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Hibernate Mapping issue when lazily loading a Set of custom Objects

I have trying to read from my database using Hibernate but I am having a problem. Any help would be appreciated. It has to do with the fact that there is a set of Answers in a Question object and I'm not sure the implications this is having on the subject.
List<Question> questions = session
.createQuery("from Question where topic = :id")
.setParameter("id", topic)
.list();
Code:
<class name="cdd.model.Question" table="question">
<id column="question_id" name="questionID" type="org.hibernate.type.PostgresUUIDType">
<generator class="org.hibernate.id.UUIDGenerator"/>
</id>
<many-to-one class="cdd.model.User" column="submitted_by" name="submittedBy" not-null="true" lazy = "false"/>
<many-to-one class="cdd.model.Topic" column="question_topic" name="topic" not-null="true" lazy = "false"/>
<property column="title" name="title" type="org.hibernate.type.TextType"/>
<property column="correct_answer" name="correctAnswer" type="org.hibernate.type.TextType"/>
<property column="date_submitted" name="dateSubmitted" type="org.hibernate.type.TimestampType"/>
<property column = "approved" name = "approved" type = "org.hibernate.type.BooleanType"/>
<set cascade="all" name="answers" >
<key column="question_id" not-null="true" lazy = "false" />
<one-to-many class="cdd.model.Answer"/>
</set>
</class>
Java Class That was mapped:
public class Question {
UUID questionID;
User submittedBy;
Topic topic;
String title;
String correctAnswer;
Timestamp dateSubmitted;
boolean approved;
Set<Answer> answers;
/*Constructor, Getters and Setters*/
}
Error:
XML validation started.
Checking file:/Users/rhamblin/Desktop/CDDExamGen/src/hibernateMapping.hbm.xml...
Attribute "lazy" must be declared for element type "key". [69]
XML validation finished.

Hibernate Error indexing: null when checking if row exists

I am trying to check if a row exists in my database.
Word word = (Word) session.createQuery("select 1 from Word w where w.content = :key").setParameter("key",words[i]).uniqueResult();
I'm also trying:
Word word = session.get(Word.class,contentId);
Besides that I tried session.load,and some others. Everytime Hibernate returns error:
Error indexing: null
or
Error indexing: no row with the given identifier exists.
It is true, row does not existing but why doesn't it just returns null like it should for session.get:
http://docs.jboss.org/hibernate/orm/3.5/javadocs/org/hibernate/Session.html#get(java.lang.Class,%20java.io.Serializable).
In case of not finding a row I wanted to create one and add to a database but I'm not able to check if it exists.
EDIT:
Word.java
public class Word {
private String content;
private Set<Sentence> sentences;
empty constructor, setters and getters
}
Word.hbm.xml
<class name="Word">
<id name="content" column="wordId" type="string">
</id>
<set name="sentences" inverse="true">
<key><column name="wordId"/></key>
<many-to-many class="Sentence" column="sentenceId"/>
</set>
</class>
Sentence.java
public class Sentence {
private long id;
private ProcessedUrl processedUrl;
private List<Word> words;
empty constructor, setters and getters
}
Sentence.hbm.xml
<class name="Sentence">
<id name="id" column="sentenceId">
<generator class="native"/>
</id>
<many-to-one name="processedUrl" column="processedUrlId" not-null="true"/>
<list name="words">
<key>
<column name="sentenceId" not-null="true"/>
</key>
<list-index column="idx" />
<many-to-many class="Word">
<column name="wordId" not-null="true"/>
</many-to-many>
</list>
</class>

Hibernate: Where to map an additional column in a relating table?

I have two tables in a one-to-many relationship mapped by Hibernate:
<hibernate-mapping>
<class name="Class1" table="TABLE_1" dynamic-update="true">
<meta attribute="implement-equals">true</meta>
<cache usage="read-write"/>
<id name="id" column="KEY_1" length="5" >
....
</id>
<property name="property1a" column="COLUMN_1A" type="string" length="10" />
<property name="property1b" column="COLUMN_1B" type="string" length="10" />
<set name="properties2Set" table="TABLE_2" lazy="true" fetch="subselect" cascade="all">
<key column="FOREIGN_KEY_1"/>
<composite-element class="Class2">
<property name="property2a" type="string" column="COLUMN_2A"/>
<property name="property2b" type="string" column="COLUMN_2B"/>
<property name="property2c" type="string" column="COLUMN_2C"/>
</composite-element>
</set>
</class>
</hibernate-mapping>
Class1 looks like:
public class Class1
{
//... Here the definitions of property1a, property1b
private Set<Class2> properties2Set = new HashSet<Class2>();
public Set<Class2> getProperties2Set()
{
return properties2Set;
}
public void setProperties2Set(Set<Class2> properties2Set)
{
this.properties2Set = properties2Set;
}
// ... Definitions of equals() and hashCode()
}
Class2 contains properties property2a, property2b, property2c. There is a constraint
CONSTRAINT PK_OLD PRIMARY KEY (FOREIGN_KEY_1, COLUMN_2A, COLUMN_2B, COLUMN_2C)
I want to add to the table the column
COLUMN_ID_NUMBER NUMBER(5) DEFAULT 0 NOT NULL
change the constraint into
CONSTRAINT PK_NEW PRIMARY KEY (FOREIGN_KEY_1, COLUMN_ID_NUMBER)
and generate values of COLUMN_ID_NUMBER in order not to violate the constraint.
Where to add the property that would be mapped into COLUMN_ID_NUMBER and how to generate its values? Is it possible to leave the structure of Class2 unchanged?

