Hibernate每個(gè)層次類一張表（使用注釋）

在上一文章中，我們使用xml文件將繼承層次映射到一個(gè)表。 在這里，我們將使用注釋來執(zhí)行同樣的任務(wù)。需要使用@Inheritance(strategy = InheritanceType.SINGLE_TABLE)，@DiscriminatorColumn和@DiscriminatorValue注釋，以便根據(jù)層次結(jié)構(gòu)策略映射表。

在每個(gè)層次結(jié)構(gòu)一張表的情況下，只需要一個(gè)表來映射繼承層次結(jié)構(gòu)。 這里，在表中創(chuàng)建一個(gè)額外的列(也稱為discriminator列)來標(biāo)識該類。

下面來看看看繼承層次結(jié)構(gòu)：

這個(gè)層次結(jié)構(gòu)中有三個(gè)類。 Employee是Regular_Employee和Contract_Employee類的父類。

此層次結(jié)構(gòu)的表結(jié)構(gòu)如下所示：

使用注釋的每個(gè)層次結(jié)構(gòu)一張表示例

您需要按照以下步驟創(chuàng)建簡單示例：

• 創(chuàng)建持久化類
• 創(chuàng)建配置文件
• 創(chuàng)建類來存儲提取數(shù)據(jù)

創(chuàng)建一個(gè)項(xiàng)目名稱為：，其結(jié)構(gòu)如下圖所示 -

1)創(chuàng)建持久類

您需要?jiǎng)?chuàng)建表示繼承的持久化類。為上面的層次結(jié)構(gòu)創(chuàng)建三個(gè)類：

文件：Employee.java

package com.yiibai;

import javax.persistence.*;

@Entity  
@Table(name = "employee101")  
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)  
@DiscriminatorColumn(name="type",discriminatorType=DiscriminatorType.STRING)  
@DiscriminatorValue(value="employee")  
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @Column(name = "name")
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    // setters and getters
}

文件：Regular_Employee.java

package com.yiibai;

/**
 * 
 * @author by maxsu
 * @copyright http://www.yiibai.com
 * @link download at: http://www.yiibai.com/siteinfo/download.html
 */
import javax.persistence.*;

@Entity  
@DiscriminatorValue("regularemployee")  
public class Regular_Employee extends Employee {

    @Column(name = "salary")
    private float salary;

    @Column(name = "bonus")
    private int bonus;

    public float getSalary() {
        return salary;
    }

    public void setSalary(float salary) {
        this.salary = salary;
    }

    public int getBonus() {
        return bonus;
    }

    public void setBonus(int bonus) {
        this.bonus = bonus;
    }

}

文件：Contract_Employee.java

package com.yiibai;

/**
 * 
 * @author by maxsu
 * @copyright http://www.yiibai.com
 * @link download at: http://www.yiibai.com/siteinfo/download.html
 */
import javax.persistence.*;

@Entity  
@DiscriminatorValue("contractemployee")  
public class Contract_Employee extends Employee {

    @Column(name = "pay_per_hour")
    private float pay_per_hour;

    @Column(name = "contract_duration")
    private String contract_duration;

    public float getPay_per_hour() {
        return pay_per_hour;
    }

    public void setPay_per_hour(float payPerHour) {
        pay_per_hour = payPerHour;
    }

    public String getContract_duration() {
        return contract_duration;
    }

    public void setContract_duration(String contractDuration) {
        contract_duration = contractDuration;
    }
}

2)在配置文件中添加持久化類

打開hibernate.cfg.xml文件，并添加實(shí)體類的項(xiàng)，如下所示：

<?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">

<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>

    <session-factory>
         <property name="hbm2ddl.auto">update</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/test</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123456</property>
        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>

        <property name="show_sql">true</property>
        <mapping class="com.yiibai.Employee"/>  
        <mapping class="com.yiibai.Contract_Employee"/>   
        <mapping class="com.yiibai.Regular_Employee"/>   
    </session-factory>

</hibernate-configuration>

hbm2ddl.auto屬性定義是用于在數(shù)據(jù)庫中自動(dòng)創(chuàng)建表。

3)創(chuàng)建存儲持久對象的類

在這個(gè)類中，我們只是將 Employee 對象存儲在數(shù)據(jù)庫中。
文件：MainTest.java

package com.yiibai;

import org.hibernate.*;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

/**
 * 
 * @author by maxsu
 * @copyright http://www.yiibai.com
 * @link download at: http://www.yiibai.com/siteinfo/download.html
 */

public class MainTest {
    public static void main(String[] args) {
        // 但在5.1.0版本匯總，hibernate則采用如下新方式獲?。?        // 1. 配置類型安全的準(zhǔn)服務(wù)注冊類，這是當(dāng)前應(yīng)用的單例對象，不作修改，所以聲明為final
        // 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，默認(rèn)在類路徑下尋找名為hibernate.cfg.xml的文件
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure("hibernate.cfg.xml").build();
        // 2. 根據(jù)服務(wù)注冊類創(chuàng)建一個(gè)元數(shù)據(jù)資源集，同時(shí)構(gòu)建元數(shù)據(jù)并生成應(yīng)用一般唯一的的session工廠
        SessionFactory sessionFactory = new MetadataSources(registry)
                .buildMetadata().buildSessionFactory();

        /**** 上面是配置準(zhǔn)備，下面開始我們的數(shù)據(jù)庫操作 ******/
        Session session = sessionFactory.openSession();// 從會(huì)話工廠獲取一個(gè)session

        // creating transaction object
        Transaction t = session.beginTransaction();

        Employee e1 = new Employee();
        e1.setName("用戶名-01");

        Regular_Employee e2 = new Regular_Employee();
        e2.setName("yiibai su");
        e2.setSalary(50002);
        e2.setBonus(5);

        Contract_Employee e3 = new Contract_Employee();
        e3.setName("Mina su");
        e3.setPay_per_hour(1010);
        e3.setContract_duration("15 hours");

        session.persist(e1);
        session.persist(e2);
        session.persist(e3);

        t.commit();
        session.close();
        System.out.println("success");
    }
}

執(zhí)行上面示例，輸出結(jié)果如下 -

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Sun Mar 26 02:19:13 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Sun Mar 26 02:19:14 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Hibernate: select next_val as id_val from hibernate_sequence for update
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence for update
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence for update
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: insert into employee101 (name, type, id) values (?, 'employee', ?)
Hibernate: insert into employee101 (name, bonus, salary, type, id) values (?, ?, ?, 'regularemployee', ?)
Hibernate: insert into employee101 (name, contract_duration, pay_per_hour, type, id) values (?, ?, ?, 'contractemployee', ?)
success

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