如何避免 NHibernate 中不必要的连接

Question

我有一个名为“Entity”的类，它可以是个人或组织。我还有一些其他类是 Entity 的后代，它们的属性在我的数据库的扩展表中定义。我的一个后代名叫“用户”。

我的表结构的一个真正被截断的示例：

Table: ENTITY
Id - UniqueIdentifier
LastName - Varchar(200)
FirstName - Varchar(50)

Table: USER
Id - UniqueIdentifier (FK to Entity)
Password - Varchar(20)

使用 NHibernate.Linq，我获取一个非用户实体的实例，如下所示：

Session.Get<Entity>(myIdValue);

生成的 SQL 始终连接扩展表并包含在扩展表中找到的附加列。

当我请求 Entity 的一个实例时，我真的不想要它的后代之一。

谁能指出我的错误吗？

根据大众的需求，这是我引用的实体类层次结构的映射文件：

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true">
  <!-- AbstractEntity -->
  <class xmlns="urn:nhibernate-mapping-2.2" name="netfile.model.filer.entities.AbstractEntity, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="Entity" abstract="true" discriminator-value="AbstractEntity">
    <id name="Id" type="System.Guid">
      <column name="Id" />
      <generator class="guid.comb" />
    </id>
    <discriminator column="Type" type="string"/>
    <property name="Xref">
      <column name="Xref" />
    </property>
    <property name="Name">
      <column name="LastName" />
    </property>
    <property name="FiledAs">
      <column name="FiledAs" />
    </property>
    <property name="RestKey">
      <column name="RestKey" />
    </property>
    <property name="SearchText">
      <column name="SearchText" />
    </property>
    <many-to-one class="netfile.model.filer.dataspaces.Dataspace, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="Dataspace">
      <column name="Dataspace_id" />
    </many-to-one>
    <many-to-one class="netfile.model.filer.Ownership, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="Ownership">
      <column name="Ownership_id" />
    </many-to-one>
    <bag name="Descriptions" cascade="all-delete-orphan" inverse="true">
      <key>
        <column name="Entity_Id" />
      </key>
      <one-to-many class="netfile.model.filer.descriptions.AbstractDescription" />
    </bag>
    <!-- All Concrete Entity Types (Org, Ind, etc) -->
    <subclass name="netfile.model.filer.entities.Entity, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="Entity">
      <property name="FirstName">
        <column name="FirstName" />
      </property>
      <property name="IsIndividual">
        <column name="IsIndividual" />
      </property>
      <property name="IsLobbyistClient">
        <column name="IsLobbyistClient" />
      </property>
      <property name="MiddleName">
        <column name="MiddleName" />
      </property>
      <property name="Prefix">
        <column name="Prefix" />
      </property>
      <property name="Suffix">
        <column name="Suffix" />
      </property>
      <property name="Occupation">
        <column name="Occupation" />
      </property>
      <bag name="ContactMethods" cascade="all" inverse="true">
        <key>
          <column name="Entity_Id" />
        </key>
        <one-to-many class="netfile.model.common.OneLineAddress, netfile.model.common, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
      </bag>
      <many-to-one cascade="all" class="netfile.model.common.AddressUS, netfile.model.common, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="BusinessAddress">
        <column name="BusinessAddress_id" />
      </many-to-one>
      <many-to-one cascade="all" class="netfile.model.common.AddressUS, netfile.model.common, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="MailingAddress">
        <column name="MailingAddress_id" />
      </many-to-one>
      <many-to-one cascade="all" class="netfile.model.common.AddressUS, netfile.model.common, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="DisclosureAddress">
        <column name="DisclosureAddress_id" />
      </many-to-one>
      <many-to-one class="netfile.model.filer.entities.Entity, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="Employer">
        <column name="Employer_id" />
      </many-to-one>
      <!-- Organization, Agency -->
      <!-- Agency -->
      <subclass name="netfile.model.filer.entities.Agency, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="Agency">
        <join table="Entity_Agency">
          <key>
            <column name="Entity_id" />
          </key>
          <property name="Abbreviation">
            <column name="Abbreviation" />
          </property>
          <many-to-one cascade="save-update" class="netfile.model.filer.entities.Entity, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="TechnicalSupportContact">
            <column name="TechnicalSupportContact_id" />
          </many-to-one>
        </join>
      </subclass>
      <!-- Committee -->
      <subclass name="netfile.model.filer.entities.campaign.Committee, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="Committee">
        <join table="Entity_Committee">
          <key>
            <column name="Entity_id" />
          </key>
          <property name="FilerId">
            <column name="FilerId" />
          </property>
        </join>
        <!-- GeneralPurposeCommittee -->
        <subclass name="netfile.model.filer.entities.campaign.GeneralPurposeCommittee, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="GeneralPurposeCommittee">
        </subclass>
        <!-- ControlledCommittee -->
        <subclass name="netfile.model.filer.entities.campaign.ControlledCommittee, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="ControlledCommittee">
          <bag name="ControllingOfficers" table="Entity_Links">
            <key>
              <column name="Source_Id" not-null="true"/>
            </key>
            <many-to-many class="netfile.model.filer.entities.Entity, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
              <column name="Target_Id" not-null="true"/>
            </many-to-many>
          </bag>
          <!-- PrincipalCampaignCommittee -->
          <subclass name="netfile.model.filer.entities.campaign.PrincipalCampaignCommittee, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="PrincipalCampaignCommittee">
          </subclass>
        </subclass>
      </subclass>
      <!-- User -->
      <subclass name="netfile.model.filer.entities.User, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="User">
        <join table="Entity_User">
          <key>
            <column name="Entity_id" />
          </key>
          <property name="ChallengeAnswer">
            <column name="ChallengeAnswer" />
          </property>
          <property name="ChallengeQuestion">
            <column name="ChallengeQuestion" />
          </property>
          <property name="Disabled">
            <column name="Disabled" />
          </property>
          <property name="Password">
            <column name="Password" />
          </property>
          <property name="PasswordResetKey">
            <column name="PasswordResetKey" />
          </property>
          <property name="Reference">
            <column name="Reference" />
          </property>
          <property name="SecurityLocked">
            <column name="SecurityLocked" />
          </property>
          <bag name="DataspacePermissions" cascade="all">
            <key>
              <column name="User_Id" />
            </key>
            <one-to-many class="netfile.model.filer.permissions.PermissionDataspace, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
          </bag>
        </join>
        <subclass name="netfile.model.filer.entities.UserSupport, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="UserSupport">
          <join table="Entity_UserSupport">
            <key>
              <column name="Entity_id" />
            </key>
            <property name="CompanyName">
              <column name="CompanyName" />
            </property>
          </join>
        </subclass>
      </subclass>
    </subclass>
    <!-- MunicipalDecision, MunicipalDecisionSfo -->
    <subclass name="netfile.model.filer.entities.lobbyist.MunicipalDecision, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="MunicipalDecision">
      <join table="Entity_MunicipalDecision">
        <key>
          <column name="Entity_id" />
        </key>
        <property name="Description">
          <column name="Description" />
        </property>
        <property name="OutcomeSought">
          <column name="OutcomeSought" />
        </property>
      </join>
    </subclass>
    <!-- MunicipalDecisionSfo -->
    <subclass name="netfile.model.filer.entities.lobbyist.sfo.MunicipalDecisionSfo, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" discriminator-value="MunicipalDecisionSfo">
      <join table="Entity_MunicipalDecision">
        <key>
          <column name="Entity_id" />
        </key>
        <property name="Description">
          <column name="Description" />
        </property>
        <property name="OutcomeSought">
          <column name="OutcomeSought" />
        </property>
        <property name="FileNumber">
          <column name="FileNumber" />
        </property>
        <many-to-one class="netfile.model.filer.settings.ownership.AgencyDefinedLobbyingSubjectArea, netfile.data.filer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="SubjectArea">
          <column name="SubjectArea_id" />
        </many-to-one>
      </join>
    </subclass>
  </class>
</hibernate-mapping>

