hibernate之优化抓取(选择抓取策略之通过子查询预抓取集合--实例)

最新推荐文章于 2025-07-28 23:27:29 发布

fhd001

最新推荐文章于 2025-07-28 23:27:29 发布

阅读量592

点赞数

CC 4.0 BY-SA版权

分类专栏： hibernate 文章标签： hibernate 优化 string user null class

本文链接：https://blog.youkuaiyun.com/fhd001/article/details/5946297

hibernate 专栏收录该内容

129 篇文章

订阅专栏

本文介绍了一个使用Hibernate框架的示例项目配置，通过在集合属性上设置fetch=subselect来实现子查询预抓取功能，从而优化了关联对象的加载过程。

该实例主要用于集合，如：<set>,在<set>上添加属性：fetch="subselect"，表示子查询预抓取。

----------

pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>hibernateTest</groupId> <artifactId>hibernateTest</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <name>hibernateTest</name> <url>http://maven.apache.org</url> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <type>jar</type> <scope>test</scope> <optional>false</optional> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-core</artifactId> <version>3.3.1.GA</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-nop</artifactId> <version>1.5.2</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>javassist</groupId> <artifactId>javassist</artifactId> <version>3.4.GA</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>c3p0</groupId> <artifactId>c3p0</artifactId> <version>0.9.1</version> <type>jar</type> <optional>false</optional> </dependency> <dependency> <groupId>com.oracle</groupId> <artifactId>ojdbc14</artifactId> <version>10.2.0.3.0</version> <type>jar</type> <scope>runtime</scope> <optional>false</optional> </dependency> </dependencies> <build> <finalName>hibernateTest</finalName> <resources> <resource> <directory>src/main/resources</directory> </resource> <resource> <directory>src/main/java</directory> <excludes> <exclude>**/*.java</exclude> </excludes> </resource> </resources> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.6</source> <target>1.6</target> <encoding>UTF-8</encoding> </configuration> </plugin> </plugins> </build> </project>

resources/hibernate.cfg.xml:

<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory name="sessionFactory">  <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>  <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:XE</property> <property name="hibernate.connection.useUnicode">true</property> <property name="hibernate.connection.characterEncoding">gbk</property>  <property name="hibernate.connection.username">system</property>  <property name="hibernate.connection.password">password</property>  <property name="hibernate.c3p0.max_size">20</property>  <property name="hibernate.c3p0.min_size">5</property>  <property name="hibernate.c3p0.timeout">120</property>  <property name="hibernate.c3p0.max_statements">100</property>  <property name="hibernate.c3p0.idle_test_period">120</property>  <property name="hibernate.c3p0.acquire_increment">2</property>  <property name="dialect">org.hibernate.dialect.OracleDialect</property>  <property name="show_sql">true</property>  <property name="hibernate.format_sql">true</property>  <property name="hibernate.use_identifier_rollback">true</property>  <mapping resource="pojo/User.hbm.xml" /> <mapping resource="pojo/Book.hbm.xml" /> </session-factory> </hibernate-configuration>

pojo/User.java:

package pojo; import java.io.Serializable; import java.util.Date; import java.util.HashSet; import java.util.Set; public class User implements Serializable { private String id; private String name; private String password; //时间戳 private Date updateTime; private Set<Book> bookSet = new HashSet<Book>(); public String getId() { return id; } @SuppressWarnings("unused") private void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public Set<Book> getBookSet() { return bookSet; } public void setBookSet(Set<Book> bookSet) { this.bookSet = bookSet; } //添加 public void addBook(Book b){ this.bookSet.add(b); b.setUser(this); } public Date getUpdateTime() { return updateTime; } }

pojo/User.hbm.xml:

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="pojo"> <class name="User" table="A_USER" dynamic-insert="true" dynamic-update="true"> <id name="id" column="ID" type="string"> <generator class="uuid.hex" /> </id> <timestamp name="updateTime" access="field" column="UPDATETIME" source="db"/> <property name="name" column="NAME" type="string" /> <property name="password" column="PASSWORD" type="string" />  <set name="bookSet" cascade="all" inverse="true" lazy="extra" fetch="subselect"> <key column="USER_ID" not-null="true"/> <one-to-many class="Book"/> </set> </class> </hibernate-mapping>

pojo/Book.java:

package pojo; import java.io.Serializable; import java.util.Date; public class Book implements Serializable { private String id; private String bookName; private String bookDesc; //时间戳 private Date updateTime; private User user; public String getId() { return id; } @SuppressWarnings("unused") private void setId(String id) { this.id = id; } public String getBookName() { return bookName; } public void setBookName(String bookName) { this.bookName = bookName; } public String getBookDesc() { return bookDesc; } public void setBookDesc(String bookDesc) { this.bookDesc = bookDesc; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } public Date getUpdateTime() { return updateTime; } //重写hashCode() @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((bookDesc == null) ? 0 : bookDesc.hashCode()); result = prime * result + ((bookName == null) ? 0 : bookName.hashCode()); result = prime * result + ((id == null) ? 0 : id.hashCode()); result = prime * result + ((updateTime == null) ? 0 : updateTime.hashCode()); return result; } //重写equals() @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Book other = (Book) obj; if (bookDesc == null) { if (other.bookDesc != null) return false; } else if (!bookDesc.equals(other.bookDesc)) return false; if (bookName == null) { if (other.bookName != null) return false; } else if (!bookName.equals(other.bookName)) return false; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; if (updateTime == null) { if (other.updateTime != null) return false; } else if (!updateTime.equals(other.updateTime)) return false; return true; } }

pojo/Book.hbm.xml:

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="pojo"> <class name="Book" table="A_BOOK" dynamic-insert="true" dynamic-update="true"> <id name="id" column="ID" type="string"> <generator class="uuid.hex" /> </id> <timestamp name="updateTime" access="field" column="UPDATETIME" source="db"/> <property name="bookName" column="BOOKNAME" type="string"/> <property name="bookDesc" column="BOOKDESC" type="string"/> <many-to-one name="user" column="USER_ID" class="User" not-null="true"/> </class> </hibernate-mapping>

util/HibernateUtil.java:

package util; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; public class HibernateUtil { private static SessionFactory sessionFactory; static{ try { sessionFactory = new Configuration().configure().buildSessionFactory(); } catch (Throwable e) { throw new ExceptionInInitializerError(e); } } public static SessionFactory getSessionFactory(){ return sessionFactory; } public static void shutdown(){ getSessionFactory().close(); } }

util/Manager.java:

package util; import java.util.Iterator; import java.util.List; import org.hibernate.Session; import org.hibernate.Transaction; import pojo.Book; import pojo.User; public class Manager { @SuppressWarnings("rawtypes") public static void main(String[] args) { Session session = HibernateUtil.getSessionFactory().openSession(); Transaction transaction = session.beginTransaction(); List userList = session.createQuery("from User").list(); User u = null; for(int i=0;i<userList.size();i++){ u = (User) userList.get(i); Iterator<Book> iter = u.getBookSet().iterator(); Book b = null; while(iter.hasNext()){ b = iter.next(); System.out.println("bookName: " + b.getBookName()); } } transaction.commit(); session.close(); } }

输出日志：

Hibernate: select user0_.ID as ID0_, user0_.UPDATETIME as UPDATETIME0_, user0_.NAME as NAME0_, user0_.PASSWORD as PASSWORD0_ from A_USER user0_ Hibernate: select bookset0_.USER_ID as USER5_1_, bookset0_.ID as ID1_, bookset0_.ID as ID1_0_, bookset0_.UPDATETIME as UPDATETIME1_0_, bookset0_.BOOKNAME as BOOKNAME1_0_, bookset0_.BOOKDESC as BOOKDESC1_0_, bookset0_.USER_ID as USER5_1_0_ from A_BOOK bookset0_ where bookset0_.USER_ID in ( select user0_.ID from A_USER user0_ ) bookName: b6 bookName: b1 bookName: b7 bookName: b2 bookName: b4 bookName: b5 bookName: b3 bookName: b8 bookName: bbbttt2 bookName: bbbttt1 bookName: bbbttt2 bookName: bbbttt3 bookName: bbbttt4 bookName: bbbttt5 bookName: bbbttt6 bookName: bbbttt6 bookName: bbbttt7 bookName: bbbttt7