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Repeated column in mapping for entity, oneToMany relationship

I am trying to do a one-to-many relationship between two tables. I have a table called users that has many user_history entries. I defined these tables in mysql and I generated the entities with intellij hibrernate support. The problem is that when i want to insert something in the databse I am receiving the following error Repeated column in mapping for entity: com.UserHistoryEntity
User:
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.UsersEntity" table="users" schema="" catalog="protein_tracker">
<id name="id">
<column name="id" sql-type="int" not-null="true"/>
</id>
<property name="name">
<column name="name" sql-type="varchar" length="45" not-null="true"/>
</property>
<property name="total">
<column name="total" sql-type="int" not-null="true"/>
</property>
<property name="goal">
<column name="goal" sql-type="int" not-null="true"/>
</property>
<set name="userHistoriesById" inverse="true">
<key>
<column name="id_user" not-null="true"/>
</key>
<one-to-many not-found="ignore" class="com.UserHistoryEntity"/>
</set>
</class>
</hibernate-mapping>
UserHistory:
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.UserHistoryEntity" table="user_history" schema="" catalog="protein_tracker">
<id name="id">
<column name="id" sql-type="int" not-null="true"/>
</id>
<property name="entryDate">
<column name="entry_date" sql-type="datetime" not-null="true"/>
</property>
<property name="entry">
<column name="entry" sql-type="varchar" length="45" not-null="true"/>
</property>
<property name="idUser">
<column name="id_user" sql-type="int" not-null="true"/>
</property>
<many-to-one name="usersByIdUser" class="com.UsersEntity">
<column name="id_user" not-null="true"/>
</many-to-one>
</class>
</hibernate-mapping>
How can I fix this issue?

Mark your Many-To-One mapping for usersByIdUser to insertable = false and updatable = false. This allows the relationship to only be managed by a single property, idUser that you have mapped.

How do I cascade saves through a many to many relationship with hibernate?

I have a many to many (with a join table) relationship in my database that I need to model in hibernate.
I have POJO classes for all three tables in the database as the join table contains more than just the mapping information.
My problem occurs on save() of class A where class A is told to cascade to class AB (the join table) which is told to cascade to class B, but when it gets to the point where it is saving AB the foriegn key reference to table A is null.
At the end of the day I want to be able to call save() on an instance of the TableA class and have it save all three tables.
Table Diagram
TABLE A 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">
<!-- Generated Aug 27, 2012 2:16:37 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
<class name="com.example.dbtables.TableA" table="Table A">
<id name="id" type="int">
<column name="id" />
<generator class="sequence">
<param name="sequence">table_a_seq</param>
</generator>
</id>
<natural-id>
<property name="data1" type="int">
<column name="DATA1" not-null="true" />
</property>
<property name="data2" type="string">
<column name="DATA2" length="16" not-null="true" />
</property>
</natural-id>
<set name="tableAB" cascade="save-update" table="TableAB" inverse="true" lazy="true" fetch="select">
<key>
<column name="Table_AB_ID" not-null="true" />
</key>
<one-to-many class="com.example.dbtables.TableAB" />
</set>
</class>
</hibernate-mapping>
TABLE AB 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">
<!-- Generated Aug 27, 2012 2:16:37 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
<class name="com.example.dbtables.TableAB" table="Table AB">
<id name="id" type="int">
<column name="id" />
<generator class="sequence">
<param name="sequence">table_ab_seq</param>
</generator>
</id>
<natural-id>
<many-to-one name="tableA" class="com.example.dbtables.TableA" fetch="select">
<column name="Table_A_ID" not-null="true" />
</many-to-one>
<many-to-one name="tableB" cascade="save-update" class="com.example.dbtables.TableB" fetch="select">
<column name="Table_B_ID" not-null="true" />
</many-to-one>
<property name="data1" type="int">
<column name="DATA1" not-null="true" />
</property>
<property name="data2" type="int">
<column name="DATA2" not-null="true" />
</property>
</natural-id>
</class>
</hibernate-mapping>
TABLE B 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">
<!-- Generated Aug 27, 2012 2:16:37 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
<class name="com.examples.dbtables.TableB" table="Table B">
<id name="id" type="int">
<column name="id" />
<generator class="sequence">
<param name="sequence">table_b_seq</param>
</generator>
</id>
<natural-id>
<property name="data1" type="string">
<column name="DATA1" length="16" />
</property>
<property name="data2" type="java.lang.Integer">
<column name="DATA2" />
</property>
</natural-id>
<set name="TableAB" table="Table AB" inverse="true" lazy="true" fetch="select">
<key>
<column name="Table_AB_ID" not-null="true" />
</key>
<one-to-many class="com.example.dbtables.TableAB" />
</set>
</class>
</hibernate-mapping>
Thanks for any help you can give. Let me know if you need clarification or anymore information.
EDIT: My problem was that the references from AB -> to A were not getting correctly populated. This issue has been resolved thanks to everyone who helped.

