Почему Hibernate генерирует CROSS JOIN для неявного объединения ассоциации @ManyToOne?

Question

Baur & Кинг сказал в своей книге:

неявные объединений всегда направлен вдоль многие к одному или один-к-одному ассоциации, никогда через коллекцию многозначных ассоциации.

[P 646, Ch 14]

Но когда я делаю, что в коде он генерируя CROSS JOIN вместо INNER JOIN.

Картография от Member2 (много-к-одному) ->CLub.

Но Club2 не имеет информации о членах, а Member2 имеет внешний ключ Club2.

Мой запрос

// Implicit: Find all UK club member who is female 
Transaction t1 = HibernateUtil.begin(); 
Query query = 
    HibernateUtil.getSession().createQuery("From Member2 m where m.club2.country = 'UK' "); 
List<Member2> memList = query.list(); 
for (Member2 m : memList) 
    System.out.println(m); 
HibernateUtil.end(t1); 

И, Hibernate генерирует следующий SQL-запрос:

Hibernate: 
    select 
     member2x0_.member_id as member_i1_1_, 
     member2x0_.club_id as club_id5_1_, 
     member2x0_.member_age as member_a2_1_, 
     member2x0_.member_name as member_n3_1_, 
     member2x0_.member_sex as member_s4_1_ 
    from 
     TBL_MEMBER2 member2x0_ cross 
    join 
     TBL_CLUB2 club2x1_ 
    where 
     member2x0_.club_id=club2x1_.club_id 
     and club2x1_.country='UK' 
Hibernate: 
    select 
     club2x0_.club_id as club_id1_0_0_, 
     club2x0_.club_name as club_nam2_0_0_, 
     club2x0_.country as country3_0_0_ 
    from 
     TBL_CLUB2 club2x0_ 
    where 
     club2x0_.club_id=? 
aaa 25 m 
bbb 28 f 

Club2.java

package com.lilu.de.onetomany.uni.other; 

import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.GenerationType; 
import javax.persistence.Id; 
import javax.persistence.SequenceGenerator; 
import javax.persistence.Table; 

@Entity 
@Table(name = "TBL_CLUB2") 
public class Club2 { 

    @GeneratedValue(generator = "pkey_Club2", strategy = GenerationType.SEQUENCE) 
    @SequenceGenerator(name = "pkey_Club2", initialValue = 1000, allocationSize = 10, 
     sequenceName = "seq_pkey_Club2") 
    @Id 
    private int club_id; 

    private String club_name; 

    private String country; 

    // private Set Member2 = new HashSet(); 

    public Club2() { 
    super(); 
    } 

    public Club2(String cname, String ccountry) { 
    this.club_name = cname; 
    this.country = ccountry; 
    } 

    @Override 
    public String toString() { 
    String temp = club_name + " " + country + " "; 
    // Iterator<Member2> iter = Member2.iterator(); 
    // String mems = null; 
    // while (iter.hasNext()) { 
    // mems += iter.next(); 
    // } 
    // temp += "\n" + mems; 
    return temp; 
    } 

    public int getClub_id() { 
    return club_id; 
    } 

    public void setClub_id(int club_id) { 
    this.club_id = club_id; 
    } 

    public String getClub_name() { 
    return club_name; 
    } 

    public void setClub_name(String club_name) { 
    this.club_name = club_name; 
    } 

    public String getCountry() { 
    return country; 
    } 

    public void setCountry(String country) { 
    this.country = country; 
    } 

    /* 
    * public Set<Member2> getMember2() { return Member2; } 
    * 
    * public void setMember2(Set<Member2> Member2) { this.Member2 = Member2; } 
    */ 
} 

Member2.java

package com.lilu.de.onetomany.uni.other; 

import javax.persistence.CascadeType; 
import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.GenerationType; 
import javax.persistence.Id; 
import javax.persistence.JoinColumn; 
import javax.persistence.ManyToOne; 
import javax.persistence.SequenceGenerator; 
import javax.persistence.Table; 

