CREATE TABLE `Users` (
  `userid` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(80) DEFAULT NULL,
  PRIMARY KEY (`userid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

CREATE TABLE `userpreferences` (
  `preferenceid` bigint(20) NOT NULL AUTO_INCREMENT,
  `userid` bigint(20) NOT NULL,
  `prefname` varchar(100) DEFAULT NULL,
  `prefvalue` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`preferenceid`),
  KEY `fk_pref_user_id` (`userid`),
  CONSTRAINT `fk_user_pref_id` FOREIGN KEY (`userid`) REFERENCES `userss` (`userid`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8$$

public class user implements Serializable, Comparable<user>{
private Long userId;
private String name;
private Set<UserPreference> preferences;
}

public class UserPreference{
public Long preferenceId;
private String prefName;
private String prefValue;
private User user;
}

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>               
   <class name="User" table="user">
      <id name="userid" type="java.lang.Long" column="userId">
         <generator class="native" />
      </id>
      <property name="name" type="string" length="80" />
   
      <set name="preferences" table="userpreferences" lazy="true" inverse="true" cascade="all-delete-orphan" fetch="select">
         <key column="userid" not-null="true"/>
         <one-to-many class="UserPreferences" />
      </set>
   </class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>               
   <class name="UserPreferences" table="userpreferences" >
      <id name="preferenceId" type="java.lang.Long">
         <column name="preferenceId" />
         <generator class="native" />
      </id>
      <many-to-one name="user" column="userId" class="User" fetch="select" not-null="true"/>
      <property name="prefName" type="string" >
         <column name="prefname" length="100" not-null="true"  />
      </property>
      <property name="prefValue" type="string" >
         <column name="prefvalue" length="100" not-null="true"  />
      </property>
   </class>
</hibernate-mapping>

user.setId(0L);
user.setName("test");
session.save(user);
            
Map<String, String> defaultPref =  Util.getDefaultPreferences();
UserPreferences prefs =  null;
for(String key : defaultPref.keySet()){
    prefs = new UserPreferences();
    prefs.setPreferenceId(0L);
    prefs.setPrefName(key);
    prefs.setPrefValue(defaultPref.get(key));
    prefs.setUser(user);
    session.save(prefs); //error line
}

DEBUG: org.springframework.orm.hibernate3.HibernateTransactionManager - Found thread-bound Session [org.hibernate.impl.SessionImpl@19e6d8ab] for Hibernate transaction
DEBUG: org.springframework.orm.hibernate3.HibernateTransactionManager - Participating in existing transaction
DEBUG: org.hibernate.event.def.AbstractSaveEventListener - executing identity-insert immediately
DEBUG: org.hibernate.jdbc.AbstractBatcher - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
DEBUG: org.hibernate.SQL - insert into users(userid, name) values (?, ?)
Hibernate: insert into users (userid, name) values (?, ?)
DEBUG: org.hibernate.id.IdentifierGeneratorFactory - Natively generated identity: 32
DEBUG: org.hibernate.jdbc.AbstractBatcher - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
DEBUG: org.hibernate.event.def.AbstractSaveEventListener - executing identity-insert immediately
DEBUG: org.hibernate.jdbc.AbstractBatcher - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
DEBUG: org.hibernate.SQL - insert into userpreferences (userid, prefkey, prefvalue) values (?, ?, ?)
Hibernate: insert into userpreferences (userid, prefkey, prefvalue) values (?, ?, ?)
DEBUG: org.hibernate.jdbc.AbstractBatcher - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
DEBUG: org.hibernate.util.JDBCExceptionReporter - could not insert: [UserPreferences] [insert into userpreferences (userid, prefkey, prefvalue) values (?, ?, ?)]
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'prefkey, prefvalue) values (32, 'aggregate', '1')' at line 1
   at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
   at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
   at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
   at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
   at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)