休眠oneToOne映射不读joinColumn类实例

Question

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(); 
    } 
} 

输出的SQL表即使在代码中的异常

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 

Eclipse的例外

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) 

Answer 1

尝试两侧设置相关对象协会。 当您保存您的实例：

hos.setCountry(countObj); 

，并添加

countObj.setHos(hos); 

你可以一个方便易方法添加到您的任何实例一样的，因此，你会打电话两种方法之一INSEAD。