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主流 ORM 框架 Object Relation Mapping 对象关系映射，将面向对象映射成面向关系。

一、如何使用

1、导入相关依赖
2、创建 Hibernate 配置文件
3、创建实体类
4、创建实体类-关系映射文件
5、调用 Hibernate API 完成操作

二、具体操作

1、创建 Maven 工程，pom.xml

<dependencies><!--简化实体类的开发--><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.10</version></dependency><!--java连接mysql依赖--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.16</version></dependency><!--Hibernate依赖--><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-core</artifactId><version>5.4.10.Final</version></dependency>
</dependencies>

2、hibernate.cfg.xml

核心配置：session-factory

SessionFactory：针对单个数据库映射经过编译的内存镜像文件，将数据库转换为⼀个 Java 可以识别的镜像文件。

构建 SessionFactory 非常耗费资源，所以通常⼀个工程只需要创建⼀个 SessionFactory。

<?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><!--配置数据源--><property name="connection.username">root</property><property name="connection.password">password</property><property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property><property name="connection.url">jdbc:mysql://localhost:3306/hibernate?serverTimezone=Asia/Shanghai&amp;useUnicode=true&amp;characterEncoding=UTF-8</property><!--C3P0连接池--><property name="hibernate.c3p0.acquire_increment">10</property><property name="hibernate.c3p0.idle_test_period">10000</property><property name="hibernate.c3p0.timeout">5000</property><property name="hibernate.c3p0.max_size">30</property><property name="hibernate.c3p0.min_size">5</property><property name="hibernate.c3p0.max_statements">10</property><!--是否输出底层SQL语句--><property name="hibernate.show_sql">true</property><!--输出底层SQL语句是否格式化--><property name="hibernate.format_sql">true</property><!--是否自动生成数据库--><!--update：如果已经有表，更新；如果没有，创建。（一般用这个）--><property name="hibernate.hbm2ddl.auto">update</property><!--数据库方言--><!--如果使用的mysql是5.x，写：org.hibernate.dialect.MySQL5Dialect。--><!--如果使用的mysql是8.x，写：org.hibernate.dialect.MySQL8Dialect。--><property name="hibernate.dialect">org.hibernate.dialect.MySQL8Dialect</property><!--注册实体关系映射文件--><mapping resource="com/htl/entity/People.hbm.xml"/><mapping resource="com/htl/entity/Customer.hbm.xml"/><mapping resource="com/htl/entity/Orders.hbm.xml"/><mapping resource="com/htl/entity/Account.hbm.xml"/><mapping resource="com/htl/entity/Course.hbm.xml"/></session-factory></hibernate-configuration>

3、创建实体类

package com.htl.entity;import lombok.Getter;
import lombok.Setter;import java.util.Set;@Getter
@Setter
public class Customer {private Integer id;private String name;private Set<Orders> orders;@Overridepublic String toString() {return "Customer{" +"id=" + id +", name='" + name + '\'' +'}';}
}

package com.htl.entity;import lombok.Getter;
import lombok.Setter;@Getter
@Setter
public class Orders {private Integer id;private String name;private Customer customer;@Overridepublic String toString() {return "Orders{" +"id=" + id +", name='" + name + '\'' +'}';}
}

4、创建实体关系映射文件

package com.htl.entity;import lombok.Data;@Data
public class People {private Integer id;private String name;private Double money;
}

People.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="com.htl.entity.People" table="people"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><property name="money" type="java.lang.Double"><column name="money"></column></property></class></hibernate-mapping>

5、实体关系映射文件注册到 Hibernate 的配置文件中。

<!--注册实体关系映射文件-->
<mapping resource="com/htl/entity/People.hbm.xml"></mapping>

6、使用 Hibernate API 完成数据操作。

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test {public static void main(String[] args) {// 创建ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*/System.out.println(configuration);// 获取SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();// 获取SessionSession session = sessionFactory.openSession();// 向People表中插入数据People people = new People();people.setName("李四");people.setMoney(200.0);session.save(people);/*保存*/session.beginTransaction().commit();/*提交事务*/session.close();/*关闭session*/}
}