A a = new A();
B b = new B();
AB ab = new AB();
ab.setA(a);
ab.setB(b);
a.setAB(ab);
b.setAB(ab);
save(a);
This example not working? Did you get some exception?
EDIT
Look into this Hibernate doc Chapter 5. Basic O/R Mapping to chapter 5.1.4.1. Generator
PostgreSQL doesn't support identity generation type.
Use sequence generation instead of identity, or something else

The problem was that the back references between AB -> A were not getting correctly populated in my code. Thanks to Ilya for the help.

Hibernate One-To-Many Could Not Initialise Collection

I have two database tables, User and PageComment. Using Hibernate, I'm trying to store a Set of PageComment objects in the User comment (comments made to that user), by using one-to-many relationship in the hbm XML files.
The problem is, I seem to be able to retrieve the set from a User object, but as soon as I try to access any of the objects stored within the set, or even access on of the methods included in the set class (i.e. size()), the JVM throws "org.hibernate.exception.GenericJDBCException: could not initialize a collection". I'm at a loss on this one.
HBM For User Table:
<?xml version="1.0" encoding="UTF-8"?>
<!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="username" column="Username" type="string">
<generator class="assigned"></generator>
</id>
<property name="password" column="Password" type="string"></property>
<property name="firstname" column="Firstname" type="string"></property>
<property name="surname" column="Surname" type="string"></property>
<property name="email" column="Email" type="string"></property>
<property name="admin" column="Admin" type="integer"></property>
<set name="commentsMadeTo" inverse="true">
<key column="userMadeTo"/>
<one-to-many class="PageComment"/>
</set>
</class>
</hibernate-mapping>
HBM For PageComment:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="PageComment" table="PageComment">
<composite-id>
<key-property name="userMadeBy" column="UserMadeBy" type="string" />
<key-property name="userMadeTo" column="UserMadeTo" type="string" />
<key-property name="time" column="Time" type="integer" />
<generator class="assigned"></generator>
</composite-id>
<property name="commentText" column="CommentText" type="string"></property>
<many-to-one name="userMadeTo" column="Username" not-null="true" class="User" />
</class>
</hibernate-mapping>
I'm trying to test the mapping with this method:
Session session = sessionFactory.openSession();
User theUser = (User)session.createQuery("FROM User WHERE Username='Samat'").uniqueResult();
System.out.println("Trying to print out all comments made to 'Samat'");
Set<PageComment> theComments = theUser.getCommentsMadeTo();
for(PageComment p: theComments){
System.out.println(p.getAllData());
}

I spot that there are some problems in the relationship mapping
HBM For User Table:
<set name="commentsMadeTo" inverse="true">
<key column="XXXXXXXX"/>
<one-to-many class="PageComment"/>
</set>
HBM For PageComment:
<many-to-one name="userMadeTo" column="XXXXXXX" not-null="true" class="User" />
The value XXXXX represents the column name on the "many" side (i.e PageComment table in your case) that associates to its "One" side. It should have the same value in both mapping hbm.
Try to change the hbm for user table to:
<set name="commentsMadeTo" inverse="true">
<key column="Username"/>
<one-to-many class="PageComment"/>
</set>

Unable to use inheritence in Hibernate

Please have a look at the following
<?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="com.att_marks.students.Attendance_Btech">
<id name="id" type="integer" column="id" >
<generator class="increment"/>
</id>
<property name="year">
<column name="Year" />
</property>
<property name="semister">
<column name="Semister"/>
</property>
<property name="section">
<column name="Section"/>
</property>
<property name="period">
<column name="Period"/>
</property>
<property name="subjectCode">
<column name="Subject_Code"/>
</property>
<property name="date">
<column name="Date"/>
</property>
<property name="status">
<column name="Status"/>
</property>
<union-subclass name="com.att_marks.students.Attendance_Btech_ECE" table="attendance_btech_ece">
</union-subclass>
</class>
</hibernate-mapping>
I have tables named attendance_btech_ece, attendance_btech_cse, attendance_btech_it, and so on. All these tables use the same schema as mentioned above for the Attendance_Btech class. I thought this should work but it isn't.