LazyInitializationException with map collection

I know that it is a trite question, but I could not find a solution. I have two beans and one of them has HashMap collection. I'm getting an exception when trying to read this collection. Mapping config had been specified to load this collection eagerly.
My environment is :
Hibernate 4.2.0
mysql-connector-java 5.1.24
Also I have two beans:
public class FeaturedDoc {
private Long id;
private Map<Feature, Float> features;
public FeaturedDoc() {
features = new HashMap<Feature, Float>();
}
(getters and setters)
}
and
public class Feature {
private Long id;
private String name;
private Long internalId;
(getters and setters)
}
This beans have mapping:
<class name="Feature" table="FEATURE">
<id name="id" type="long" column="ID">
<generator class="increment"/>
</id>
<property name="name" length="255" type="string" unique="true" column="NAME" index="INDEX_NAME"/>
<property name="internalId" type="long" unique="true" not-null="false" column="INTERNAL_ID" index="INDEX_INTID"/>
<sql-insert>insert into FEATURE (NAME, INTERNAL_ID, ID) values (?, ?, ?) on duplicate key update ID = ID</sql-insert>
</class>
<class name="FeaturedDoc" table="FEATURED_DOC">
<id name="id" type="long" column="ID">
<generator class="increment"/>
</id>
<map name="features" table="DOC_FEATURE" cascade="all" lazy="false" fetch="join">
<key column="ID"></key>
<map-key-many-to-many column="FEATURE_ID" class="Feature"/>
<element column="value" type="float"/>
</map>
</class>
Also I have DAO layer with method:
public FeaturedDoc read(long id) {
FeaturedDoc fd = null;
try {
session.beginTransaction();
fd = session.get(FeaturedDoc.class, id);
session.getTransaction().commit();
} catch (Exception e) {
e.printStackTrace();
session.getTransaction().rollback();
} finally {
close();
}
return fd;
}
When I'm trying to do something like this:
FeaturedDoc fd = daoService.read(26);
System.out.println(fd.getFeatures());
I'm getting an exception
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
Do you know how should I fix this error?

Assuming that everything else is okay (in the mappings), have you tried putting lazy="false" before cascade="all". I found that this was a problem in my mapping which resulted in this LazyInitializationException error.
This ordering is shown in the following Hibernate Reference: http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/collections.html

I have solved this problem! The reason was in Feature class. It had not hashCode and equals functions. After implementation of these functions everything has become ok.

Hibernate One-to-many HashMap not updating on child

I have the following parent object which maps to a table in my database:
public Parent {
private Long id;
private String mid;
private Integer days;
private BigDecimal fee;
private DateTime createdDate = new DateTime();
private DateTime lastModifiedDate;
private Map<String, Child> children;
}
With the following .hbm.xml:
<hibernate-mapping default-access="field">
<class name="Parent" table="parent_table">
<id column="id" length="50" name="id" unsaved-value="null">
<generator class="increment"/>
</id>
<property length="50" name="mid"/>
<property name="days"/>
<property name="fee"/>
<property name="createdDate" type="(...)PersistentDateTime"/>
<property name="lastModifiedDate" type="(...)PersistentDateTime"/>
<map cascade="all-delete-orphan" inverse="true" name="children" >
<key column="parentId" />
<map-key column="country" type="string" />
<one-to-many class="Child" />
</map>
</class>
</hibernate-mapping>
The child object is as follows:
public class Child implements Serializable {
private Long parentId;
private String country;
private String cu;
}
With the following .hbm.xml:
<hibernate-mapping default-access="field">
<class name="Child" table="child_table">
<composite-id>
<key-property name="parentId"/>
<key-property name="country"/>
<key-property name="cu"/>
</composite-id>
</class>
</hibernate-mapping>
After acquiring a Parent object from my db via:
getSession().createCriteria(Parent.class)
.add(Restrictions.eq("mid", mid))
.uniqueResult();
After making some changes to Child.cu in the children map I call a saveOrUpdate on the Parent object. After doing so all appears to save / update fine but upon checking the child_table in the db, these changes have not been saved / updated.
I believe this has something to do with the mappings of the map in the Parent class but can't seem to figure it out. Any help would be appreciated.
Thanks in advance.

If I understand correctly, you're modifying a field which is part of the primary key of your entity. This is illegal: the ID should be immutable.
My advice is to follow the good practices: use a non-composite, purely technical, auto-generated primary key. Everything will be much simpler (and also faster).