ERROR: Failed to lazily initialize a collection - no Session
net.sf.hibernate.LazyInitializationException: Failed to lazily initialize a collection - no Session
   at net.sf.hibernate.collection.PersistentCollection.initialize(PersistentCollection.java:213)
   at net.sf.hibernate.collection.PersistentCollection.read(PersistentCollection.java:69)
   at net.sf.hibernate.collection.Set.toString(Set.java:219)
( ... )

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
   
<hibernate-mapping>
<!--
    Created by Middlegen Hibernate plugin

    http://boss.bekk.no/boss/middlegen/
    http://hibernate.sourceforge.net/
-->

<class
    name="vo.Mistura"
    table="mistura"
>

    <id
        name="id"
        type="long"
        column="id"
    >
        <generator class="increment" />
    </id>
   
    <property
        name="userId"
        type="java.lang.String"
        column="user_id"
        not-null="true"
        length="10"
    />

    <!-- associations -->
    <!-- bi-directional one-to-many association to MisturaStock -->
    <set
        name="misturaStocks"
        lazy="true"
        inverse="true"
    >
        <key>
            <column name="mistura_fk" />
        </key>
        <one-to-many
            class="vo.MisturaStock"
        />
    </set>

</class>
</hibernate-mapping>

SessionFactory sessionFactory = HibernateFactory.createFactory();
session = sessionFactory.openSession();

res = session.find("from vo.Mistura as m " +
         "left join fetch misturaStocks " +
         "where m.userId= '" + user + "'");

   
session.close();