i have a query that gets the user who have a specific book in their bookshelf but im not sure i understand why this takes place every time i load a user.... could someone explain why?

Hibernate: select user0_.user_id as user_id,.......
Hibernate: select booklines0_.user_id ....

Hibernate: delete from BOOK_LINES where user_id=? and isbn=? and date=? and available=?

Hibernate: insert into BOOK_LINES (user_id, isbn, date, available) values (?, ?, ?, ?)


the query
session.find("select u from User u inner join u.bookshelf.booklines bl inner join bl.book b where b.isbn='"+isbn+"'");

Hibernate version:latest

Mapping documents:
<hibernate-mapping package="dk.bytenbog.model.businessobject">
<class name="User" table="USER">

<id name="username" type="string" column="user_id">
<generator class="assigned"/>
</id>

<property name="password" type="string" column="password"/>
....
....

<component name="bookshelf" class="Bookshelf">

<set name="booklines" table="BOOK_LINES" cascade="all" lazy="true">
<key column="user_id"/>

<composite-element class="Bookline">
<many-to-one name="book" class="Book">
<column name="isbn"/>
</many-to-one>

<property name="date" type="date" column="date"/>
....

</composite-element>
</set>

</component>
</class>


Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using:

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

i guess it had something to do with not implementing equals and hashCode right