@Entity 
@Table(name = "TBL_MEMBER2") 
public class Member2 { 

    @GeneratedValue(generator = "pkey_member2", strategy = GenerationType.SEQUENCE) 
    @SequenceGenerator(name = "pkey_member2", sequenceName = "seq_pkey_member2") 
    @Id 
    private int member_id; 

    private String member_name; 

    private int member_age; 

    private char member_sex; 

    @ManyToOne(cascade = CascadeType.ALL) 
    @JoinColumn(name = "club_id") 
    private Club2 club2; 

    public Member2() { 
    super(); 
    } 

    public Member2(String mname, int age, char sex) { 
    this.member_name = mname; 
    this.member_age = age; 
    this.member_sex = sex; 
    } 

    public Club2 getClub2() { 
    return club2; 
    } 

    public void setClub2(Club2 club2) { 
    this.club2 = club2; 
    } 

    @Override 
    public String toString() { 
    return member_name + " " + member_age + " " + member_sex; 
    } 

    public String getMember_name() { 
    return member_name; 
    } 

    public void setMember_name(String member_name) { 
    this.member_name = member_name; 
    } 

    public int getMember_age() { 
    return member_age; 
    } 

    public void setMember_age(int member_age) { 
    this.member_age = member_age; 
    } 

    public char getMember_sex() { 
    return member_sex; 
    } 

    public void setMember_sex(char member_sex) { 
    this.member_sex = member_sex; 
    } 

    public int getMember_id() { 
    return member_id; 
    } 

    public void setMember_id(int member_id) { 
    this.member_id = member_id; 
    } 

} 

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?> 
<!-- 
    ~ Hibernate, Relational Persistence for Idiomatic Java 
    ~ 
    ~ Copyright (c) 2010, Red Hat Inc. or third-party contributors as 
    ~ indicated by the @author tags or express copyright attribution 
    ~ statements applied by the authors. All third-party contributions are 
    ~ distributed under license by Red Hat Inc. 
    ~ 
    ~ This copyrighted material is made available to anyone wishing to use, modify, 
    ~ copy, or redistribute it subject to the terms and conditions of the GNU 
    ~ Lesser General Public License, as published by the Free Software Foundation. 
    ~ 
    ~ This program is distributed in the hope that it will be useful, 
    ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
    ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License 
    ~ for more details. 
    ~ 
    ~ You should have received a copy of the GNU Lesser General Public License 
    ~ along with this distribution; if not, write to: 
    ~ Free Software Foundation, Inc. 
    ~ 51 Franklin Street, Fifth Floor 
    ~ Boston, MA 02110-1301 USA 
    --> 
<!DOCTYPE hibernate-configuration PUBLIC 
     "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 
     "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> 

<hibernate-configuration> 

    <session-factory> 

     <!-- Database connection settings --> 
     <property name="connection.driver_class">org.postgresql.Driver</property> 
     <property name="connection.url">jdbc:postgresql://localhost:5432/hibernatedb1</property> 
     <property name="connection.username">postgres</property> 
     <property name="connection.password">ani155</property> 

     <!-- JDBC connection pool (use the built-in) --> 
     <property name="connection.pool_size">1</property> 

     <!-- SQL dialect --> 
     <property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property> 

     <!-- Disable the second-level cache --> 
     <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property> 

     <!-- Echo all executed SQL to stdout --> 
     <property name="show_sql">true</property> 
     <property name="format_sql">true</property> 

     <!-- Drop and re-create the database schema on startup --> 
     <property name="hbm2ddl.auto">update</property> 

     <!-- Names the annotated entity class --> 
     <mapping class="com.lilu.de.onetomany.uni.other.Club2"/> 
     <mapping class="com.lilu.de.onetomany.uni.other.Member2"/> 
     <!-- <mapping class="com.apal.mapping.onetoone.User"/> --> 
    </session-factory> 

