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Hibernate学习2 - 懒加载（延迟加载）、动态SQL参数、缓存
2022-06-24 19:46:00 【嗯嗯**】
文章目录
懒加载 == 默认开启懒加载
概述
懒加载： 当Bean对象在代码层面设置了级联查询即 一对多、多对多、多对一的关系，查询某个Bean时，不会发送两条SQL，而是只发送一条SQL，当代码需要访问该Bean的级联数据时，在发送获取级联数据SQL。
代码 == lazy属性值
one-to-many标签
概述
true/false
SysUser.java
@Getter
@Setter
public class SysUser extends BaseEntity {
private static final long serialVersionUID = 2095940921263481761L;
Set<Article> articles;
/** 用户昵称 - 如果没有设置昵称直接使用账户名显示 */
private String nickName;
/** 头像图片地址 */
private String headUrl;
/** 账户 */
private String loginName;
/** 密码 */
private String password;
/** 手机号 */
private String phoneNumber;
/** 邮箱 */
private String email;
/** 性别 */
private Integer gender;
/** 个性签名 */
private String personalMotto;
/** 最近登录时间 - 格式 - yyyyMMddHHmmss */
private String lastLoginTime;
/** 登录状态：0未登录 1单设备登陆 2多设备登陆 */
private Integer loginStatus;
/** 账户禁用状态：0账户可使用 1账户不可使用（封号） */
private Integer disabledStatus;
@Override
public String toString() {
return "SysUser{" +
"nickName='" + nickName + '\'' +
", headUrl='" + headUrl + '\'' +
", loginName='" + loginName + '\'' +
", password='" + password + '\'' +
", phoneNumber='" + phoneNumber + '\'' +
", email='" + email + '\'' +
", gender=" + gender +
", personalMotto='" + personalMotto + '\'' +
", lastLoginTime='" + lastLoginTime + '\'' +
", loginStatus=" + loginStatus +
", disabledStatus=" + disabledStatus +
'}';
}
}
Article.java
@NoArgsConstructor
@AllArgsConstructor
@Builder
@Accessors(chain = true)
@Data
public class Article extends BaseEntity {
private static final long serialVersionUID = -4714261187453073302L;
private SysUser sysUser;
/** 文章标题 */
private String title;
/** 文章内容 */
private String content;
private String abbreviationContent;
/** 文章被查看次数 */
private Integer checkNum;
/** 当前文章被点赞数 */
private Integer likeNum;
/** 当前文章不喜欢数 */
private Integer notLikeNum;
/** 文章是否违规：0未违规 1违规 - 违规不可显示 */
private Integer isViolation;
/** 创建者 - 冗余字段 - user表的nickName */
private String createBy;
/**列表文章的图片显示 - 如果指定则使用指定的图片（功能未做），没有指定则使用文章第一张图片，在没有则使用文章中有图标则使用目录分裂的图片*/
private String imgUrl;
/**文章内部图片*/
private String imgUrls;
/**文章内容类型：1富文本 2Markdown 3留空*/
private String type;
/**文章状态；-1违规 0草稿 1发布且公开 2发布且私密*/
private String status;
}
SysUser.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>
<class name="top.linruchang.entity.SysUser" table="sys_user">
<id name="id" type="java.lang.String">
<column name="id"></column>
<!--插入时，如果你没有设置ID，会帮你自动添加ID-->
<generator class="uuid"></generator>
</id>
<property name="headUrl" type="java.lang.String">
<column name="head_url" ></column>
</property>
<property name="loginName" type="java.lang.String">
<column name="login_name" ></column>
</property>
<!--默认是开启懒加载，测试时自行切换查看效果-->
<set name="articles" table="article" lazy="false">
<key column="user_id"></key>
<one-to-many class="top.linruchang.entity.Article"></one-to-many>
</set>
</class>
</hibernate-mapping>
Article.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>
<class name="top.linruchang.entity.Article" table="article">
<id name="id" type="java.lang.String">
<column name="id" ></column>
<!--插入时，如果你没有设置ID，会帮你自动添加ID-->
<generator class="uuid"></generator>
</id>
<!--<property name="userId" type="java.lang.String">-->
<!-- <column name="user_id"></column>-->
<!--</property>-->
<property name="title" type="java.lang.String">
<column name="title"></column>
</property>
<property name="content" type="java.lang.String">
<column name="content"></column>
</property>
<property name="likeNum" type="java.lang.Integer">
<column name="like_num"></column>
</property>
<!--默认是开启懒加载，测试时自行切换查看效果，如果这里显示lazy=true则会报错-->
<many-to-one lazy="false" name="sysUser" column="user_id" class="top.linruchang.entity.SysUser" />
</class>
</hibernate-mapping>
MyTest2.java
public class MyTest2 {
@SneakyThrows
public static void main(String[] args) {
new Thread(() -> {
Configuration configure = new Configuration().configure();
//获取sessionFactory
SessionFactory sessionFactory = configure.buildSessionFactory();
//获取数据库连接session
Session session = sessionFactory.openSession();
SysUser sysUser = session.find(SysUser.class, "6d72c93aa292cf2ca2e789919a5e7bdc");
System.out.println(sysUser);
}).start();
Thread.sleep(10000);
}
}
extra
比true/fasle属性更加懒惰的一种加载方式，或者可以说更加智能的一样加载方式，如果你只需要集合的长度，hibernate会查count而不是查整个数据集，当你使用到数据时，在会查数据集*
SysUser.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>
<class name="top.linruchang.entity.SysUser" table="sys_user">
<id name="id" type="java.lang.String">
<column name="id"></column>
<!--插入时，如果你没有设置ID，会帮你自动添加ID-->
<generator class="uuid"></generator>
</id>
<property name="headUrl" type="java.lang.String">
<column name="head_url" ></column>
</property>
<property name="loginName" type="java.lang.String">
<column name="login_name" ></column>
</property>
<!--更加懒惰的加载方式开启-->
<set name="articles" table="article" lazy="extra">
<key column="user_id"></key>
<one-to-many class="top.linruchang.entity.Article"></one-to-many>
</set>
</class>
</hibernate-mapping>
测试
@Test
public void test6() throws InterruptedException {
Configuration configure = new Configuration().configure();
//获取sessionFactory
SessionFactory sessionFactory = configure.buildSessionFactory();
//获取数据库连接session
Session session = sessionFactory.openSession();
SysUser sysUser = session.find(SysUser.class, "6d72c93aa292cf2ca2e789919a5e7bdc");
System.out.println(sysUser.getArticles().size());
System.out.println("============================");
System.out.println(sysUser.getArticles());
}
many-to-one标签
概述
<?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>
<class name="top.linruchang.entity.Article" table="article">
<id name="id" type="java.lang.String">
<column name="id" ></column>
<!--插入时，如果你没有设置ID，会帮你自动添加ID-->
<generator class="uuid"></generator>
</id>
<!--<property name="userId" type="java.lang.String">-->
<!-- <column name="user_id"></column>-->
<!--</property>-->
<property name="title" type="java.lang.String">
<column name="title"></column>
</property>
<property name="content" type="java.lang.String">
<column name="content"></column>
</property>
<property name="likeNum" type="java.lang.Integer">
<column name="like_num"></column>
</property>
<!-- 自己去调整这个属性，默认是开启了懒加载模式的 -->
<many-to-one lazy="no-proxy" name="sysUser" column="user_id" class="top.linruchang.entity.SysUser" />
</class>
</hibernate-mapping>
many-to-many标签 == 跟 one-to-many一样
概述
<?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>
<class name="top.linruchang.entity.MyOrder2" table="my_order">
<id name="id" type="java.lang.String">
<column name="id"></column>
<!--插入时，如果你没有设置ID，会帮你自动添加ID-->
<generator class="uuid"></generator>
</id>
<property name="name" type="java.lang.String">
<column name="name"></column>
</property>
<property name="money" type="java.lang.String">
<column name="money"></column>
</property>
<!-- 这里进行设置懒加载-->
<set name="myUser2" table="user_order_rel" lazy="extra">
<key column="my_order_id" ></key>
<many-to-many column="my_user_id" class="top.linruchang.entity.MyUser2"></many-to-many>
</set>
</class>
</hibernate-mapping>
动态SQL参数 = 默认不开启
insert = 跟MyBatisPlus一样，属性字段是空则该字段不会出现在SQL中
update = 跟MyBatisPlus不一样，根据缓存的对象来判断属性字段是否需要出现在SQL中，属性字段缓存值与当前对象不一致则出现在SQL，否则不出现
Article.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">
<!-- package：类似mybatis的Bean别名type-aliases-package这个属性，用于有些属性不用写全限定名-->
<!-- default-lazy：默认启动懒加载，即一对多，多对多，多对一关系上使用-->
<!-- auto-import：默认true，是否可以在查询语句中使用非全限定名，如果项目中有两个同名的Bean，最好在两个映射文件中设置为false-->
<hibernate-mapping package="top.linruchang.entity" default-lazy="true" auto-import="false" >
<!-- dynamic-insert dynamic-update：默认都为false。true时类似 mybatisplus的代码插入Java语句，只要属性是空则update、insert的SQL语句就不会出现该列 -->
<class name="Article" table="article" dynamic-insert="true" dynamic-update="true">
<id name="id" type="java.lang.String">
<column name="id" ></column>
<!--插入时，如果你没有设置ID，会帮你自动添加ID-->
<generator class="uuid"></generator>
</id>
<!--<property name="userId" type="java.lang.String">-->
<!-- <column name="user_id"></column>-->
<!--</property>-->
<property name="title" type="java.lang.String">
<column name="title"></column>
</property>
<property name="content" type="java.lang.String">
<column name="content"></column>
</property>
<property name="likeNum" type="java.lang.Integer">
<column name="like_num"></column>
</property>
<many-to-one lazy="no-proxy" name="sysUser" column="user_id" class="SysUser" />
</class>
</hibernate-mapping>
测试程序
@Test
public void test6() {
Configuration configure = new Configuration().configure();
SessionFactory sessionFactory = configure.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
//查到的结果会被session缓存
Article article = session.find(Article.class, "4028b88178e54c750178e54c77c80000");
System.out.println(article);
// 动态update=true情况下：拿上面的缓存与当前对象做比较
article.setTitle("放到沙发上对方的身份==");
session.saveOrUpdate(article);
//如果使用这样，最后会save的，因为判断是否需要insert、update是根据缓存去看的
// Article updateArticle = new Article();
// updateArticle.setId(article.getId())
// updateArticle.setContent("fdsfdsfsd");
// session.saveOrUpdate(updateArticle);
transaction.commit();
session.close();
}
未开启动态更新SQL
开启动态更新SQL
缓存
一级缓存Session级别 = 默认开启
@Test
public void test6() {
Configuration configure = new Configuration().configure();
SessionFactory sessionFactory = configure.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Article article = session.find(Article.class, "4028b88178e54c750178e54c77c80000");
System.out.println(article);
Article article2 = session.find(Article.class, "4028b88178e54c750178e54c77c80000");
System.out.println(article2);
transaction.commit();
session.close();
}
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