JPA笔记1 ManyToOne

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-1" transaction-type="RESOURCE_LOCAL">
 
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
 
        <!-- <class>helloworld.Customer</class> -->
        <properties>
 
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url"
                value="jdbc:mysql://x.x.x.x:3306/jpa-test?useUnicode=true&amp;characterEncoding=utf8" />
            <property name="javax.persistence.jdbc.user" value="admin" />
            <property name="javax.persistence.jdbc.password" value="123456" />
 
            <property name="hibernate.format_sql" value="true" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="update" />
        </properties>
    </persistence-unit>
</persistence>

ManyToOne测试代码

package helloworld;
 
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
 
public class Main {
 
    public static void main(String[] args) {
        // TODO Auto-generated method stub
 
        String persistenceUnitName = "jpa-1";
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(persistenceUnitName);
 
        EntityManager entityManager = entityManagerFactory.createEntityManager();
 
        EntityTransaction transaction = entityManager.getTransaction();
        transaction.begin();
 
        // insert(entityManager);
        // find(entityManager);
        // getReference(entityManager);
        // remove(entityManager);
        // merge(entityManager);
        // flush(entityManager);
        // manyToOnePersist(entityManager);
        // manyToOneFind(entityManager);
        // manyToOneRemove(entityManager);
        manyToOneUpdate(entityManager);
 
        transaction.commit();
        entityManager.close();
        entityManagerFactory.close();
    }
 
    // 1.插入
    private static void insert(EntityManager entityManager) {
        Customer customer = new Customer();
        customer.setEmail("fs2@ss.com");
        customer.setLastName("123");
        customer.setAge(23);
        customer.setCla(33);
        customer.setFf("aa");
        customer.setId(10);
        entityManager.persist(customer);
    }
 
    // 2.查询(注意，如果修改了对象属性，会被提交到数据库)
    private static void find(EntityManager entityManager) {
        Customer customer = entityManager.find(Customer.class, 1);
        System.out.println("----------------");
        System.out.println(customer);
    }
 
    // 3.引用查询，在调用对象的时候才执行sql
    private static void getReference(EntityManager entityManager) {
        Customer customer = entityManager.getReference(Customer.class, 1);
        System.out.println("----------------");
        System.out.println(customer);
    }
 
    // 4.删除
    private static void remove(EntityManager entityManager) {
        Customer customer = entityManager.find(Customer.class, 2);
        entityManager.remove(customer);
        System.out.println("----------------");
    }
 
    // 5.合并(根据ID判断，存在ID的记录并且数据有变化的则update，不存在则insert)
    private static void merge(EntityManager entityManager) {
        Customer customer = new Customer();
        customer.setEmail("5@ss.com");
        customer.setLastName("4");
        customer.setAge(2);
        customer.setCla(2);
        customer.setFf("3");
 
        Customer customer2 = entityManager.merge(customer);// 没有id，插入数据
 
        System.out.println("----------------" + customer.getId());
        System.out.println("----------------" + customer2.getId());
        System.out.println(customer.equals(customer2));
 
        Customer customer_1 = new Customer();
        customer_1.setEmail("5@ss.com");
        customer_1.setLastName("4");
        customer_1.setAge(21);
        customer_1.setCla(2);
        customer_1.setFf("3");
        customer_1.setId(5);
 
        Customer customer_2 = entityManager.merge(customer_1);// 有id的数据，如果数据有变化则修改
 
        System.out.println("----------------" + customer_1.getId());
        System.out.println("----------------" + customer_2.getId());
        System.out.println(customer_1.equals(customer_2));
    }
 
    // 6.将缓存数据刷新到数据库，不执行该方法，需要在执行commit的时候才提交到数据库
    private static void flush(EntityManager entityManager) {
        Customer customer = entityManager.find(Customer.class, 1);
        System.out.println("----------------");
        customer.setAge(1234);
        entityManager.flush();
        System.out.println(customer);
    }
 
    // 7.保存多对一的数据时，建议先保存一的，再保存多的，这样不会多出update语句
    private static void manyToOnePersist(EntityManager entityManager) {
 
        Order order = new Order();
        order.setOrderName("order1");
 
        Order order2 = new Order();
        order2.setOrderName("order2");
 
        Customer customer = new Customer();
        customer.setEmail("5@ss.com");
        customer.setLastName("4");
        customer.setAge(2);
        customer.setCla(2);
        customer.setFf("3");
 
        order.setCustomer(customer);
        order2.setCustomer(customer);
 
        entityManager.persist(customer);
        entityManager.persist(order);
        entityManager.persist(order2);
 
    }
 
    // 8.查询多对一数据
    private static void manyToOneFind(EntityManager entityManager) {
        Order order = entityManager.find(Order.class, 1);
        System.out.println(order.getOrderName());
        System.out.println(order.getCustomer());
        order.setOrderName("victor");
    }
 
    // 9.不能直接删除一的一端，因为有外键关联
    private static void manyToOneRemove(EntityManager entityManager) {
        Customer customer = entityManager.find(Customer.class, 12);
        entityManager.remove(customer);
    }
 
    // 10.修改多对一数据
    private static void manyToOneUpdate(EntityManager entityManager) {
        Order order = entityManager.find(Order.class, 3);
        order.setOrderName("vv");
 
        order.getCustomer().setAge(100);
    }
}

Customer类：

package helloworld;
 
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
 
@Table(name = "JPA_CUSTOMERS")
@Entity
public class Customer {
 
    @Override
    public String toString() {
        return "Customer [id=" + id + ", lastName=" + lastName + ", email=" + email + ", age=" + age + ", cla=" + cla + ", ff=" + ff + "]";
    }
 
    private Integer id;
    private String lastName;
    private String email;
    private int age;
    private int cla;
    private String ff;
 
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Id
    public Integer getId() {
        return id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    public String getLastName() {
        return lastName;
    }
 
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
 
    public String getEmail() {
        return email;
    }
 
    public void setEmail(String email) {
        this.email = email;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public int getCla() {
        return cla;
    }
 
    public void setCla(int cla) {
        this.cla = cla;
    }
 
    public String getFf() {
        return ff;
    }
 
    public void setFf(String ff) {
        this.ff = ff;
    }
 
}

Order类：

package helloworld;
 
import javax.persistence.Column;
import javax.persistence.ConstraintMode;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.ForeignKey;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
 
@Table(name = "JPA_ORDER")
@Entity
public class Order {
 
    private Integer id;
    private String orderName;
 
    private Customer customer;
 
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Id
    public Integer getId() {
        return id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    @Column(name = "order_name")
    public String getOrderName() {
        return orderName;
    }
 
    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }
 
    //映射单向n-1的关联关系
    @JoinColumn(name = "customer_id")//, foreignKey = @ForeignKey(ConstraintMode.NO_CONSTRAINT))
    @ManyToOne(fetch=FetchType.LAZY)
    public Customer getCustomer() {
        return customer;
    }
 
    public void setCustomer(Customer customer) {
        this.customer = customer;
    }
 
    @Override
    public String toString() {
        return "Order [id=" + id + ", orderName=" + orderName + ", customer=" + customer + "]";
    }
 
}