I'm wondering why hibernate generates 1 delete per entity on a child table
instead of using one delete on the foreign key
Here's the hibernate.cfg.xml for this toy project
Code:
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.url">jdbc:hsqldb:file:testdb;shutdown=true</property>
<property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property>
<property name="hibernate.connection.username">sa</property>
<property name="hibernate.connection.password"></property>
<property name="hibernate.connection.pool_size">0</property>
<property name="hibernate.dialect">org.hibernate.dialect.HSQLDialect</property>
<property name="hibernate.show_sql">true</property>
<property name="hibernate.format_sql">true</property>
<property name="hbm2ddl.auto">auto</property>
<mapping file="entities/Question.hbm.xml"/>
<mapping file="entities/Answer.hbm.xml"/>
</session-factory>
Question.hbm.xml
Code:
<hibernate-mapping>
<class name="entities.Question">
<id name="id">
<generator class="native" />
</id>
<property name="title" not-null="true">
</property>
<property name="question" type="text" not-null="true">
</property>
<bag name="answers" inverse="true" cascade="all,delete-orphan" >
<key>
<column name="questionId" index="answer_questionId_idx" not-null="true"/>
</key>
<one-to-many class="entities.Answer" />
</bag>
<property name="created" update="false" >
<column name="created" not-null="true" index="answer_created_idx"></column>
</property>
<property name="lastUpdated">
<column name="lastUpdated" not-null="true" index="answer_lastUpdated_idx"></column>
</property>
</class>
</hibernate-mapping>
Answer.hbm.xml
Code:
<hibernate-mapping>
<class name="entities.Answer">
<id name="id">
<generator class="native" />
</id>
<property name="answer" type="text" not-null="true">
</property>
<property name="created" update="false" >
<column not-null="true" name="created" index="question_created_idx"></column>
</property>
<property name="lastUpdated" >
<column name="lastUpdated" not-null="true" index="question_lastUpdated_idx"></column>
</property>
<many-to-one name="question" column="questionId" not-null="true" update="false">
</many-to-one>
</class>
</hibernate-mapping>
There's 1 Question and 2 answers in my database, this test code:
Code:
Session session = factory.openSession();
Transaction t = session.beginTransaction();
Question q = (Question) session.load(Question.class,1);
session.delete(q);
t.commit();
session.close();
I would expect it to generate SQL like,
Quote:
select .... from Questions where id = 1;
delete from Answers where questionId=1;
delete from Question where id=1;
I.e., just issue one delete to do the cascading delete on Answers,
instead it's loading all the answers and issuing one delete per answer, like:
Code:
select
question0_.id as id0_0_,
question0_.title as title0_0_,
question0_.question as question0_0_,
question0_.created as created0_0_,
question0_.lastUpdated as lastUpda5_0_0_
from
Question question0_
where
question0_.id=?
select
answers0_.questionId as questionId0_1_,
answers0_.id as id1_,
answers0_.id as id1_0_,
answers0_.answer as answer1_0_,
answers0_.created as created1_0_,
answers0_.lastUpdated as lastUpda4_1_0_,
answers0_.questionId as questionId1_0_
from
Answer answers0_
where
answers0_.questionId=?
delete from Answer where id=?
delete from Answer where id=?
delete from Question where id=?
How come, and is there anything I can do about it ?
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