7、pom.xml 中需要配置 resource

<!--配置 resource-->
<!--能够识别读取java里面的xml文件-->
<build><resources><resource><directory>src/main/java</directory><includes><include>**/*.xml</include></includes></resource></resources>
</build>

三、Hibernate 级联操作

1、一对多关系

客户和订单：每个客户可以购买多个产品，生成多个订单，但是一个订单只能属于一个客户，所以客户
是一，订单是多。

数据库中一的一方是主表，多的一方时候从表，通过主外键关系来维护。

面向对象中

package com.htl.entity;import lombok.Getter;
import lombok.Setter;import java.util.Set;@Getter
@Setter
public class Customer {private Integer id;private String name;private Set<Orders> orders;@Overridepublic String toString() {return "Customer{" +"id=" + id +", name='" + name + '\'' +'}';}
}

package com.htl.entity;import lombok.Getter;
import lombok.Setter;@Getter
@Setter
public class Orders {private Integer id;private String name;private Customer customer;@Overridepublic String toString() {return "Orders{" +"id=" + id +", name='" + name + '\'' +'}';}
}

2、多对多关系

学生选课：一门课程可以被多个学生选择，一个学生可以选择多门课程，学生是多，课程也是多。

数据库中是通过两个一对多关系来维护的，学生和课程都是主表，额外增加⼀张中间表作为从表，两张
主表和中间表都是一对多关系。

面向对象中

package com.htl.entity;import lombok.Getter;
import lombok.Setter;import java.util.Set;@Getter
@Setter
public class Account {private Integer id;private String name;private Set<Course> courses;@Overridepublic String toString() {return "Account{" +"id=" + id +", name='" + name + '\'' +'}';}
}

package com.htl.entity;import lombok.Getter;
import lombok.Setter;import java.util.Set;@Getter
@Setter
public class Course {private Integer id;private String name;private Set<Account> accounts;@Overridepublic String toString() {return "Course{" +"id=" + id +", name='" + name + '\'' +'}';}
}

Java 和数据库对于这两种关系的体现完全是两种不同的方式，Hibernate 框架的作用就是将这两种方式进行转换和映射。

四、Hibernate 实现一对多

Customer.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="com.htl.entity.Customer" table="customer"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><set name="orders" table="orders"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many></set></class> </hibernate-mapping>

• set 标签来配置实体类中的集合属性 orsers
• name 实体类属性名
• table 表名
• key 外键
• one-to-many 与集合泛型的实体类对应

Orders.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="com.htl.entity.Orders" table="orders"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><many-to-one name="customer" class="com.htl.entity.Customer" column="cid"></many-to-one></class> </hibernate-mapping>

• many-to-one 配置实体类对应的对象属性
• name 属性名
• class 属性对应的类
• column 外键

需要在 Hibernate 配置文件中进行注册

<!-- 注册实体关系映射⽂件 -->
<mapping resource="com/htl/entity/Customer.hbm.xml"></mapping>
<mapping resource="com/htl/entity/Orders.hbm.xml"></mapping>

Hibernate API

package com.htl.test;import com.htl.entity.Customer;
import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test2 {public static void main(String[] args) {//创建ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*///获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//创建CustomerCustomer customer = new Customer();customer.setName("张三11");//创建OrdersOrders orders = new Orders();orders.setName("订单11");//建立关联关系orders.setCustomer(customer);//保存session.save(customer);session.save(orders);//提交事务session.beginTransaction().commit();//关闭session.close();}
}

五、Hibernate 实现多对多

Account.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="com.htl.entity.Account" table="t_account"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><set name="courses" table="account_course"><key column="aid"></key><many-to-many class="com.htl.entity.Course" column="cid"></many-to-many></set></class> </hibernate-mapping>

