带鉴别器的Hibernate映射

http://docs.jboss.org/hibernate/core/3.5/reference/en-US/html/mapping.html#mapping-declaration-discriminator

元素是 多态持久性所必需的 表的鉴别器列。这个 鉴别器列包含标记 要为一个类实例化哪个子类 特定行。

我不认为您能够为这些不同的含义使用单个AdminNote类。鉴别器在数据库级别用于帮助区分一个子类和另一个子类——它实际上不是java对象模型的一部分。

作为整数的鉴别器

无法使用(…)将鉴别器值“TYPE”格式化为SQL字符串

如果希望将鉴别器用作整数值,首先需要通过在class元素中设置鉴别器值属性,将基类的鉴别器值指定为整数:

<class name="AdminNotes" table="admin_notes" abstract="true" discriminator-value= "-1">

这将替换默认行为,即当找不到值时,鉴别器是类名。

<hibernate-mapping package="com.tlr.finance.mappings">

    <class name="AdminNotes" table="admin_notes" abstract="true" discriminator-value= "-1">
        <id name="adminNoteId" column="admin_note_id" type="integer">
            <generator class="identity" />
        </id>
        <discriminator column="note_type" type="integer" />

        <!-- Make this property an enumerated type. It is the discriminator. -->
        <property name="adminNoteType" column="note_type" type="string" not-null="true" />
        <property name="adminNote" column="note" type="string" not-null="true" />
        <property name="adminNoteAdded" column="note_date" type="timestamp"
                  not-null="true" />

        <subclass name="AdminNotes" discriminator-value="0" entity-name="project">
            <many-to-one name="noteObject" column="object_id" class="PsData" /><!-- Project -->
        </subclass>

        <subclass name="AdminNotes" discriminator-value="1" entity-name="user">
            <!-- Rename timekeep to user -->
            <many-to-one name="noteObject" column="object_id" class="Timekeep" /><!-- user -->
        </subclass>

        <subclass name="AdminNotes" discriminator-value="2" entity-name="costCenter">
            <!-- Rename timekeep to user -->
            <many-to-one name="noteObject" column="object_id" class="CostCenter" /><!-- cost center -->
        </subclass>
    </class>
</hibernate-mapping>

另外,如果您使用实体名称,您可以为子类映射重用Java类名。

API ,或在Tuplizer中实现实体名称解析( Hibernate 3.3.2)基于adminNoteType字段。

<hibernate-mapping package="com.tlr.finance.mappings">

    <class name="AdminNotes" table="admin_notes" abstract="true">
        <id name="adminNoteId" column="admin_note_id" type="integer">
          <generator class="identity" />
        </id>

        <discriminator column="note_type" type="string" />

        <!-- Make this property an enumerated type. It is the discriminator. -->
        <property name="adminNoteType" column="note_type" type="string" not-null="true" />
        <property name="adminNote" column="note" type="string" not-null="true" />
        <property name="adminNoteAdded" column="note_date" type="timestamp"
          not-null="true" />

        <subclass name="AdminNotes" discriminator-value="project" entity-name="project">
            <many-to-one name="noteObject" column="object_id" class="PsData" /><!-- Project -->
        </subclass>

        <subclass name="AdminNotes" discriminator-value="user" entity-name="user">
            <!-- rename timekeep to user -->
            <many-to-one name="noteObject" column="object_id" class="Timekeep" /><!-- user -->
        </subclass>

        <subclass name="AdminNotes" discriminator-value="costCenter" entity-name="costCenter">
            <!-- rename timekeep to user -->
            <many-to-one name="noteObject" column="object_id" class="CostCenter" /><!-- cost center -->
        </subclass>
    </class>
</hibernate-mapping>

代替尝试使用继承能力来获取对正确类的引用,而是应该考虑使用 <any/> 使用 note_type 要确定 object_id noteObject

有关 < ,见 Any type mappings "在 NHibernate 文档和博客文章 NHibernate Mapping