Java Hibernate oneToOne映射未读取joinColumn类实例

SQL表的输出，即使代码中存在异常

package com.hibernatetest;

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.OneToOne;
import javax.persistence.Table;
import javax.persistence.Transient;

@Entity
@Table(name = "country")
public class Country {

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

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


@Transient
private int rank;

@ManyToOne
@JoinColumn(name="fk_cont_id")
private Continent continent;

@OneToOne(mappedBy="country")
private HeadOfState hos;

public HeadOfState getHos() {
    return hos;
}

public void setHos(HeadOfState hos) {
    this.hos = hos;
}

public Continent getContinent() {
    return continent;
}

public Country() {
    ;
}
public Country(String name) {
    this.name = name;
}
public void setContinent(Continent continent) {
    this.continent = continent;
}

public Integer getId() {
    return id;
}

public void setName(String name) {
    this.name = name;
}

public String getName() {
    return name;
}

public void setRank(int rank) {
    this.rank = rank;
}

public int getRank() {
    return rank;
}

public void addCountryToDb(Continent cont) {
    continent = cont;
}

}


package com.hibernatetest;

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.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name="hos")
public class HeadOfState {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="hos_id")
private Integer id;

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

@OneToOne
@JoinColumn(name="fk_ctry_id")
private Country country;

public HeadOfState() {

}

public HeadOfState(String name) {
    this.name=name;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public Country getCountry() {
    return country;
}

public void setCountry(Country country) {
    this.country = country;
}



}

Session session = HibernateUtil.getSessionFactory().openSession();
    try {
    Transaction transaction = session.getTransaction();
    Country countObj = (Country)session.get(Country.class, 62);
    HeadOfState hos = new HeadOfState("ghanaKing");
    hos.setCountry(countObj);
    transaction.begin();
    session.save(hos);
    transaction.commit();

    Country cont = (Country)session.get(Country.class, 62);
    System.out.println("name of country is "+cont.getName());
    System.out.println("name of continent is "+cont.getContinent().getName());
    HeadOfState newhos = cont.getHos();
    if (newhos == null) {
        throw new Exception("hos obj is null even after storing it");
    }
    System.out.println("Name of HOS is "+cont.getHos().getName());
    } catch (Exception ex) {
        System.out.println("exception has happened: "+ex.getMessage());
        throw ex;
    } finally {
        session.close();
        HibernateUtil.shutdown();
    }
}

Eclipse异常

ysql> select * from hos;
host_id, hos_name, fk_ctry_id
2,       ghanaKing,62
1 row in set (0.00 sec)

mysql> select * from country
ctry_id, ctry_name, fk_cont_id
60, England, 30
62, ghana, 30

---

尝试在关联的两侧设置相关对象。 保存实例时：

name of country is ghana
name of continent is Asia
exception has happened hos obj is null even after storing it

Nov 24, 2014 2:54:29 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH000030: Cleaning up connection pool [jdbc:mysql://172.23.180.81:3306/test]
Exception in thread "main" java.lang.Exception: hos obj is null even after storing it
    at com.hibernatetest.SqlTest.main(SqlTest.java:37)

加

hos.setCountry(countObj);

---

您可以将一个方便的方法添加到任何一个实例中，例如，因此您可以在两个实例中同时调用一个方法。

格式设置非常倾斜。我不熟悉stackoverlow，对如何设置格式感到非常困惑。问题在于，在上面的代码中，我能够准确地存储HeadOfState的值，但在同一代码中，当我尝试获取值时，我得到一个异常，即对象不存在。基本上，我检索country对象，它有HeadOfState对象hos，出于某种原因，它显示为null。即使DB表有recordTry

会话。persist

而不是

会话。save

请注意，在DB中，在hos表中，您有列host_id，在映射类中，您有以下内容：@column（name=“hos_id”）谢谢，但问题出在其他地方（代码与我发布的内容相比没有太大变化）。在具有发生异常的main方法的类中，当我使用main运行该类时，如果在第一次运行时，我执行session.save，并且正如您看到的，当我进一步检索时，我得到了我正在谈论的异常。但是在下一次运行中，如果我只是尝试检索保存的对象，它将非常有效。我想问题是别的

countObj.setHos(hos);