迁移 Hibernate 混合 inheritance 从 hbm.xml 到 orm.xml

Question

Consider the following Java hierarchy:

I want the whole hierarchy to be stored in a single table named file , except for SpecialOutFile which should have its dedicated special_file table.

This works perfectly well using hbm.xml mappings:

<?xml version="1.0" encoding="UTF-8"?>
<hibernate-mapping xmlns="http://www.hibernate.org/xsd/hibernate-mapping"
                   default-access="field"
                   default-cascade="all"
                   default-lazy="true">

    <class name="com.example.demo.File">
        <id name="id"/>
        <discriminator column="file_type"/>

        <subclass name="com.example.demo.InFile" discriminator-value="InFile"/>
        <subclass name="com.example.demo.TypedOutFile1" discriminator-value="TypedOutFile1"/>
        <subclass name="com.example.demo.TypedOutFile2" discriminator-value="TypedOutFile2"/>
        <subclass name="com.example.demo.OutFile" discriminator-value="OutFile"/>
    </class>

    <class name="com.example.demo.SpecialOutFile" table="special_file">
        <id name="id"/>
        <property name="moreData"/>
    </class>
</hibernate-mapping>

When I persist an OutFile , only one record is inserted, in file .
When I persist a SpecialOutFile , only one record is inserted, in special_file .

Now I'd like to do the same in orm.xml, as hbm.xml became deprecated in Hibernate 6. However, I cannot manage to reproduce the exact same behavior.

The closest I can get is using a secondary table, but now when I persist a SpecialOutFile two records are created: one in file and one in special_file :

Hibernate: insert into file (some_data, type, id) values (?, 'SpecialOutFile', ?)
Hibernate: insert into special_file (more_data, id) values (?, ?)

Here's my current version of orm.xml:

<?xml version="1.0" encoding="UTF-8"?>
<entity-mappings version="2.0"
                 xmlns="http://java.sun.com/xml/ns/persistence/orm"
                 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm http://java.sun.com/xml/ns/persistence/orm_2_0.xsd">

    <access>FIELD</access>

    <entity class="com.example.demo.File">
        <discriminator-column name="type"/>
        <attributes>
            <id name="id"/>
        </attributes>
    </entity>

    <entity class="com.example.demo.InFile">
        <discriminator-value>InFile</discriminator-value>
    </entity>
    <entity class="com.example.demo.TypedOutFile1">
        <discriminator-value>TypedOutFile1</discriminator-value>
    </entity>
    <entity class="com.example.demo.TypedOutFile2">
        <discriminator-value>TypedOutFile2</discriminator-value>
    </entity>
    <entity class="com.example.demo.OutFile">
        <discriminator-value>OutFile</discriminator-value>
    </entity>

    <entity class="com.example.demo.SpecialOutFile">
        <secondary-table name="special_file"/>
        <attribute-override name="id">
            <column table="special_file"/>
        </attribute-override>
        <attributes>
            <basic name="moreData">
                <column table="special_file"/>
            </basic>
        </attributes>
    </entity>
</entity-mappings>

Is there a way to move all inherited attributes into the secondary table and completely get rid of the primary table when persisting a SpecialOutFile , like I was able to do with hbm.xml mappings?

Minimal reproducible exemple here: https://github.com/bjansen/so-question-75328749

Answer 1

I think what you are looking for is discriminator based joined inheritance: https://en.wikibooks.org/wiki/Java_Persistence/Inheritance#Example_joined_inheritance_XML

You'd just mention the same table name for every class except for the SpecialOutFile one.