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JPA（七）：映射关联关系------映射双向多对一的关联关系

映射双向多对一的关联关系

修改Customer.java

package com.dx.jpa.singlemanytoone;

import java.util.Date;

import java.util.HashSet;

import java.util.Set;

import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.OneToMany;

import javax.persistence.Table;

import javax.persistence.Temporal;

import javax.persistence.TemporalType;

import javax.persistence.Transient;

@Entity

@Table(name = "jpa_customer")

public class Customer {

    private Integer id;

    private String fullName;

    private Integer age;

    private Date birth;

    private Date createDate;

    private Set<Order> orders = new HashSet<>();

    @Id

    @GeneratedValue(strategy = GenerationType.AUTO)

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    @Column(name = "FULL_NAME", length = 64, nullable = false)

    public String getFullName() {

        return fullName;

    }

    public void setFullName(String fullName) {

        this.fullName = fullName;

    }

    public Integer getAge() {

        return age;

    }

    public void setAge(Integer age) {

        this.age = age;

    }

    @Temporal(TemporalType.DATE)

    public Date getBirth() {

        return birth;

    }

    public void setBirth(Date birth) {

        this.birth = birth;

    }

    @Temporal(TemporalType.TIMESTAMP)

    public Date getCreateDate() {

        return createDate;

    }

    public void setCreateDate(Date createDate) {

        this.createDate = createDate;

    }

    // 映射一对多的关联关系

    // @JoinColumn 用来映射一对多的关联关系

    // @OneToMany 用来映射外键列

    @JoinColumn(name = "CUSTOMER_ID")

    @OneToMany(fetch=FetchType.EAGER,cascade=CascadeType.REMOVE)

    public Set<Order> getOrders() {

        return orders;

    }

    public void setOrders(Set<Order> orders) {

        this.orders = orders;

    }

    // 帮助方法，不希望保存到数据库，但是需要动态获取Customer对象的属性。

    @Transient

    public String getCustomerInfo() {

        return "username:" + fullName + ",age:" + age;

    }

}

修改Order.java

package com.dx.jpa.singlemanytoone;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

@Entity

@Table(name = "jpa_order")

public class Order {

    private Integer id;

    private String name;

    private Customer Customer;

    @Id

    @GeneratedValue(strategy = GenerationType.AUTO)

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @JoinColumn(name = "CUSTOMER_ID")

    @ManyToOne(fetch = FetchType.LAZY)

    public Customer getCustomer() {

        return Customer;

    }

    public void setCustomer(Customer customer) {

        Customer = customer;

    }

}

修改persistence.xml

<?xml version="1.0" encoding="UTF-8"?>

<persistence version="2.0"

    xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

    <persistence-unit name="Jpa-helloword"

        transaction-type="RESOURCE_LOCAL">

        <!-- 配置使用什么 ORM 产品来作为 JPA 的实现 -->

        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

        <!-- 添加持久化类 -->

        <class>com.dx.jpa.singlemanytoone.Customer</class>

        <class>com.dx.jpa.singlemanytoone.Order</class>

        <properties>

            <!-- 数据库的相关配置 -->

            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />

            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://127.0.0.1:3306/jpa" />

            <property name="javax.persistence.jdbc.user" value="root" />

            <property name="javax.persistence.jdbc.password" value="root" />

            <!-- 指定方言

            MySQL                org.hibernate.dialect.MySQLDialect

            MySQL with InnoDB    org.hibernate.dialect.MySQLInnoDBDialect

            MySQL with MyISAM    org.hibernate.dialect.MySQLMyISAMDialect

            MySQL5                org.hibernate.dialect.MySQL5Dialect

            MySQL5 with InnoDB    org.hibernate.dialect.MySQL5InnoDBDialect

            -->

            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />

            <property name="hibernate.show_sql" value="true" />

            <property name="hibernate.format_sql" value="true" />

            <!--

            create：每次加载hibernate时都会删除上一次的生成的表，然后根据你的model类再重新来生成新表，哪怕两次没有任何改变也要这样执行，这就是导致数据库表数据丢失的一个重要原因。<br>

