JPA 多对一单向

 

http://ningnian169.blog.51cto.com/2417825/452825

 

 

自己做了一个单向多对一的例子。

     主贴类(1)-----回帖类(m)

     Topic(1)------Feedback(m)

      persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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_1_0.xsd">
    <persistence-unit name="JpaTest" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>com.entity.Topic</class>
    <class>com.entity.Feedback</class>
    <exclude-unlisted-classes>true</exclude-unlisted-classes>
    <properties>
        <property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver"/>
        <property name="hibernate.connection.url" value="jdbc:oracle:thin:@localhost:1521:orcl"/>
        <property name="hibernate.connection.username" value="ningnian"/>
        <property name="hibernate.connection.password" value="ningningx"/>
        <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/>
        <property name="hibernate.show_sql" value="true" />
        <property name="hibernate.hbm2ddl.auto" value="update"/>
    </properties>
    </persistence-unit>
</persistence>

TopicEntity

 

package com.entity;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table
public class Topic implements Serializable {

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    private int id;
    private String author;
    private String title;
    private String context;

    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getId() {
        return id;
    }

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

    @Column(length = 20)
    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    @Column(length = 20)
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @Column(length = 20)
    public String getContext() {
        return context;
    }

    public void setContext(String context) {
        this.context = context;
    }

}

Feedback

 

package com.entity;

import java.io.Serializable;

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.ManyToOne;

@Entity
public class Feedback implements Serializable {

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    private int id;
    private String author;
    private String context;
    private Topic topics;

    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getId() {
        return id;
    }

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

    @Column
    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    @Column
    public String getContext() {
        return context;
    }

    public void setContext(String context) {
        this.context = context;
    }

    /**
     * cascade = CascadeType.MERGE--级联更新 cascade=CascadeType.PERSIST--级联持久
     * cascade=CascadeType.REMOVE--级联删除 cascade=CascadeType.REFRESH--
     * 级联刷新--在业务逻辑中可能对象进行修改，但是读取出来并不是最新的数据。 如果需要最新的数据，这时就得需要级联刷新 fetch =
     * FetchType.LAZY--开启延迟加载。 fetch = FetchType.EAGER--即时加载 optional--boolean
     * 在数据中，这个字段是否为空 optional=false,这个选项不可以空
     */
    @ManyToOne(cascade = CascadeType.REFRESH, fetch = FetchType.LAZY, optional = false)
    /**
     * @JoinColumn(name = "top_id") 指定外键
     */
    @JoinColumn(name = "top_id")
    public Topic getTopics() {
        return topics;
    }

    public void setTopics(Topic topics) {
        this.topics = topics;
    }

}

测试类

 

@Test
    public void testFeedback() {
        EntityManagerFactory factory = Persistence
                .createEntityManagerFactory("JpaTest");
        EntityManager manager = factory.createEntityManager();

        Topic topic = new Topic();
        topic.setTitle("test");
        topic.setContext("this is test");
        topic.setAuthor("ning");

        Feedback fk = new Feedback();
        fk.setAuthor("nian");
        fk.setContext("________");
        fk.setTopics(topic);

        manager.getTransaction().begin();
        manager.persist(fk);
        manager.getTransaction().commit();

    }