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POhibernate cascading delete, why not one delete on the foreign key?
 

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  1. POhibernate cascading delete, why not one delete on the foreign key?
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    <p>I'm wondering why hibernate generates 1 delete per entity on a child table instead of using one delete on the foreign key</p> <p>Here's the hibernate.cfg.xml (No i's not the next SO :-t</p> <pre><code>&lt;hibernate-configuration&gt; &lt;session-factory&gt; &lt;property name="hibernate.connection.url"&gt;jdbc:hsqldb:file:testdb;shutdown=true&lt;/property&gt; &lt;property name="hibernate.connection.driver_class"&gt;org.hsqldb.jdbcDriver&lt;/property&gt; &lt;property name="hibernate.connection.username"&gt;sa&lt;/property&gt; &lt;property name="hibernate.connection.password"&gt;&lt;/property&gt; &lt;property name="hibernate.connection.pool_size"&gt;0&lt;/property&gt; &lt;property name="hibernate.dialect"&gt;org.hibernate.dialect.HSQLDialect&lt;/property&gt; &lt;property name="hibernate.show_sql"&gt;true&lt;/property&gt; &lt;property name="hibernate.format_sql"&gt;true&lt;/property&gt; &lt;property name="hbm2ddl.auto"&gt;auto&lt;/property&gt; &lt;mapping file="entities/Question.hbm.xml"/&gt; &lt;mapping file="entities/Answer.hbm.xml"/&gt; &lt;/session-factory&gt; </code></pre> <p>Question.hbm.xml</p> <pre><code>&lt;hibernate-mapping&gt; &lt;class name="entities.Question"&gt; &lt;id name="id"&gt; &lt;generator class="native" /&gt; &lt;/id&gt; &lt;property name="title" not-null="true"&gt; &lt;/property&gt; &lt;property name="question" type="text" not-null="true"&gt; &lt;/property&gt; &lt;bag name="answers" inverse="true" cascade="all,delete-orphan" &gt; &lt;key&gt; &lt;column name="questionId" index="answer_questionId_idx" not-null="true"/&gt; &lt;/key&gt; &lt;one-to-many class="entities.Answer" /&gt; &lt;/bag&gt; &lt;property name="created" update="false" &gt; &lt;column name="created" not-null="true" index="answer_created_idx"&gt;&lt;/column&gt; &lt;/property&gt; &lt;property name="lastUpdated"&gt; &lt;column name="lastUpdated" not-null="true" index="answer_lastUpdated_idx"&gt;&lt;/column&gt; &lt;/property&gt; &lt;/class&gt; &lt;/hibernate-mapping&gt; </code></pre> <p>Answer.hbm.xml</p> <pre><code>&lt;hibernate-mapping&gt; &lt;class name="entities.Answer"&gt; &lt;id name="id"&gt; &lt;generator class="native" /&gt; &lt;/id&gt; &lt;property name="answer" type="text" not-null="true"&gt; &lt;/property&gt; &lt;property name="created" update="false" &gt; &lt;column not-null="true" name="created" index="question_created_idx"&gt;&lt;/column&gt; &lt;/property&gt; &lt;property name="lastUpdated" &gt; &lt;column name="lastUpdated" not-null="true" index="question_lastUpdated_idx"&gt;&lt;/column&gt; &lt;/property&gt; &lt;many-to-one name="question" column="questionId" not-null="true" update="false"&gt; &lt;/many-to-one&gt; &lt;/class&gt; &lt;/hibernate-mapping&gt; </code></pre> <p>There's 1 Question and 2 answers in my database, this test code:</p> <pre><code>Session session = factory.openSession(); Transaction t = session.beginTransaction(); Question q = (Question) session.load(Question.class,1); session.delete(q); t.commit(); session.close(); </code></pre> <p>I would expect it to generate SQL like,</p> <pre><code>select .... from Questions where id = 1; delete from Answers where questionId=1; delete from Question where id=1; </code></pre> <p>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:</p> <pre><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=? </code></pre> <p>How come, and is there anything I can do about it ?</p> <p>Edit, in response to Nate Zaugg, I can get the db to do the cascading delete by setting on-delete="cascade" on the one-to-many key mapping, i'm more wondering why hibernate does what it does and not does one delete on the Answers table, and wheter threre's something wrong with my mappings.</p>
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