休眠noob获取连接问题

Question

我有两个类，Test2和Test3。 Test2有一个属性test3，它是Test3的一个实例。换句话说，我有一个单向OneToOne关联，test2引用了test3。

当我从db中选择Test2时，我可以看到正在做一个单独的选择来获取关联的test3类的详细信息。这是着名的1 + N选择问题。

为了解决这个问题使用单一的选择，我想使用fetch =加入注解，我的理解是@Fetch（FetchMode.JOIN）语句

然而，取指令集的加入，我还是见单独的选择。下面是我设置的相关部分..

的hibernate.cfg.xml：

<property name="max_fetch_depth">2</property> 

的Test2：

public class Test2 { 
@OneToOne (cascade=CascadeType.ALL , fetch=FetchType.EAGER) 
@JoinColumn (name="test3_id") 
@Fetch(FetchMode.JOIN) 
public Test3 getTest3() { 
    return test3; 
} 

NB我设置FetchType为EAGER出于绝望，即使它无论如何，OneToOne映射默认为EAGER，但它没有区别。

感谢您的帮助！

编辑：我几乎已经放弃尝试使用FetchMode.JOIN - 任何人都可以确认他们已经得到它的工作，即产生一个左外连接？ 在文档中我看到：“通常，映射文档不用于自定义提取，而是保留默认行为，并使用HQL中的左连接提取替代特定事务。”

如果我确实代替左连接取指：

query = session.createQuery（“from Test2 t2 left join fetch t2.test3”）;

然后我确实得到了我想要的结果 - 即查询中的左外连接。

编辑号2：

，大家好，非常感谢你为你的答复。现在我想深究这一点。我通常会发现，当我调查一些事情时，我最终会比我想象的要多得多。

我已经学会了一件事 - 我在旧版的hibernate上运行，因为我没有意识到maven存储库已过时。现在我已经连接到jboss存储库了，并且在两种情况下，我都有最新版本的hibernate和hibernate注释 - 3.5.1-Final。

我已经设置了一个小测试用例，尽可能简化它 - 我仍然在3.5中看到这个问题。1 - 决赛，我'99％肯定这只是一些愚蠢的我没有设置正确，尤其是罗斯，因为你得到它的工作（谢谢花时间尝试顺便说一句）

所以我有这些类（全文这段时间）

A类

package com.play.hibernate2; 

import javax.persistence.CascadeType; 
import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.Id; 
import javax.persistence.OneToOne; 

import org.hibernate.annotations.Fetch; 
import org.hibernate.annotations.FetchMode; 

@Entity 
public class A { 

    private Integer id; 
    private B b; 

    public A() { 
     super(); 
    } 

    @Id 
    @GeneratedValue 
    public Integer getId() { 
     return id; 
    } 

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

    @OneToOne (cascade=CascadeType.ALL) 
    @Fetch(FetchMode.JOIN) 
    public B getB() { 
     return b; 
    } 

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

B类

package com.play.hibernate2; 

import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.Id; 

@Entity 
public class B { 

    private Integer id; 

    public B() { 
     super(); 
    } 

    @Id 
    @GeneratedValue 
    public Integer getId() { 
     return id; 
    } 

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

我的整个的hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?> 
<!DOCTYPE hibernate-configuration PUBLIC 
     "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 
     "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> 

<hibernate-configuration> 

    <session-factory> 

     <!-- Database connection settings --> 
     <property name="connection.driver_class">com.mysql.jdbc.Driver</property> 
     <!-- <property name="connection.driver_class">com.p6spy.engine.spy.P6SpyDriver</property> --> 
     <property name="connection.url">jdbc:mysql://localhost:3306/play</property> 
     <property name="connection.username">play</property> 
     <property name="connection.password">play</property> 

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

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

     <!-- Enable Hibernate's automatic session context management --> 
     <property name="current_session_context_class">thread</property> 

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

     <!-- Echo all executed SQL to stdout --> 
     <property name="show_sql">true</property> 
     <property name="generate_statistics">true</property> 
     <!-- 
     <property name="cache.use_structured_entries">true</property> 
     <property name="cache.use_query_cache">true</property> 
     --> 
     <property name="format_sql">true</property> 
     <property name="use_sql_comments">true</property> 

     <!-- I think this may fix my individual requests for OneToOne problem --> 
     <property name="max_fetch_depth">2</property> 
     <!-- <property name="default_batch_fetch_size">10</property> --> 

    </session-factory>  

</hibernate-configuration> 

测试类

package com.play.hibernate2; 

import java.util.List; 
import java.util.Map; 


import org.hibernate.FlushMode; 
import org.hibernate.Query; 
import org.hibernate.Session; 
import org.hibernate.SessionFactory; 
import org.hibernate.cfg.AnnotationConfiguration; 
import org.hibernate.tool.hbm2ddl.SchemaExport; 

public class RunTests4 { 
    private SessionFactory sessionFactory; 

    public static void main(String[] args){ 
     RunTests4 d = new RunTests4(); 
     d.run3(); 
    } 
    public void run3(){ 

     Session session = getSession(); 
     session.beginTransaction(); 

     createEntities(session); 

     session.getTransaction().commit(); 

     System.out.println("NOW WITH A NEW TRANSACTION"); 
     session = getSession(); 
     session.beginTransaction(); 

     Query query = session.createQuery("from A"); 
     List results = query.list(); 
     for (int i=0; i<results.size(); i++){ 
      System.out.println("Row "+i+" was:"); 
      A a = (A)results.get(i); 
      System.out.println("Result "+i); 
      System.out.println(a.toString()); 
     } 

     session.getTransaction().commit(); 


    } 
    public void createEntities(Session session){ 
     for (int i=0; i<2; i++){ 
      A a = new A(); 

      B b = new B(); 

      a.setB(b); 

      session.save(a); 

     } 

    } 
    public Session getSession(){ 
     if (sessionFactory == null){ 
      AnnotationConfiguration config = new AnnotationConfiguration(); 
      config.addAnnotatedClass(A.class); 
      config.addAnnotatedClass(B.class); 
      config.configure(); 
      new SchemaExport(config).create(true,true); 

      sessionFactory = config.buildSessionFactory(); 
     } 
     Session session = sessionFactory.getCurrentSession(); 

     return session; 
    } 

} 

最后的日志输出，显示额外的选择取回相关类

2 [main] INFO org.hibernate.cfg.annotations.Version - Hibernate Annotations 3.5.1-Final 
23 [main] INFO org.hibernate.cfg.Environment - Hibernate 3.5.1-Final 
28 [main] INFO org.hibernate.cfg.Environment - hibernate.properties not found 
32 [main] INFO org.hibernate.cfg.Environment - Bytecode provider name : javassist 
37 [main] INFO org.hibernate.cfg.Environment - using JDK 1.4 java.sql.Timestamp handling 
160 [main] INFO org.hibernate.annotations.common.Version - Hibernate Commons Annotations 3.2.0.Final 
176 [main] INFO org.hibernate.cfg.Configuration - configuring from resource: /hibernate.cfg.xml 
176 [main] INFO org.hibernate.cfg.Configuration - Configuration resource: /hibernate.cfg.xml 
313 [main] INFO org.hibernate.cfg.Configuration - Configured SessionFactory: null 
338 [main] INFO org.hibernate.dialect.Dialect - Using dialect: org.hibernate.dialect.MySQLDialect 
462 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.Test2 
545 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.Test2 on table Test2 
649 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.Test3 
650 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.Test3 on table Test3 
651 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.A 
651 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.A on table A 
653 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.B 
653 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.B on table B 
678 [main] INFO org.hibernate.cfg.AnnotationConfiguration - Hibernate Validator not found: ignoring 
687 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - Running hbm2ddl schema export 
688 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - exporting generated schema to database 
691 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Using Hibernate built-in connection pool (not for production use!) 
691 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Hibernate connection pool size: 1 
698 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - autocommit mode: false 
711 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - using driver: com.mysql.jdbc.Driver at URL: jdbc:mysql://localhost:3306/play 
711 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - connection properties: {user=play, password=****} 

    alter table A 
     drop 
     foreign key FK412E010759 

    alter table Test2 
     drop 
     foreign key FK4CF5DC04B7E1B79 

    drop table if exists A 

    drop table if exists B 

    drop table if exists Test2 

    drop table if exists Test3 

    create table A (
     id integer not null auto_increment, 
     b_id integer, 
     primary key (id) 
    ) 

    create table B (
     id integer not null auto_increment, 
     primary key (id) 
    ) 

    create table Test2 (
     id integer not null auto_increment, 
     name varchar(255), 
     value integer not null, 
     test3_id integer, 
     primary key (id) 
    ) 

