[英]Hibernate HQL returns stale data?
我的Hibernate HQL查詢似乎正在返回陳舊的數據。
我有一個名為Account的簡單Java類,該類的實例映射到具有兩個varchar列(用戶名和姓氏)的單個數據庫表中。
如果我運行HQL查詢,例如:
List<?> accountList = session.createQuery("from Account where surname is null").list();
我按預期方式獲得了一個Account對象列表(表中的某些行確實具有空姓氏字段)。
然后,我將返回對象上的姓氏設置為一些非null值:
Iterator<?> accountIter = accountList.iterator();
while (accountIter.hasNext()) {
Account account = (Account) accountIter.next();
log("Adding surname of Jones to : " + account.getUsername());
account.setSurname("Jones");
}
在這一點上,如果我再次運行HQL查詢,我希望返回一個空的List(因為所有姓氏均應為非null),但取回的對象與第一次運行查詢時相同。 這不是我所期望的。
引用Hibernate文檔:
http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html_single/
“絕對不能保證會話何時執行JDBC調用,僅保證執行順序。但是,Hibernate保證Query.list(..)絕不會返回陳舊或不正確的數據。”
這似乎與我的代碼的行為相反。 查看下面清單4中的程序輸出,SQL Update語句發生在所有select語句之后,因此最后一個select返回錯誤的數據。 誰能說明正在發生的事情或我做錯了什么?
如果我用事務將姓氏的設置括起來,並執行session.saveOrUpdate(account)
則所有操作都可以,但是我認為這不是必需的。
我希望我的代碼在可能的情況下僅處理域類,並盡可能避免持久性代碼。
我在Java 1.6中使用Hibernate 4.1.8.Final
我的完整代碼清單如下:
清單1:Main.java:
package uk.ac.york.cserv.hibernatetest;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class Main {
private static SessionFactory sf;
Session session;
public static void main(String[] args) {
Main main = new Main();
main.doExample();
}
public Main() {
sf = new Configuration()
.configure("hibernate-ora.cfg.xml")
.buildSessionFactory();
session = sf.openSession();
}
public void closeSession() {
session.flush();
session.close();
}
public List<?> getAccountList() {
return session.createQuery("from Account where surname is null").list();
}
public void printAccountList(List<?> accountList) {
Iterator<?> accountIter = accountList.iterator();
while (accountIter.hasNext()) {
System.out.println(accountIter.next());
}
}
public void log(String msg) {
System.out.println(msg);
}
public void doExample() {
log("Print all accounts with null surnames...");
printAccountList(getAccountList());
log("Adding surnames to accounts that have null surnames...");
//session.beginTransaction();
Iterator<?> accountIter = getAccountList().iterator();
while (accountIter.hasNext()) {
Account account = (Account) accountIter.next();
log("Adding surname of Jones to : " + account.getUsername());
account.setSurname("Jones");
//session.saveOrUpdate(account);
}
//session.getTransaction().commit();
log("Again print all accounts that have null surnames (should be none)...");
printAccountList(getAccountList());
closeSession();
}
}
清單2:Account.java:
package uk.ac.york.cserv.hibernatetest;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name="ACCOUNTS")
public class Account {
@Id
@Column(name = "USERNAME", unique = true, nullable = false)
private String username;
@Column(name = "SURNAME")
private String surname;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getSurname() {
return surname;
}
public void setSurname(String surname) {
this.surname = surname;
}
@Override
public String toString() {
return "Account [username=" + username + ", surname=" + surname + "]";
}
}
清單3:Hibernate-ora.cfg.xml:
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@testhost:1521:test</property>
<property name="connection.username">testschema</property>
<property name="connection.password">testpassword</property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.Oracle10gDialect</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>
<!-- Names of the annotated classes -->
<mapping class="uk.ac.york.cserv.hibernatetest.Account"/>
</session-factory>
</hibernate-configuration>
清單4:該程序的輸出:
Print all accounts with null surnames...
Hibernate: select account0_.USERNAME as USERNAME0_, account0_.SURNAME as SURNAME0_ from ACCOUNTS account0_ where account0_.SURNAME is null
Account [username=user2, surname=null]
Adding surnames to accounts that have null surnames...
Hibernate: select account0_.USERNAME as USERNAME0_, account0_.SURNAME as SURNAME0_ from ACCOUNTS account0_ where account0_.SURNAME is null
Adding surname of Jones to : user2
Again print all accounts that have null surnames (should be none)...
Hibernate: select account0_.USERNAME as USERNAME0_, account0_.SURNAME as SURNAME0_ from ACCOUNTS account0_ where account0_.SURNAME is null
Account [username=user2, surname=Jones]
Hibernate: update ACCOUNTS set SURNAME=? where USERNAME=?
您描述的Hibernate行為沒有什么奇怪的
“在這一點上,如果我再次運行HQL查詢,我希望返回一個空列表(因為所有姓氏均應為非null),但是我會返回與第一次運行查詢時相同的對象這不是我所期望的。”
到那時,當您再次運行HQL查詢時,到目前為止您還沒有做任何與數據庫有關的事情。 這就是為什么您獲取所謂的“過時”數據,但實際上它是表中仍未修改的最新版本的原因
如果發出saveOrUpdate命令並關閉事務,則您在Java類中所做的更改將保留到數據庫中,以便新的HQL查詢執行顯示更新后的數據
我認為您誤解了Hibernate在此用例中的工作方式。 正是因為“ Hibernate保證Query.list(..)絕不會返回陳舊或錯誤的數據。” 您會看到來自數據庫的數據的更新版本,從數據庫的角度來看,您在Java類中所做的更改是“過時的”更改,並被來自原始的仍未修改的源的新的“新鮮”真實數據代替
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