Question

那是我的Users.java

package com.serwis.model;


import javax.persistence.*;

import java.util.Arrays;
import java.util.Set;


@Entity
@Table(name="Users")
public class Users {

    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    @Column(name="id")
    private int id;

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

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

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

    @Column(name="avatar")
    private byte[] avatar;

    @OneToMany(mappedBy="users", cascade = CascadeType.ALL,fetch = FetchType.EAGER)
    private Set<Post> posts;

    public Users(){}

    public Users(int id, String login, String password, String email, byte[] avatar) {
        this.id = id;
        this.login = login;
        this.password = password;
        this.email = email;
        this.avatar = avatar;
    }


    public Users(byte[] avatar, String email, String password, String login) {
        this.avatar = avatar;
        this.email = email;
        this.password = password;
        this.login = login;
    }

    @Override
    public String toString() {
        return "Users{" +
                "id=" + id +
                ", login='" + login + '\'' +
                ", password='" + password + '\'' +
                ", email='" + email + '\'' +
                ", avatar="  +
                ", posts="  + posts.size()+
                '}';
    }

    public int getId() {
        return id;
    }

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

    public String getLogin() {
        return login;
    }

    public void setLogin(String login) {
        this.login = login;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public byte[] getAvatar() {
        return avatar;
    }

    public void setAvatar(byte[] avatar) {
        this.avatar = avatar;
    }


}

Post.java

import javax.persistence.*;
import java.util.Date;


@Entity
@Table(name="Post")
public class Post {

    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    @Column(name="id")
    private int id;


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

    @Column(name="date")
    private Date date;

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

    @ManyToOne
    @JoinColumn(name="id")
    private Users users;

    public Post(){}

    public Post( String content, Date date, String tags) {
        this.content = content;
        this.date = date;
        this.tags = tags;
    }

    public Post(String content, Date date, String tags, Users users) {
        this.content = content;
        this.date = date;
        this.tags = tags;
        this.users = users;
    }

    @Override
    public String toString() {
        return "Post{" +
                "id=" + id +
                ", content='" + content + '\'' +
                ", date=" + date +
                ", tags='" + tags + '\'' +
                ", users=" + users +
                '}';
    }

    public int getId() {
        return id;
    }

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

    public Users getUsers() { return users; }

    public void setUsers(Users users) { this.users = users; }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public String getTags() {
        return tags;
    }

    public void setTags(String tags) {
        this.tags = tags;
    }
}

Test.java 包com.serwis;

import com.serwis.model.Chat;
import com.serwis.model.Photo;
import com.serwis.model.Post;
import com.serwis.model.Users;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

import java.util.List;


/**
 * Created by Jodanpotasu on 2016-07-17.
 */
public class TEST {

    public static void main(String[] args){
        Configuration configuration = new Configuration().configure().addAnnotatedClass(Users.class).addAnnotatedClass(Post.class);
        ServiceRegistry serviceRegistry
                = new StandardServiceRegistryBuilder()
                .applySettings(configuration.getProperties()).build();

        // builds a session factory from the service registry
        SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);



        try{
            Users user = new Users(null,"YYYYYYYYYYYYY","dupa","dupa");
            Post post = new Post("content",null,"tags",user);

            Session session = sessionFactory.openSession();
            session.beginTransaction();
            session.save(user);
            session.save(post);

            Query query = session.createQuery("from Users");
            List list = query.list();

            Query query1 = session.createQuery("from Post");
            List list1 = query1.list();

            session.getTransaction().commit();


            session.close();

            System.out.println(list);

            System.out.println("post");
            System.out.println(list1);

        }catch (Exception e){
            System.out.println("blad\n\n");
            System.out.println(e);
        } finally {
            System.out.println("zrobiono");
        }





    }
}

的hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <!-- JDBC connection settings -->
        <property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property>
        <property name="connection.url">jdbc:hsqldb:file:database/serwisDB;hsqldb.write_delay=false;shutdown=true;</property> <!--shutdown=true; -->
        <property name="connection.username">sa</property>
        <property name="connection.password"></property>
        <!--https://www.progress.com/jdbc/resources/tutorials/connection-pooling/connection -->
        <property name="connection.pool_size">1</property>

        <!-- SQL DIALECT -->
        <property name="hibernate.dialect">org.hibernate.dialect.HSQLDialect</property>

        <!-- SHOW SQL OUTPUT -->
        <property name="show_sql">true</property>

        <property name="hibernate.current_session_context_class">thread</property>

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



    </session-factory>
</hibernate-configuration>

从控制台输出

java.lang.NullPointerException
zrobiono
22:40:25.391 [pool-1-thread-1] DEBUG org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl - Connection pool now considered primed; min-size will be maintained

Process finished with exit code -1

我的问题是，我不明白为什么它在我有一些错误的地方不起作用。我正在尝试更改设置为列表，稍后更改FetchType.EAGER等但没有任何效果。

结构：＆。1，许多＆GT; - 用户，帖子

我没有看到任何关于最新hibernate的好教程:(

Answer 1

您的Users类需要对Post集合进行一些公共访问，您必须将Post对象添加到集合中，并将其设置为User对象。看起来应该是这样的。

        Users user = new Users(null,"YYYYYYYYYYYYY","dupa","dupa");
        Post post = new Post("content",null,"tags",user);
        user.getPosts().add(post);

Answer 2

您的以下方法用户类抛出错误：

@Override public String toString() { return "Users{" + "id=" + id + ", login='" + login + '\'' + ", password='" + password + '\'' + ", email='" + email + '\'' + ", avatar=" + ", posts=" + posts.size()+ '}'; }

请为posts.size（）添加空检查。

此外，如果您无法理解为什么会出现错误，请打印出堆栈跟踪/调试错误。

Hibernate - 获取List / Set

2 个答案: