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One-to-one - bidirectional - not lazy - N+1 select problem

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VincentLH

Post subject: One-to-one - bidirectional - not lazy - N+1 select problem

Posted: Mon Sep 05, 2011 12:15 pm

Newbie

Joined: Mon Sep 05, 2011 11:27 am
Posts: 4

Hello,

I am not able to define a mapping that retreive A or B (linked with a single not lazy bidirectional One-to-One association) with a single select.
I worked with @LazyToOne, EAGER, optional, fetch="join", "hibernate.max_fetch_depth", FetchProfile ... but I did not find how to achieve a single select.
I know that we can define this association with an other mapping like @PrimaryKeyJoinColumn and that a One-to-One mapping can be a bad design.

Why do I have several queries when I retreive an element with a one-to-one association defined with the following mapping ?
I am not looking for another mapping, I only want to understand why I have several queries.
If it is possible, how can I modify the mapping to solve the N+1 select problem.

In the following test case, I expected to send only one query to retreive A or B but I have respectively 3 and 2 select queries.

Best regards,

Vincent

Here is a simple test case :
Hibernate 3.6.5

hibernate.cfg.xml

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
 <session-factory>
   <!-- Config -->
   <!-- http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html_single/#session-configuration -->
    <property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.pool_size">10</property>
    
    <property name="hibernate.show_sql">true</property>
   <property name="hibernate.format_sql">false</property>
   
    <property name="hibernate.max_fetch_depth">1</property>
    <property name="hibernate.connection.autocommit">false</property>
    <property name="hibernate.cache.use_second_level_cache">false</property>
    <property name="hibernate.query.substitutions">yes 'Y', no 'N'</property>
    
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/testhibernate</property>
   <property name="hibernate.connection.username">username</property>
   <property name="hibernate.connection.password">password</property>
    
   <!-- mapping files -->
   <mapping class="fr.mycompany.hibernate.test.bo.A"/>
    <mapping class="fr.mycompany.hibernate.test.bo.B"/>
  </session-factory>
</hibernate-configuration>

Super class of A and B

Code:

package fr.mycompany.hibernate.test.bo;

import java.io.Serializable;
import java.util.Calendar;

import javax.persistence.Column;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import javax.persistence.Version;

@MappedSuperclass
public abstract class BusinessObject implements Serializable {

   private static final long serialVersionUID = 4179574695380922867L;

   /**
    * Technical primary key
    */
   protected Long id = null;

   protected Calendar timeStamp = null;

   public BusinessObject() {
   }

   @Id
   @Column(name = "ID", nullable = false)
   @GeneratedValue(strategy = GenerationType.AUTO)
   public Long getId() {
      return id;
   }

   public void setId(Long id) {
      this.id = id;
   }

   public void setId(long id) {
      this.id = new Long(id);
   }

   @Version
   @Column(name = "OBJ_OPT_LOCK", nullable = false)
   public Calendar getTimeStamp() {
      return timeStamp;
   }

   public void setTimeStamp(Calendar ts) {
      timeStamp = ts;
   }

   public abstract String asString();
}

A.java

Code:

package fr.mycompany.hibernate.test.bo;

import javax.persistence.Entity;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import javax.persistence.Transient;

import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.CascadeType;

@Entity
@Table(name = "A")
public class A extends BusinessObject {

   private static final long serialVersionUID = 87345767169183337L;

   public final static String BEAN_B = "b";

   private B b;

   public A() {
      super();
   }

   @OneToOne()
   @Cascade(value = { CascadeType.ALL })
   public B getB() {
      return b;
   }

   public void setB(B b) {
      this.b = b;
   }

   public void setRelationB(B value) {
      B newValue = value;
      B oldValue = getB();
      if (oldValue != null)
         oldValue.setA(null);
      if (newValue != null) {
         newValue.setRelationA(null);
         newValue.setA(this);
      }
      setB(value);
   }

   public void addB(B b) {
      setRelationB(b);
   }

   public void removeB(B b) {
      if (getB().equals(b))
         setB(null);
   }

   /**
    * Safely gets B from a B.
    * @return B
    */
   @Transient
   public B getRelationB() {
      return getB();
   }

   @Override
   public String asString() {
      return super.toString() + " -> " + getB().getId();
   }

}

B.java

Code:

package fr.mycompany.hibernate.test.bo;

import javax.persistence.Entity;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import javax.persistence.Transient;

import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.CascadeType;

@Entity
@Table(name = "B")
public class B extends BusinessObject {

   private static final long serialVersionUID = -5733931756299476473L;

   public final static String BEAN_A = "a";

   private A a;

   public B() {
      super();
   }

   @OneToOne(mappedBy = "b")
   @Cascade(value = { CascadeType.ALL })
   public A getA() {
      return a;
   }

   public void setA(A a) {
      this.a = a;
   }

   public void setRelationA(A value) {
      A newValue = value;
      A oldValue = getA();
      if (oldValue != null)
         oldValue.setB(null);
      if (newValue != null) {
         newValue.setRelationB(null);
         newValue.setB(this);
      }
      setA(value);
   }

   public void addA(A a) {
      setRelationA(a);
   }

   public void removeA(A a) {
      if (getA().equals(a))
         setA(null);
   }

   /**
    * Safely gets A from a A.
    * @return A
    */
   @Transient
   public A getRelationA() {
      return getA();
   }

   @Override
   public String asString() {
      return super.toString() + " -> " + getA().getId();
   }
}

ExportSchema.java

Code:

package fr.mycompany.hibernate;

import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

public class ExportSchema {

   public static void main(String[] args) {
      Configuration configuration = new Configuration().configure();
      SchemaExport schemaExport = new SchemaExport(configuration);
      schemaExport.create(true, true);
   }
}

HibernateUtil.java

Code:

package fr.mycompany.hibernate;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

   private static final SessionFactory sessionFactory;
   static {
      try {
         sessionFactory = new Configuration().configure().buildSessionFactory();
      } catch (Throwable ex) {
         System.err.println("Initial SessionFactory creation failed." + ex);
         throw new ExceptionInInitializerError(ex);
      }
   }

   public static SessionFactory getSessionFactory() {
      return sessionFactory;
   }
}

Classe de test => MainAB.java

Code:

package fr.mycompany.hibernate.test;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;

import fr.mycompany.hibernate.ExportSchema;
import fr.mycompany.hibernate.HibernateUtil;
import fr.mycompany.hibernate.test.bo.A;
import fr.mycompany.hibernate.test.bo.B;
import fr.mycompany.hibernate.test.bo.BusinessObject;

public class MainAB {

   public static void main(String[] args) {
      ExportSchema.main(null);

      A a = new A();
      B b = new B();
      a.setRelationB(b);

      System.err.println("<!-- Save Begin -->");
      save(a);
      System.err.println("<!-- Save End -->");

      List<? extends BusinessObject> bos = null;

      System.out.println("\n###################### A retrieve/list");
      bos = listBusinessObject(A.class);
      System.err.println("---------------------- A asString");
      System.err.println(bos.iterator().next().asString());

      System.out.println("\n###################### B retrieve/list");
      bos = listBusinessObject(B.class);
      System.err.println("---------------------- B asString");
      System.err.println(bos.iterator().next().asString());
   }

   public static void save(BusinessObject boToSave) {
      Session session = HibernateUtil.getSessionFactory().openSession();
      Transaction transaction = null;
      try {
         transaction = session.beginTransaction();
         if (boToSave != null) {
            session.saveOrUpdate(boToSave);
         }
         session.flush();
         transaction.commit();
      } catch (HibernateException e) {
         transaction.rollback();
         e.printStackTrace();
         throw e;
      } finally {
         session.close();
      }
   }

   @SuppressWarnings({ "finally", "unchecked" })
   public static <T> List<T> listBusinessObject(Class<T> boClass) {
      List<T> objects = null;

      Session session = HibernateUtil.getSessionFactory().openSession();
      Transaction transaction = null;
      try {
         transaction = session.beginTransaction();
         objects = session.createQuery("from " + boClass.getSimpleName()).list();
         transaction.commit();
      } catch (HibernateException e) {
         transaction.rollback();
         e.printStackTrace();
         throw e;
      } finally {
         //         Session not closed to allow lazy loading in the Main method         
         //         session.close();
         return objects;
      }
   }
}

Here is the output :

Quote:

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
alter table A drop foreign key FK418D4C45E8
alter table ADDRESS drop foreign key FKE66327D4D12962EC
alter table HOUSE drop foreign key FK41BCF0017066CE
drop table if exists A
drop table if exists ADDRESS
drop table if exists B
drop table if exists HOUSE
drop table if exists PERSON
create table A (ID bigint not null auto_increment, OBJ_OPT_LOCK datetime not null, b_ID bigint, primary key (ID)) ENGINE=InnoDB
create table ADDRESS (ID bigint not null auto_increment, OBJ_OPT_LOCK datetime not null, ADDRESSNAME varchar(255) not null, person_ID bigint, primary key (ID)) ENGINE=InnoDB
create table B (ID bigint not null auto_increment, OBJ_OPT_LOCK datetime not null, primary key (ID)) ENGINE=InnoDB
create table HOUSE (ID bigint not null auto_increment, OBJ_OPT_LOCK datetime not null, HOUSENAME varchar(255) not null, owner_ID bigint, primary key (ID)) ENGINE=InnoDB
create table PERSON (ID bigint not null auto_increment, OBJ_OPT_LOCK datetime not null, PERSONNAME varchar(255) not null, primary key (ID), unique (PERSONNAME)) ENGINE=InnoDB
alter table A add index FK418D4C45E8 (b_ID), add constraint FK418D4C45E8 foreign key (b_ID) references B (ID)
alter table ADDRESS add index FKE66327D4D12962EC (person_ID), add constraint FKE66327D4D12962EC foreign key (person_ID) references PERSON (ID)
alter table HOUSE add index FK41BCF0017066CE (owner_ID), add constraint FK41BCF0017066CE foreign key (owner_ID) references PERSON (ID)

Hibernate: insert into B (OBJ_OPT_LOCK) values (?)
Hibernate: insert into A (b_ID, OBJ_OPT_LOCK) values (?, ?)


###################### A retrieve/list
Hibernate: select a0_.ID as ID8_, a0_.b_ID as b3_8_, a0_.OBJ_OPT_LOCK as OBJ2_8_ from A a0_
Hibernate: select b0_.ID as ID9_1_, b0_.OBJ_OPT_LOCK as OBJ2_9_1_, a1_.ID as ID8_0_, a1_.b_ID as b3_8_0_, a1_.OBJ_OPT_LOCK as OBJ2_8_0_ from B b0_ left outer join A a1_ on b0_.ID=a1_.b_ID where b0_.ID=?
Hibernate: select a0_.ID as ID8_1_, a0_.b_ID as b3_8_1_, a0_.OBJ_OPT_LOCK as OBJ2_8_1_, b1_.ID as ID9_0_, b1_.OBJ_OPT_LOCK as OBJ2_9_0_ from A a0_ left outer join B b1_ on a0_.b_ID=b1_.ID where a0_.b_ID=?
---------------------- A asString
fr.lactalis.hibernate.test.bo.A@109b2a51 -> 1

###################### B retrieve/list
Hibernate: select b0_.ID as ID9_, b0_.OBJ_OPT_LOCK as OBJ2_9_ from B b0_
Hibernate: select a0_.ID as ID8_1_, a0_.b_ID as b3_8_1_, a0_.OBJ_OPT_LOCK as OBJ2_8_1_, b1_.ID as ID9_0_, b1_.OBJ_OPT_LOCK as OBJ2_9_0_ from A a0_ left outer join B b1_ on a0_.b_ID=b1_.ID where a0_.b_ID=?
---------------------- B asString
fr.lactalis.hibernate.test.bo.B@782cbc86 -> 1

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VincentLH

Post subject: Re: One-to-one - bidirectional - not lazy - N+1 select problem

Posted: Tue Sep 06, 2011 9:41 am

Newbie

Joined: Mon Sep 05, 2011 11:27 am
Posts: 4

I finally understand a part of my problem !
Here is the link http://stackoverflow.com/questions/2931936/hibernate-noob-fetch-join-problem

To sum up, it comes from how I am quering the DB:
I should use

Code:

objects = session.createCriteria(boClass).list();

instead of

Code:

objects = session.createQuery("from " + boClass.getSimpleName()).list();

I think when you are text writting the query or part of the query then you need to write join in the query.

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