            create-drop ：每次加载hibernate时根据model类生成表，但是sessionFactory一关闭,表就自动删除。<br>

            update：最常用的属性，第一次加载hibernate时根据model类会自动建立起表的结构（前提是先建立好数据库），以后加载hibernate时根据 model类自动更新表结构，即使表结构改变了但表中的行仍然存在不会删除以前的行。要注意的是当部署到服务器后，表结构是不会被马上建立起来的，是要等 应用第一次运行起来后才会。<br>

            validate ：每次加载hibernate时，验证创建数据库表结构，只会和数据库中的表进行比较，不会创建新表，但是会插入新值。 <br>

            -->

            <property name="hibernate.hbm2ddl.auto" value="update" />

        </properties>

    </persistence-unit>

</persistence>

特别注意：配置双向多对一的关联关系时，Customer.java配置：

    // 映射一对多的关联关系

    // @JoinColumn 用来映射一对多的关联关系

    // @OneToMany 用来映射外键列

    @JoinColumn(name = "CUSTOMER_ID")

    @OneToMany(fetch=FetchType.EAGER,cascade=CascadeType.REMOVE)

    public Set<Order> getOrders() {

        return orders;

    }

Order.java配置：

    @JoinColumn(name = "CUSTOMER_ID")

    @ManyToOne(fetch = FetchType.LAZY)

    public Customer getCustomer() {

        return Customer;

    }

表关联关系：

JPA（七）：映射关联关系------映射双向多对一的关联关系-LMLPHP

测试添加：

添加测试函数：

    @Test

    public void testPersist() {

        Customer customer = new Customer();

        customer.setFullName("AA");

        customer.setAge(26);

        customer.setBirth(new Date());

        customer.setCreateDate(new Date());

        Order order1 = new Order();

        order1.setName("O-AA-01");

        Order order2 = new Order();

        order2.setName("O-AA-02");

        customer.getOrders().add(order1);

        customer.getOrders().add(order2);

        order1.setCustomer(customer);

        order2.setCustomer(customer);

        entityManager.persist(customer);

        entityManager.persist(order1);

        entityManager.persist(order2);

    }

执行sql::

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

        jpa_customer

        (age, birth, createDate, FULL_NAME, id)

    values

        (?, ?, ?, ?, ?)

Hibernate:

    insert

    into

        jpa_order

        (CUSTOMER_ID, name, id)

    values

        (?, ?, ?)

Hibernate:

    insert

    into

        jpa_order

        (CUSTOMER_ID, name, id)

    values

        (?, ?, ?)

Hibernate:

    update

        jpa_order

    set

        CUSTOMER_ID=?

    where

        id=?

Hibernate:

    update

        jpa_order

    set

        CUSTOMER_ID=?

    where

        id=?

测试查询：

测试查询函数：

    @Test

    public void testFind() {

        Customer customer = entityManager.find(Customer.class, 1);

        System.out.println(customer.getFullName());

        System.out.println(customer.getOrders().size());

    }

执行sql语句：

Hibernate:

    select

        customer0_.id as id1_0_0_,

        customer0_.age as age2_0_0_,

        customer0_.birth as birth3_0_0_,

        customer0_.createDate as createDa4_0_0_,

        customer0_.FULL_NAME as FULL_NAM5_0_0_,

        orders1_.CUSTOMER_ID as CUSTOMER3_1_1_,

        orders1_.id as id1_1_1_,

        orders1_.id as id1_1_2_,

        orders1_.CUSTOMER_ID as CUSTOMER3_1_2_,

        orders1_.name as name2_1_2_

    from

        jpa_customer customer0_

    left outer join

        jpa_order orders1_

            on customer0_.id=orders1_.CUSTOMER_ID

    where

        customer0_.id=?

BB

2

测试修改：

测试修改函数：

执行sql语句：

测试删除：

4）映射双向一对一的关联关系

5）映射双向多对多的关联关系

05-11 20:01
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