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 + "]";

    }

}

巴特西

JPA笔记1 ManyToOne

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