If the Attendance_Btech_ECE is subclass of Attendance_Btech then should work.

Hibernate Loading not loading the whole tree

I am trying to make hibernate load my whole tree with no success.
I have a schema like this
A Category can have many attribute and an attribute can have many options
Category
--->Attribute1
--->AttributeOption1
--->AttributeOption3
--->Attribute2
--->AttributeOption1
--->AttributeOption1
but when I am using hibernate, it is not loading the whole tree:
my mapping file are:
Attribute Mapping FIle:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Dec 16, 2010 5:25:09 AM by Hibernate Tools 3.4.0.Beta1 -->
<hibernate-mapping>
<class name="com.BiddingSystem.Models.Attribute" table="ATTRIBUTE">
<id name="AttributeId" type="long">
<column name="ATTRIBUTEID" />
<generator class="native" />
</id>
<property name="AttributeName" type="java.lang.String">
<column name="ATTRIBUTENAME" />
</property>
<set name="Options" table="ATTRIBUTEOPTION" inverse="false" cascade="all" lazy="true">
<key>
<column name="ATTRIBUTEID" />
</key>
<one-to-many class="com.BiddingSystem.Models.AttributeOption" />
</set>
</class>
</hibernate-mapping>
Attribute Option Mapping File:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Dec 16, 2010 5:25:09 AM by Hibernate Tools 3.4.0.Beta1 -->
<hibernate-mapping>
<class name="com.BiddingSystem.Models.AttributeOption" table="ATTRIBUTEOPTION">
<id name="AttributeOptionId" type="long">
<column name="ATTRIBUTEOPTIONID" />
<generator class="native" />
</id>
<property name="Option" type="java.lang.String">
<column name="OPTION" />
</property>
<property name="SQLValue" type="java.lang.String">
<column name="SQLVALUE" />
</property>
</class>
</hibernate-mapping>
Category Mapping File:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Dec 16, 2010 8:37:02 AM by Hibernate Tools 3.4.0.Beta1 -->
<hibernate-mapping>
<class name="com.BiddingSystem.Models.Category" table="CATEGORY">
<id name="CategoryId" type="long">
<column name="CATEGORYID" />
<generator class="native" />
</id>
<property name="CategoryName" type="java.lang.String">
<column name="CATEGORYNAME" />
</property>
<many-to-one name="ParentCategory" class="com.BiddingSystem.Models.Category">
<column name="PARENT_CATEGORY_ID" />
</many-to-one>
<set name="SubCategory" lazy="true" cascade="all-delete-orphan" inverse="true">
<key>
<column name="PARENT_CATEGORY_ID" />
</key>
<one-to-many class="com.BiddingSystem.Models.Category" />
</set>
<set name="AllAttributes" table="ATTRIBUTE" inverse="false" lazy="true" cascade="all">
<key>
<column name="CATEGORYID" />
</key>
<one-to-many class="com.BiddingSystem.Models.Attribute" />
</set>
</class>
</hibernate-mapping>
The function that loads the parent category are:
public List <Category> getCategory(long CategoryId)
{
Session session = gileadHibernateUtil.getSessionFactory().openSession();
List <Category> AllCategory= new LinkedList<Category> ();
String SQL="from Category where parent_category_id is NULL";
Query query = session.createQuery(SQL);
return query.list();
}

Make all your associations lazy=false; by default the lazy = true

I believe there is an other mistake:
String SQL="from Category where parent_category_id is NULL";
Query query = session.createQuery(SQL);
org.hibernate.Session.createQuery(String queryString) requires a HQL Query String, but not a SQL query! And from Category where parent_category_id is NULL seems to be a SQL query, because parent_category_id is a column name but not a property / field name.