Answer 1

你的错误是你的数据库设计得很糟糕。您正在使用每个子类一个表的映射策略，但您已将其应用于许多明显不相关的类。组织如何拥有名字或姓氏？

当你获得一个实体时，NHibernate 必须连接继承树中的所有表，因为它不知道要返回什么具体类型。如果您获得一个用户或组织，它只会按预期连接到另一个表。

Entity 是抽象类吗？您无法获取 Entity 类型的具体对象，因为无法构造抽象类。

编辑添加：看到映射文件后，我真的认为你应该重新考虑你的设计。这不是继承的良好或合理的使用。如果您确实想继续使用此模型，我建议保留抽象基类但不映射它。但我认为这个设计还有比这更深层次的问题。

Answer 2

Polymorphism="explicit" 应该放入我的类声明中。 NHibernate 中默认多态性是隐式的。

Answer 3

如果不进行连接，NHibernate 就不知道要返回一个 User 或 Entity 实例。您无法避免这种加入。当您保存用户时，您会恢复一个用户。如果您不想“找回用户”，您可以保存实体而不是用户。

Answer 4

您必须告诉您的配置文件您想要延迟加载

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哦。所以事实证明，当我回答时我并没有正确醒来:)

我搜索了一些关于这个主题的信息，并且可以向您指出mookid 的这篇文章（我猜他也是这里）这证实了 Jamie Ides 的身份也就是说，基本上你可能在这里有一种代码味道。也许重新考虑类及其映射可能是一个更好的主意。