和...
http://blogs.msdn.com/b/adonet/archive/2010/10/25/inheritance-mapping-a-walkthrough-guide-for-beginners.aspx

【讨论】：