    create table Test3 (
     id integer not null auto_increment, 
     name varchar(255), 
     value integer not null, 
     primary key (id) 
    ) 

    alter table A 
     add index FK412E010759 (b_id), 
     add constraint FK412E010759 
     foreign key (b_id) 
     references B (id) 

    alter table Test2 
     add index FK4CF5DC04B7E1B79 (test3_id), 
     add constraint FK4CF5DC04B7E1B79 
     foreign key (test3_id) 
     references Test3 (id) 
2562 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - schema export complete 
2564 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - cleaning up connection pool: jdbc:mysql://localhost:3306/play 
2571 [main] INFO org.hibernate.cfg.search.HibernateSearchEventListenerRegister - Unable to find org.hibernate.search.event.FullTextIndexEventListener on the classpath. Hibernate Search is not enabled. 
2575 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Using Hibernate built-in connection pool (not for production use!) 
2575 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Hibernate connection pool size: 1 
2575 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - autocommit mode: false 
2575 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - using driver: com.mysql.jdbc.Driver at URL: jdbc:mysql://localhost:3306/play 
2575 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - connection properties: {user=play, password=****} 
2622 [main] INFO org.hibernate.cfg.SettingsFactory - RDBMS: MySQL, version: 5.1.30 
2622 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC driver: MySQL-AB JDBC Driver, version: mysql-connector-java-5.1.9 (Revision: ${svn.Revision}) 
2633 [main] INFO org.hibernate.dialect.Dialect - Using dialect: org.hibernate.dialect.MySQLDialect 
2635 [main] INFO org.hibernate.engine.jdbc.JdbcSupportLoader - Disabling contextual LOB creation as JDBC driver reported JDBC version [3] less than 4 
2636 [main] INFO org.hibernate.transaction.TransactionFactoryFactory - Using default transaction strategy (direct JDBC transactions) 
2638 [main] INFO org.hibernate.transaction.TransactionManagerLookupFactory - No TransactionManagerLookup configured (in JTA environment, use of read-write or transactional second-level cache is not recommended) 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - Automatic flush during beforeCompletion(): disabled 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - Automatic session close at end of transaction: disabled 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC batch size: 15 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC batch updates for versioned data: disabled 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - Scrollable result sets: enabled 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC3 getGeneratedKeys(): enabled 
2638 [main] INFO org.hibernate.cfg.SettingsFactory - Connection release mode: auto 
2639 [main] INFO org.hibernate.cfg.SettingsFactory - Maximum outer join fetch depth: 2 
2639 [main] INFO org.hibernate.cfg.SettingsFactory - Default batch fetch size: 1 
2639 [main] INFO org.hibernate.cfg.SettingsFactory - Generate SQL with comments: enabled 
2639 [main] INFO org.hibernate.cfg.SettingsFactory - Order SQL updates by primary key: disabled 
2639 [main] INFO org.hibernate.cfg.SettingsFactory - Order SQL inserts for batching: disabled 
2639 [main] INFO org.hibernate.cfg.SettingsFactory - Query translator: org.hibernate.hql.ast.ASTQueryTranslatorFactory 
2641 [main] INFO org.hibernate.hql.ast.ASTQueryTranslatorFactory - Using ASTQueryTranslatorFactory 
2641 [main] INFO org.hibernate.cfg.SettingsFactory - Query language substitutions: {} 
2641 [main] INFO org.hibernate.cfg.SettingsFactory - JPA-QL strict compliance: disabled 
2641 [main] INFO org.hibernate.cfg.SettingsFactory - Second-level cache: enabled 
2641 [main] INFO org.hibernate.cfg.SettingsFactory - Query cache: disabled 
2644 [main] INFO org.hibernate.cfg.SettingsFactory - Cache region factory : org.hibernate.cache.impl.bridge.RegionFactoryCacheProviderBridge 
2644 [main] INFO org.hibernate.cache.impl.bridge.RegionFactoryCacheProviderBridge - Cache provider: org.hibernate.cache.NoCacheProvider 
2644 [main] INFO org.hibernate.cfg.SettingsFactory - Optimize cache for minimal puts: disabled 
2644 [main] INFO org.hibernate.cfg.SettingsFactory - Structured second-level cache entries: disabled 
2648 [main] INFO org.hibernate.cfg.SettingsFactory - Echoing all SQL to stdout 
2648 [main] INFO org.hibernate.cfg.SettingsFactory - Statistics: enabled 
2649 [main] INFO org.hibernate.cfg.SettingsFactory - Deleted entity synthetic identifier rollback: disabled 
2649 [main] INFO org.hibernate.cfg.SettingsFactory - Default entity-mode: pojo 
2649 [main] INFO org.hibernate.cfg.SettingsFactory - Named query checking : enabled 
2649 [main] INFO org.hibernate.cfg.SettingsFactory - Check Nullability in Core (should be disabled when Bean Validation is on): enabled 
2697 [main] INFO org.hibernate.impl.SessionFactoryImpl - building session factory 
2796 [Finalizer] INFO org.hibernate.connection.DriverManagerConnectionProvider - cleaning up connection pool: jdbc:mysql://localhost:3306/play 
2929 [main] INFO org.hibernate.impl.SessionFactoryObjectFactory - Not binding factory to JNDI, no JNDI name configured 
Hibernate: 
    /* insert com.play.hibernate2.B 
     */ insert 
     into 
      B 

