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所以我有两个简单的豆子——FatKid 和汉堡包。现在，由于我不知道的原因，我不仅需要查找某人吃的所有汉堡包，还需要查找谁吃了哪个特定的汉堡包。上代码！

FatKid.java

import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Table
@Entity
public class FatKid {

    private int id;
    private String name;
    private List<Hamburger> hamburgers;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "FATKID_ID")
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

    @Column
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name="HAMBURGER_ID")
    public List<Hamburger> getHamburgers() {
        return hamburgers;
    }
    public void setHamburgers(List<Hamburger> hamburgers) {
        this.hamburgers = hamburgers;
    }

}

汉堡包.java

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
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
@Entity
public class Hamburger {

    private int id;
    private String description;
    private FatKid whoDoneAteMe;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "HAMBURGER_ID")
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

    @Column
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="FATKID_ID")
    public FatKid getWhoDoneAteMe() {
        return whoDoneAteMe;
    }
    public void setWhoDoneAteMe(FatKid whoDoneAteMe) {
        this.whoDoneAteMe = whoDoneAteMe;
    }

}

休眠.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>
        <property name="hibernate.connection.driver_class">org.h2.Driver</property>
        <property name="hibernate.connection.url">jdbc:h2:~/routesetting</property>
        <property name="hibernate.dialect">org.hibernate.dialect.H2Dialect</property>

        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>

        <!-- Drop and re-create the database schema on startup -->
        <property name="hbm2ddl.auto">create-drop</property>

        <mapping class="FatKid" />
        <mapping class="Hamburger" />

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

依赖关系

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>3.6.7.Final</version>
</dependency>

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.3.160</version>
</dependency>

<dependency>
    <groupId>javassist</groupId>
    <artifactId>javassist</artifactId>
    <version>3.9.0.GA</version>
</dependency>

客户

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class OmNom {

    private static final SessionFactory sessionFactory = buildSessionFactory();

    public static void main(String[] args) {

        Session session = sessionFactory.openSession();

        session.beginTransaction();
        FatKid fk = new FatKid();
        fk.setName("Darrell");
        session.save(fk);
        session.getTransaction().commit();

        session.beginTransaction();
        Hamburger hamburger_1 = new Hamburger();
        hamburger_1.setDescription("Juicy quarter pounder with cheese");
        hamburger_1.setWhoDoneAteMe(fk);
        session.save(hamburger_1);
        session.getTransaction().commit();

        session.beginTransaction();
        Hamburger hamburger_2 = new Hamburger();
        hamburger_2.setDescription("Ground buffalo burger topped with bacon and a sunny-side egg");
        hamburger_2.setWhoDoneAteMe(fk);
        session.save(hamburger_2);
        session.getTransaction().commit();

        sessionFactory.close();

    }

    private static SessionFactory buildSessionFactory() {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            return new Configuration().configure().buildSessionFactory();
        }
        catch (Throwable ex) {
            // Make sure you log the exception, as it might be swallowed
            throw new ExceptionInInitializerError(ex);
        }
    }

}

所以当我运行代码时，我最终得到了输出（和截断的堆栈跟踪）

Hibernate: insert into FatKid (FATKID_ID, name) values (null, ?)
Hibernate: insert into Hamburger (HAMBURGER_ID, description, FATKID_ID) values (null, ?, ?)
Hibernate: insert into Hamburger (HAMBURGER_ID, description, FATKID_ID) values (null, ?, ?)
Exception in thread "main" org.hibernate.exception.ConstraintViolationException: could not insert: [Hamburger]
        ...
Caused by: org.h2.jdbc.JdbcSQLException: Referential integrity constraint violation: "FK43797FE95067143: PUBLIC.HAMBURGER FOREIGN KEY(HAMBURGER_ID) REFERENCES PUBLIC.FATKID(FATKID_ID)"; SQL statement:
insert into Hamburger (HAMBURGER_ID, description, FATKID_ID) values (null, ?, ?) [23506-160]
        ...

所以第一个汉堡包被保存了，但它在第二个汉堡包上爆炸了。两者都应该能够使用 FatKid 的 id 作为他们的外键，但它似乎不起作用。任何见解将不胜感激。

谢谢，凯文

4

1 回答 1

13

你的映射对我来说看起来很奇怪。您在关系的两边都有一个@JoinColumn，每个都指向另一个表的主键。这似乎不是 OneToMany 关系。

您的 OneToMany 应该告诉关系的所有者：

@OneToMany(cascade = CascadeType.ALL, mappedBy = "whoDoneAteMe")
public List<Hamburger> getHamburgers() {
    return hamburgers;
}

然后在另一边：

@ManyToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "fatkid_id")
public FatKid getWhoDoneAteMe() {
    return whoDoneAteMe;
}

您也可以进一步优化您的代码。由于您的 FatKid 对象知道 Hamburger 对象并且您已经配置了级联，您可以这样做：

    session.beginTransaction();
    FatKid fk = new FatKid();
    fk.setName("Darrell");

    Hamburger hamburger_1 = new Hamburger();
    hamburger_1.setDescription("Juicy quarter pounder with cheese");
    hamburger_1.setWhoDoneAteMe(fk);
    fk.getHamburgers().add(hamburger1);

    Hamburger hamburger_2 = new Hamburger();
    hamburger_2.setDescription("Ground buffalo burger topped with bacon and a sunny-side egg");
    hamburger_2.setWhoDoneAteMe(fk);
    fk.getHamburgers().add(hamburger2);

    session.save(fk);
    session.getTransaction().commit();

    sessionFactory.close();

上面的代码应该只用一个提交操作和一个事务来保存完整的对象图。

于 2011-10-23T22:04:57.147 回答