Course.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="com.htl.entity.Course" table="t_course"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><set name="accounts" table="account_course"><key column="cid"></key><many-to-many class="com.htl.entity.Account" column="aid"></many-to-many></set></class> </hibernate-mapping>

• name 实体类对应的集合属性名
• table 中间表名
• key 外键
• many-to-many 与集合泛型的实体类对应
• column 属性与中间表的外键字段名对应

注册 Hibernate 配置文件中

<!--注册实体关系映射文件-->
<mapping resource="com/htl/entity/Account.hbm.xml"></mapping>
<mapping resource="com/htl/entity/Course.hbm.xml"></mapping>

Hibernate API

package com.htl.test;import com.htl.entity.Account;
import com.htl.entity.Course;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;import java.util.HashSet;
import java.util.Set;public class Test3 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*///获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Course course = new Course();course.setName("C语言");Account account = new Account();account.setName("李四");Set<Course> courses = new HashSet<Course>();courses.add(course);account.setCourses(courses);session.save(course);session.save(account);session.beginTransaction().commit();session.close();}
}

六、Hibernate 延迟加载

延迟加载、惰性加载、懒加载

使用延迟加载可以提⾼程序的运行效率，Java 程序与数据库交互的频次越低，程序运⾏的效率就越高，所以我们应该尽量减少 Java 程序与数据库的交互次数，Hibernate 延迟加载就很好的做到了这一点。

客户和订单，当我们查询客户对象时，因为有级联设置，所以会将对应的订单信息一并查询出来，这样就需要发送两条 SQL 语句，分别查询客户信息和订单信息。

延迟加载的思路是：当我们查询客户的时候，如果没有访问订单数据，只发送一条 SQL 语句查询客户信息，如果需要访问订单数据，则发送两条 SQLL。

延迟加载可以看作是⼀种优化机制，根据具体的需求，⾃动选择要执⾏的 SQL 语句数量。

1、一对多

1、查询 Customer，对 orders 进行延迟加载设置，在 customer.hbm.xml 进行设置，延迟加载默认开启。

<set name="orders" table="orders" lazy="true"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many>
</set>

2、查询 Customer

package com.htl.test;import com.htl.entity.Customer;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test4 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*///获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = session.get(Customer.class,6);System.out.println(customer);session.close();}
}

package com.htl.test;import com.htl.entity.Customer;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test4 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*///获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = session.get(Customer.class,6);System.out.println(customer.getOrders());session.close();}
}

在 customer.hbm.xml 中设置延迟加载关闭后

<set name="orders" table="orders" lazy="false"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many>
</set>

package com.htl.test;import com.htl.entity.Customer;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test4 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*///获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = session.get(Customer.class,6);System.out.println(customer);session.close();}
}

lazy 除了可以设置 true 和 false 之外，还可以设置 extra，extra 是比 true 更加懒惰的⼀种加载方式，或者说是更加智能的⼀种加载方式，通过例子看区别：

查询 Customer 对象，打印该对象对应的 orders 集合的长度。

在 customer.hbm.xml 中设置延迟加载为 extra 后。

<set name="orders" table="orders" lazy="extra"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many>
</set>

package com.htl.test;import com.htl.entity.Customer;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test4 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();/*如果默认是 hibernate.cfg.xml ，configure()里面就不用写。如果xml名字改了，里面就写修改的名字。*///获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = session.get(Customer.class,6);System.out.println(customer.getOrders().size());session.close();}
}

也可以通过 Orders 来设置 Customer 的延迟加载，orders.hbm.xml 中进⾏设置。

<many-to-one name="customer" class="com.htl.entity.Customer" column="cid" lazy="proxy"></many-to-one>

package com.htl.test;import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test5 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Orders orders = session.get(Orders.class,2);System.out.println(orders);session.close();}
}

package com.htl.test;import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test5 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Orders orders = session.get(Orders.class,2);System.out.println(orders.getCustomer());session.close();}
}

no-proxy：当调用方法需要访问 customer 的成员变量时，发送 SQL 语句查询 Customer，否则不查询。

proxy：无论调用方法是否需要访问 customer 的成员变量，都会发送 SQL 语句查询 Customer。

2、多对多

1、查询 Course，加载对应的 Account，默认延迟加载开启。

在 Course.hbm.xml 里面，lazy 设置为 true。不写默认为 true。

<set name="accounts" table="account_course" lazy="true"><key column="cid"></key><many-to-many class="com.htl.entity.Account" column="aid"></many-to-many>
</set>

package com.htl.test;import com.htl.entity.Course;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test6 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Course course = session.get(Course.class,1);System.out.println(course);session.close();}
}

package com.htl.test;import com.htl.entity.Course;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test6 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Course course = session.get(Course.class,1);System.out.println(course.getAccounts());session.close();}
}

在 Course.hbm.xml 里面，lazy 关闭，设置为 false 后，查看结果。

<set name="accounts" table="account_course" lazy="false"><key column="cid"></key><many-to-many class="com.htl.entity.Account" column="aid"></many-to-many>
</set>

package com.htl.test;import com.htl.entity.Course;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test6 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Course course = session.get(Course.class,1);System.out.println(course);session.close();}
}

2、查询 Account，加载对应的 Course，默认延迟加载开启。

在 Account.hbm.xml 里面，lazy 设置为 true。不写默认为 true。

<set name="courses" table="account_course" lazy="true"><key column="aid"></key><many-to-many class="com.htl.entity.Course" column="cid"></many-to-many>
</set>

package com.htl.test;import com.htl.entity.Account;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test7 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Account account = session.get(Account.class,1);System.out.println(account);session.close();}
}

package com.htl.test;import com.htl.entity.Account;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test7 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Account account = session.get(Account.class,1);System.out.println(account.getCourses());session.close();}
}

在 Account.hbm.xml 里面，lazy 关闭，设置为 false 后，查看结果。

<set name="courses" table="account_course" lazy="false"><key column="aid"></key><many-to-many class="com.htl.entity.Course" column="cid"></many-to-many>
</set>

package com.htl.test;import com.htl.entity.Account;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test7 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Account account = session.get(Account.class,1);System.out.println(account);session.close();}
}

七、Hibernate 配置文件

• hibernate.cfg.xml
• hbm.xml

1、Hibernate.cfg.xml

hibernate.cfg.xml 配置 Hibernate 的全局环境。

<?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><!--配置数据源--><property name="connection.username">root</property><property name="connection.password">password</property><property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property><property name="connection.url">jdbc:mysql://localhost:3306/hibernate?serverTimezone=Asia/Shanghai&amp;useUnicode=true&amp;characterEncoding=UTF-8</property><!--C3P0连接池--><property name="hibernate.c3p0.acquire_increment">10</property><property name="hibernate.c3p0.idle_test_period">10000</property><property name="hibernate.c3p0.timeout">5000</property><property name="hibernate.c3p0.max_size">30</property><property name="hibernate.c3p0.min_size">5</property><property name="hibernate.c3p0.max_statements">10</property><!--是否输出底层SQL语句--><property name="hibernate.show_sql">true</property><!--输出底层SQL语句是否格式化--><property name="hibernate.format_sql">true</property><!--是否自动生成数据库--><!--update：如果已经有表，更新；如果没有，创建。（一般用这个）--><property name="hibernate.hbm2ddl.auto">update</property><!--数据库方言--><!--如果使用的mysql是5.x，写：org.hibernate.dialect.MySQL5Dialect。--><!--如果使用的mysql是8.x，写：org.hibernate.dialect.MySQL8Dialect。--><property name="hibernate.dialect">org.hibernate.dialect.MySQL8Dialect</property><!--注册实体关系映射文件--><mapping resource="com/htl/entity/People.hbm.xml"/><mapping resource="com/htl/entity/Customer.hbm.xml"/><mapping resource="com/htl/entity/Orders.hbm.xml"/><mapping resource="com/htl/entity/Account.hbm.xml"/><mapping resource="com/htl/entity/Course.hbm.xml"/></session-factory></hibernate-configuration>

