Java – hibernate noob fetch join problem
•
Java
I have two classes test2 and test3 Test2 has a property test3, which is an instance of test3 In other words, I have a one-way onetoone Association, and test2 has a reference test3
When I select test2 from the database, I can see that the separate selection is to get the details of the relevant test3 class This is the famous 1 N selection problem
To solve this problem, I use a select. I try to use the fetch = join annotation, which I understand as @ fetch (fetchmode. Join)
However, with the addition of capture settings, I still see separate options The following are the relevant parts of my settings
hibernate. cfg. In XML:
<property name="max_fetch_depth">2</property>
Test 2:
public class Test2 {
@OneToOne (cascade=CascadeType.ALL,fetch=FetchType.EAGER)
@JoinColumn (name="test3_id")
@Fetch(FetchMode.JOIN)
public Test3 getTest3() {
return test3;
}
NB I set the fetchtype to Eagle. Even though it defaults to Eagle onetoone mapping, there is no difference
Thank you for any help!
Editor: I almost gave up using fetchmode Join – anyone can confirm that they have a job, that is, generate a left outer connection? In the document, I see "usually, the mapping document is not used for custom extraction, but retains the default behavior and uses the left connection extraction in HQL to replace a specific transaction"
If I do a left join extraction instead:
query = session. createQuery(“from Test2 t2 left join fetch t2.test3”);
Then I do get the result I want - the left outer join in the query
Edit No. 2:
Guys, thank you very much for your reply Now I think about it I usually find that when I investigate something, I will eventually learn more than I thought
I've learned one thing - I'm running the old hibernate because I didn't realize that the Maven repository is out of date Now I'm also bound to the JBoss repository. I have the latest version of hibernate and Hibernate annotations - 3.5 in both cases 1-Final.
I've set up a small test case to simplify it as much as possible - I still see 3.5 I'm 99% sure it's just a stupid problem in 1-final. I didn't set it right, especially Ross, because you got its work (thank you for taking the time to try it)
So I have these classes (the full text of this time)
Class A
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;
}
}
Class B
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;
}
}
My whole 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>
Test class
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;
}
}
Finally, the log output shows additional choices to return the associated class
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,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
Edit number 3:
If I do things the way Ross loads, the left outer connection is created If I use a list, separate selections are issued Here are the relevant codes Only by changing can behavioral differences be reproduced:
/* 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());
I think this may be called a "bug" As I mentioned earlier, in the document, they say that the extraction mode in HQL is usually specified rather than in the mapping. I think this may mean that there is more traffic in HQL to prevent it?
(add an additional 'name' field to a and B by me, otherwise hibernate optimizes the retrieval because it can get all B from a's foreign key)
Solution
I'm very interested in the code for another answer, because this is what I saw when testing the code you displayed, which generates two choices from test2
I use the following dependencies:
> org. hibernate：hibernate-entitymanager：jar：3.4. 0.GA：compile > org. hibernate：ejb3-persistence：jar：1.0. 2.GA：compile > org. hibernate：hibernate-commons-annotations：jar：3.1. 0.GA：compile > org. hibernate：hibernate-annotations：jar：3.4. 0.GA：compile > org. hibernate：hibernate-core：jar：3.3. 0.SP1：compile
If you use hibernate annotations because hibernate annotations override the EJB 3 extraction option, this has no impact See 2.4.1 5.1. Lazy options and fetching modes.
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