     values 
      () 
Hibernate: 
    /* insert com.play.hibernate2.A 
     */ insert 
     into 
      A 
      (b_id) 
     values 
      (?) 
Hibernate: 
    /* insert com.play.hibernate2.B 
     */ insert 
     into 
      B 

     values 
      () 
Hibernate: 
    /* insert com.play.hibernate2.A 
     */ insert 
     into 
      A 
      (b_id) 
     values 
      (?) 
NOW WITH A NEW TRANSACTION 
Hibernate: 
    /* 
from 
    A */ select 
     a0_.id as id2_, 
     a0_.b_id as b2_2_ 
    from 
     A a0_ 
Hibernate: 
    /* load com.play.hibernate2.B */ select 
     b0_.id as id3_0_ 
    from 
     B b0_ 
    where 
     b0_.id=? 
Hibernate: 
    /* load com.play.hibernate2.B */ select 
     b0_.id as id3_0_ 
    from 
     B b0_ 
    where 
     b0_.id=? 
Row 0 was: 
Result 0 
com.play.hibernate2.A@351daa0e 
Row 1 was: 
Result 1 
com.play.hibernate2.A@2e879860 

编辑号码3：

如果我做的事情罗斯的方式，与负载，一个左外连接被创建。如果我用一个列表来做，就会发出单独的选择。这是相关的代码。只有改变这种行为才能重现差异：

/* generates the left outer join 
    A a = (A)session.load(A.class,1); 
    System.out.println(a.getId()+" = "+a.getB().getName()); 
    */ 

    // Creates separate selects for each object b associated with each a 
    Query query = session.createQuery("from A"); 
    List results = query.list(); 
    A a = (A)results.get(0); 
    System.out.println(a.getId()+" = "+a.getB().getName()); 

我想它可能被称为'错误'。正如我前面提到的，在文档中，他们说在HQL中而不是在映射中指定获取模式是'平常的'，我认为这可能意味着HQL方式已经有更多的人流量来处理它。 。？

（顺便说一下我增加了一个额外的“名称”字段A和B，否则冬眠优化了检索，因为它可以只是从一个外键让所有B的）

Answer 1

当我从数据库中选择的Test2，我可以看到一个单独的选择正在取得了解详细内容相关的test3类。

我对对方的回答的代码很感兴趣，因为这是我所看到过的测试代码时，你正在展示，它生成两个选择了from Test2。

我用下面的依赖关系：

• org.hibernate作为：休眠-的EntityManager：罐子：3.4.0.GA：编译
• org.hibernate作为：EJB3持久性：罐子：1.0。 2.GA:compile
• org.hibernate作为：休眠公地的注解：罐子：3.1.0.GA：编译
• org.hibernate作为：冬眠的注解：罐子：3.4.0.GA：编译
• org.hibernate：hibernate-core：jar：3.3.0.SP1：compile

我将FetchType设置为EAGER超出了绝望，即使它对OneToOne映射默认为EAGER，但它没有区别。

如果您使用Hibernate注释，因为Hibernate注释会覆盖EJB3抓取选项，所以这没有影响。请参阅2.4.5.1. Lazy options and fetching modes。

Answer 2

我创建了一个非常简单的应用测试你得到的场景和你的代码应该工作（它对我有用）。我试过的唯一的事情会给我多个select语句，将max_fetch_depth设置为0.如果设置为2（或未配置），我在我的查询中获得左外连接。你使用的是什么版本的hibernate？我正在使用3.4.0.GA.

编辑： 下面是简单的应用程序我用（与帕斯卡提到的相同版本）：

CFG：

<hibernate-configuration> 
    <session-factory> 
     <property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property> 
     <property name="hibernate.connection.url">jdbc:hsqldb:hibscribs</property> 
     <property name="hibernate.connection.username">sa</property> 
     <property name="hibernate.connection.password"></property> 
     <property name="hibernate.dialect">org.hibernate.dialect.HSQLDialect</property> 
     <property name="show_sql">true</property> 
     <property name="format_sql">true</property> 
     <property name="hbm2ddl.auto">create-drop</property> 
     <property name="current_session_context_class">thread</property> 
     <!-- property name="max_fetch_depth">0</property--><!-- uncomment to see where 2 selects are used instead of join --> 

     <mapping class="com.mydomain.bo.Person" /> 
     <mapping class="com.mydomain.bo.Phone" /> 

    </session-factory> 
</hibernate-configuration> 

Person实体 - 保持它的简单只有@OneToOne，加JoinColumn等没有任何区别。

@Entity 
@Table(name="person") 
public class Person { 
    private Long id; 
    private String name; 
    private Phone phone; 

    @Id 
    public Long getId() { 
     return id; 
    } 
    public void setId(Long id) { 
     this.id = id; 
    } 

    public String getName() { 
     return name; 
    } 
    public void setName(String name) { 
     this.name = name; 
    } 

    @OneToOne(cascade=CascadeType.ALL) 
    public Phone getPhone() { 
     return phone; 
    } 

    public void setPhone(Phone phone) { 
     this.phone = phone; 
    } 
} 

。

@Entity 
@Table(name="phone") 
public class Phone { 
    private Long id; 
    private String number; 

    @Id 
    public Long getId() { 
     return id; 
    } 
    public void setId(Long id) { 
     this.id = id; 
    } 

    public String getNumber() { 
     return number; 
    } 
    public void setNumber(String number) { 
     this.number = number; 
    } 
} 

简单的测试：

SessionFactory session = HibernateUtil.getSessionFactory(); 
Session sess = session.getCurrentSession(); 
Transaction tx = sess.beginTransaction(); 

Phone phone = new Phone(); 
phone.setId(1L); 
phone.setNumber("1234567"); 

Person person = new Person(); 
person.setId(1L); 
person.setName("Bob"); 
person.setPhone(phone); 

sess.save(person); 

tx.commit(); 

sess = session.openSession(); 

//Person p1 = (Person)sess.load(Person.class,1L); 
//System.out.println(p1.getPhone().getNumber()); 

// changed the above code to use the Criteria interface below: 
Criteria criteria = sess.createCriteria(Person.class); 
List<Person> results = criteria.list(); 
for (int i=0; i<results.size(); i++){ 
    Person p = (Person)results.get(i); 
    System.out.println(p.getPhone().getNumber()); 
} 

输出：

Hibernate: 
    select 
     phone_.id, 
     phone_.number as number1_ 
    from 
     phone phone_ 
    where 
     phone_.id=? 
Hibernate: 
    insert 
    into 
     phone 
     (number, id) 
    values 
     (?, ?) 
Hibernate: 
    insert 
    into 
     person 
     (name, phone_id, id) 
    values 
     (?, ?, ?) 
Hibernate: 
    select 
     person0_.id as id0_1_, 
     person0_.name as name0_1_, 
     person0_.phone_id as phone3_0_1_, 
     phone1_.id as id1_0_, 
     phone1_.number as number1_0_ 
    from 
     person person0_ 
    left outer join 
     phone phone1_ 
      on person0_.phone_id=phone1_.id 
    where 
     person0_.id=? 
1234567 

Answer 3

作为蒸馏：如果您使用的查询界面（例如：session.createQuery（））

@Fetch（JOIN）将被忽略，但它如果使用标准接口可以正常使用。

这实际上是Hibernate中一个从未解决的错误。这很不幸，因为很多应用程序都使用Query接口，并且无法轻松迁移到Criteria接口。

如果使用Query接口，则必须手动将JOIN FETCH语句添加到HQL中。