<1>、数据库的基本信息。

<property name="connection.username">root</property>
<property name="connection.password">password</property>
<property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/hibernate?serverTimezone=Asia/Shanghai&amp;useUnicode=true&amp;characterEncoding=UTF-8</property>

<2>、集成 C3P0，设置数据库连接池信息。

<property name="hibernate.c3p0.acquire_increment">10</property>
<property name="hibernate.c3p0.idle_test_period">10000</property>
<property name="hibernate.c3p0.timeout">5000</property>
<property name="hibernate.c3p0.max_size">30</property>
<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.max_statements">10</property>

<3>、Hibernate 基本信息

<!--是否输出底层SQL语句-->
<property name="hibernate.show_sql">true</property>
<!--输出底层SQL语句是否格式化-->
<property name="hibernate.format_sql">true</property>
<!--是否自动生成数据库-->
<!--update：如果已经有表，更新；如果没有，创建。（一般用这个）-->
<property name="hibernate.hbm2ddl.auto">update</property>
<!--数据库方言-->
<!--如果使用的mysql是5.x，写：org.hibernate.dialect.MySQL5Dialect。-->
<!--如果使用的mysql是8.x，写：org.hibernate.dialect.MySQL8Dialect。-->
<property name="hibernate.dialect">org.hibernate.dialect.MySQL8Dialect</property>

<-是否自动生成数据库->里面可填的几个值：

• update：动态创建表，如果表存在，则直接使用，如果表不存在，则创建。
• create：无论表是否存在，都会重新创建。
• create-drop：初始化创建表，程序结束时删除表。
• validate：校验实体关系映射文件和数据表是否对应，不能对应直接报错。

<4>、注册实体关系映射文件

<mapping resource="com/htl/entity/People.hbm.xml"></mapping>
<mapping resource="com/htl/entity/Customer.hbm.xml"></mapping>
<mapping resource="com/htl/entity/Orders.hbm.xml"></mapping>
<mapping resource="com/htl/entity/Account.hbm.xml"></mapping>
<mapping resource="com/htl/entity/Course.hbm.xml"></mapping>

2、hbm.xml

称为：实体关系映射文件

<?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="com.htl.entity.Course" table="t_course"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><set name="accounts" table="account_course" lazy="true"><key column="cid"></key><many-to-many class="com.htl.entity.Account" column="aid"></many-to-many></set></class> </hibernate-mapping>

<1>、hibernate-mapping 属性

• package：给 class 节点对应的实体类统一设置包名，此处设置包名，class 的 name 属性就可以省略包名。

如上面的实体映射文件修改为下面的：

  <?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="com.htl.entity"><class name="Course" table="t_course"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><set name="accounts" table="account_course" lazy="true"><key column="cid"></key><many-to-many class="Account" column="aid"></many-to-many></set></class> </hibernate-mapping>

• schema：数据库 schema 的名称。

• catalog：数据库 catalog 的名称。

• default-cascade：默认的级联关系，默认为 none。

• default-access：Hibernate 用来访问属性的策略。

• default-lazy：指定了未明确注明 lazy 属性的 Java 属性和集合类，Hibernate 会采用什么样的加载风格，默认为 true 。

• auto-import：指定我们是否可以在查询语句中使用非全限定类名，默认为 true，如果项目中有两个同名的持久化类，最好在这两个类的对应映射文件中配置为 false。

<2>、class 属性

• name：实体类名
• table：数据表名
• schema：数据库 schema 的名称，会覆盖 hibernate-mapping 的 schema
• catalog：数据库 catalog 的名称，会覆盖 hibernate-mapping 的 catalog
• proxy：指定⼀个接口，在延迟加载时作为代理使用
• dynamic-update：动态更新（默认关闭）
• dynamic-insert：动态添加（默认关闭）

当没有开启动态加载（dynamic-insert）时，只设置 name 的值，没有赋值的 money 也会默认赋 null 存入。两个都存。（有多少属性存多少属性）

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test8 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();People people = new People();people.setName("张三");session.save(people);session.close();}
}

当开启动态加载（dynamic-insert）后，只设置 name 的值，则只存 name ，其余不存：

<class name="com.htl.entity.People" table="people" dynamic-insert="true">

当没有开启动态更新（dynamic-update），更新 money 时，update语句连同 name 一块更新了。

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test8 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();People people = session.get(People.class,6);people.setMoney(2000.0);session.update(people);session.beginTransaction().commit();session.close();}
}

当开启动态更新（dynamic-update）后，更新 money 时，update语句不会连同 name 一块更新。

<class name="com.htl.entity.People" table="people" dynamic-insert="true" dynamic-update="true">

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test8 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();People people = session.get(People.class,7);people.setMoney(7000.0);session.update(people);session.beginTransaction().commit();session.close();}
}

• where：查询时给 SQL 添加 where 条件（默认关闭）

当没加 where 时：

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test8 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();String hql = "from People";Query query = session.createQuery(hql);List<People> list = query.list();for (People people :list) {System.out.println(people);}session.beginTransaction().commit();session.close();}
}

加了 where 后，可以用 where 约束查询结果。

<class name="com.htl.entity.People" table="people" dynamic-insert="true" dynamic-update="true" where="id = 6">

运行语句同上。

<3>、id 属性

• name：实体类属性名
• type：实体类属性数据类型

此处可以设置两种类型的数据：Java 数据类型或者 Hibernate 映射类型。

实体类的属性数据类型必须与数据表对应的字段数据类型一致：

int 对应 int，String 对应 varchar

如何进行映射？

Java 数据类型映射到 Hibernate 映射类型，再由 Hibernate 映射类型映射到 SQL 数据类型

Java —》Hibernate —〉SQL

• column：数据表的主键字段名
• generator：主键生成策略

1、hilo 算法

2、increment：Hibernate 自增

3、identity：数据库自增

4、native：本地策略，根据底层数据库自动选择主键的生成策略

5、uuid.hex 算法

6、select 算法

<4>、property 属性

• name：实体类的属性名
• column：数据表字段名
• type：数据类型
• update：该字段是否可以修改，默认为 true
• insert：该字段是否可以添加，默认为 true
• lazy：延迟加载策略

<5>、实体关系映射文件属性

1、inverse

inverse 属性是用来设置是否将维护权交给对方，默认是 false，不交出维护权，双方都在维护，将它设置为 true，表示放弃维护。

Customer 和 Orders 是一对多关系，一个 Customer 对应多个 Orders，实体类中用一个 set 集合来表示对应的 Orders。

package com.htl.entity;import lombok.Getter;
import lombok.Setter;import java.util.Set;@Getter
@Setter
public class Customer {private Integer id;private String name;private Set<Orders> orders;@Overridepublic String toString() {return "Customer{" +"id=" + id +", name='" + name + '\'' +'}';}
}

Customer.hbm.xml 中使用 set 标签来配置映射关系。

<?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="com.htl.entity.Customer" table="customer"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><set name="orders" table="orders" lazy="true"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many></set></class> </hibernate-mapping>

实体类

package com.htl.entity;import lombok.Getter;
import lombok.Setter;@Getter
@Setter
public class Orders {private Integer id;private String name;private Customer customer;@Overridepublic String toString() {return "Orders{" +"id=" + id +", name='" + name + '\'' +'}';}
}

Orders.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="com.htl.entity.Orders" table="orders"><id name="id" type="java.lang.Integer"><column name="id"></column><generator class="identity"></generator></id><property name="name" type="java.lang.String"><column name="name"></column></property><many-to-one name="customer" class="com.htl.entity.Customer" column="cid" lazy="proxy"></many-to-one></class> </hibernate-mapping>

package com.htl.test;import com.htl.entity.Customer;
import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test9 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = new Customer();customer.setName("李四");Orders orders1 = new Orders();orders1.setName("订单4");orders1.setCustomer(customer);Orders orders2 = new Orders();orders2.setName("订单44");orders2.setCustomer(customer);session.save(customer);session.save(orders1);session.save(orders2);session.beginTransaction().commit();session.close();}
}

3条SQL执行语句。

当添加Customer维护后，（此时Customer和Orders双方都在维护）

package com.htl.test;import com.htl.entity.Customer;
import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;import java.util.HashSet;
import java.util.Set;public class Test9 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = new Customer();customer.setName("王5");Orders orders1 = new Orders();orders1.setName("5");orders1.setCustomer(customer);Orders orders2 = new Orders();orders2.setName("55");orders2.setCustomer(customer);//添加Customer维护Set<Orders> orders = new HashSet<Orders>();orders.add(orders1);orders.add(orders2);customer.setOrders(orders);session.save(customer);session.save(orders1);session.save(orders2);session.beginTransaction().commit();session.close();}
}

5条SQL执行语句。

因为 Customer 和 Orders 都在维护一对多关系，所以会重复设置主外键约束关系。

如何避免这种情况？
1、在 Java 代码中去掉一方维护关系代码。
2、通过配置来解决。

Customer.hbm.xml

<set name="orders" table="orders" lazy="true" inverse="true"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many>
</set>

将 inverse 置为 true，表示 Customer 放弃维护。

再运行：

package com.htl.test;import com.htl.entity.Customer;
import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;import java.util.HashSet;
import java.util.Set;public class Test9 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();Customer customer = new Customer();customer.setName("王5");Orders orders1 = new Orders();orders1.setName("5");orders1.setCustomer(customer);Orders orders2 = new Orders();orders2.setName("55");orders2.setCustomer(customer);//添加Customer维护Set<Orders> orders = new HashSet<Orders>();orders.add(orders1);orders.add(orders2);customer.setOrders(orders);session.save(customer);session.save(orders1);session.save(orders2);session.beginTransaction().commit();session.close();}
}

3条SQL执行语句。

2、cascade

用来设置级联操作。

正常删除有外键约束的表里面的数据时，会报错。

package com.htl.test;import com.htl.entity.Customer;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test10 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//删除Customer customer = session.get(Customer.class,7);session.delete(customer);session.beginTransaction().commit();session.close();}
}

想要删除有外键约束的表里面的数据的方法如下，

方法一：

package com.htl.test;import com.htl.entity.Customer;
import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;import java.util.Iterator;public class Test10 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//删除Customer customer = session.get(Customer.class,7);Iterator<Orders> iterator = customer.getOrders().iterator();while (iterator.hasNext()){session.delete(iterator.next());}session.delete(customer);session.beginTransaction().commit();session.close();}
}

方法二：

实体关系映射⽂件中设置 cascade 值完成级联删除。

Customer.hbm.xml

<set name="orders" table="orders" lazy="true" inverse="true" cascade="delete"><key column="cid"></key><one-to-many class="com.htl.entity.Orders"></one-to-many>
</set>

然后不需要再迭代，直接就能删除了。

package com.htl.test;import com.htl.entity.Customer;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;public class Test10 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//删除Customer customer = session.get(Customer.class,7);session.delete(customer);session.beginTransaction().commit();session.close();}
}

八、Hibernate HQL

HQL：Hibernate Query Language，是 Hibernate 框架提供的一种查询机制，它和 SQL 类似，不同的是 HQL 是面向对象的查询语句，让开发者能够以面向对象的思想来编写查询语句，对 Java 编程是一种很友好的方式。

HQL 不能直接参与数据库的交互，它是中间层语⾔。

Java —》HQL —〉Hibernate —》SQL —〉DB

HQL 只能完成查询、修改、删除，新增是无法操作的。

1、查询对象

查询表中所有数据，自动完成对象的封装，返回 List 集合。

HQL 进行查询，from 关键字后面不能写表名，必须写表对应的实体类名。

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test11 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//查询对象String hql = "from People ";/* 写的是所查询表对应的实体类的名字！尽量写实体类的全类名。也就是 from com.htl.entity.People */Query query = session.createQuery(hql);List<People> list = query.list();for (People people:list){System.out.println(people);}session.close();}
}

注意：People.hbm.xml 里面的 where=“id = 6” 要去掉。这样才能查询出完整的 People 表里面的数据。

2、分页查询

HQL 分页查询可以通过调用 query 的方法来完成。

1、setFirstResult() 设置起始下标

2、setMaxResults() 设置截取长度

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test12 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//分页查询String hql = "from com.htl.entity.People";Query query = session.createQuery(hql);query.setFirstResult(1);query.setMaxResults(3);/* 截取People表里面第2个到第4个的数据。*/List<People> list = query.list();for (People people:list){System.out.println(people);}session.close();}
}

3、where 条件查询

HQL 直接追加 where 关键字作为查询条件，与 SQL 没有区别。

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;public class Test13 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//where条件查询String hql = "from People where id = 6";Query query = session.createQuery(hql);People people = (People) query.list().get(0);System.out.println(people);session.close();}
}

query.list() 返回一个集合，此时集合中只有一个对象，通过下标 0 取出该对象。

当表里面没有符合where查询条件的数据时，query调用uniqueResult()方法时,就不会抛出异常，而是返回null 。

String hql = "from People where id = 0";
Query query = session.createQuery(hql);
People people = (People) query.uniqueResult();
System.out.println(people);

4、模糊查询

查询名称包含“三”的所有记录。

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test14 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//模糊查询String hql = "from People where name like '%三%'";Query query = session.createQuery(hql);List<People> list = query.list();for (People people:list){System.out.println(people);}session.close();}
}

5、order by

按照 id 进行排序。

asc 是生序排列，desc 是降序排列。

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test15 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();String hql = "from People order by id";/* 默认是 asc 升序。*/Query query = session.createQuery(hql);List<People> list = query.list();for (People people:list){System.out.println(people);}session.close();}
}

降序：

String hql = "from People order by id desc ";

6、查询实体对象的属性

package com.htl.test;import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;public class Test16 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//查询实体对象的属性String hql = "select name from People where id = 6";Query query = session.createQuery(hql);String name = (String) query.uniqueResult();System.out.println(name);session.close();}
}

7、占位符

package com.htl.test;import com.htl.entity.People;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test17 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//占位符String hql = "from People where name = :name";Query query = session.createQuery(hql);query.setString("name","张三0");List<People> list = query.list();for (People people:list){System.out.println(people);}session.close();}
}

8、级联查询

package com.htl.test;import com.htl.entity.Customer;
import com.htl.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;import java.util.List;public class Test18 {public static void main(String[] args) {//创建 ConfigurationConfiguration configuration = new Configuration().configure();//获取 SessionFactorySessionFactory sessionFactory = configuration.buildSessionFactory();//获取 SessionSession session = sessionFactory.openSession();//级联查询String hql = "from Customer where name = :name";Query query1 = session.createQuery(hql);query1.setString("name","李四");Customer customer = (Customer) query1.uniqueResult();String hql2 = "from Orders where customer = :customer";Query query2 = session.createQuery(hql2);query2.setEntity("customer",customer);List<Orders> list = query2.list();for (Orders orders:list){System.out.println(orders);}session.close();}
}