</hibernate-configuration> 

Test.java

package com.lilu.de.onetomany.uni.other; 

import java.util.List; 

import org.hibernate.Query; 
import org.hibernate.Session; 
import org.hibernate.SessionFactory; 
import org.hibernate.Transaction; 
import org.hibernate.cfg.Configuration; 

public class Test { 
    public static void main(String[] args) { 

    Test test = new Test(); 
    // test.setup(); 
    test.SelectQuery1Implicit(); 
    // test.SelectQuery2ExplicitFromClause(); 
    // test.SelectQuery3JoinFetch(); 
    // test.SelectQuery4ThetaJoin(); 
    } 

    private void SelectQuery1Implicit() { 
    // Implicit: Find all UK club member who is female 
    Transaction t1 = HibernateUtil.begin(); 
    Query query = 
     HibernateUtil.getSession().createQuery("From Member2 m where m.club2.country = 'UK' "); 
    List<Member2> memList = query.list(); 
    for (Member2 m : memList) 
     System.out.println(m); 
    HibernateUtil.end(t1); 
    } 

    private void setup() { 
    Transaction t1 = HibernateUtil.begin(); 
    Club2 c1 = new Club2("MulaRougne", "UK"); 
    Member2 m1 = new Member2("aaa", 25, 'm'); 
    Member2 m2 = new Member2("bbb", 28, 'f'); 
    m1.setClub2(c1); 
    m2.setClub2(c1); 
    HibernateUtil.getSession().save(c1); 
    HibernateUtil.getSession().save(m1); 
    HibernateUtil.getSession().save(m2); 
    Club2 c2 = new Club2("Queen's Club", "UK"); 
    Club2 c3 = new Club2("Disney", "USA"); 
    Member2 m3 = new Member2("ccc", 32, 'm'); 
    Member2 m4 = new Member2("ddd", 23, 'm'); 
    m3.setClub2(c3); 
    m4.setClub2(c3); 
    HibernateUtil.getSession().save(m3); 
    HibernateUtil.getSession().save(m4); 
    HibernateUtil.getSession().save(c2); 
    HibernateUtil.getSession().save(c3); 


    /* 
    * Club2 c1 = new Club2("MulaRougne", "UK"); Club2 c2 = new Club2("Queen's Club", "UK"); Club2 
    * c3 = new Club2("Disney", "USA"); 
    * 
    * Member2 m1 = new Member2("aaa", 25, 'm'); Member2 m2 = new Member2("bbb", 28, 'f'); Member2 
    * m3 = new Member2("ccc", 32, 'm'); Member2 m4 = new Member2("ddd", 23, 'm'); Member2 m5 = new 
    * Member2("ee", 30, 'f'); 
    * 
    * c1.getMember2().add(m1); c1.getMember2().add(m2); c1.getMember2().add(m3); 
    * 
    * c2.getMember2().add(m4); c2.getMember2().add(m5); 
    * 
    * HibernateUtil.getSession().save(c2); HibernateUtil.getSession().save(m4); 
    * HibernateUtil.getSession().save(m5); 
    * 
    * HibernateUtil.getSession().save(c1); HibernateUtil.getSession().save(m1); 
    * HibernateUtil.getSession().save(m2); HibernateUtil.getSession().save(m3); 
    */ 
    HibernateUtil.end(t1); 
    } 


    private static class HibernateUtil { 
    private static SessionFactory factory; 
    private static Session session; 
    static { 
     factory = new Configuration().configure().buildSessionFactory(); 
    } 

    public static Session getSession() { 
     return session; 
    } 

    public static Transaction begin() { 
     session = factory.openSession(); 
     return session.beginTransaction(); 
    } 

    public static void end(Transaction tran) { 
     tran.commit(); 
    } 
    } 
} 

Answer 1

Большинство СУБД оптимизирует перекрестное соединение с ИНЕКЕ к РЕГИСТРИРУЙТЕСЬ в любом случае, но я предпочитаю всегда использовать явные JOIN и вместо.

перекрестное соединение порождается implicit JOIN:

where m.club2.country = 'UK' 

Чтобы избежать второго запроса клуба вы можете написать запрос следующим образом:

Query query = HibernateUtil.getSession().createQuery(
     "select m " + 
     "from Member2 m " + 
     "join fetch m.club2 c" + 
     "where " + 
     " c.country = :country " 
) 
.setParameter("country", "UK"); 

Этот запрос удалит CROSS JOIN и вторичный выбор при использовании параметров привязки вместо жестко закодированных.