为什么我会得到org.hibernate.id.IdentifierGenerationException？

问题描述

运行我的主类 （Runner）程序时，我得到以下异常：

  org.hibernate.id.IdentifierGenerationException：试图从null一对一属性中指定id 
：country 
  
 
 
 
我不知道原因，为什么我得到这个异常。
 
 
 
映射xml： 
 
 
 < hibernate-mapping> 
< class name =pojo.Countrytable =country> 
< id name =countryIDcolumn =c_id> 
< generator class =increment/> 
< / id> 
< property name =countryNamecolumn =c_name/> 
 < / class> 
 
< class name =pojo.PMtable =pm> 
< id name =countryIDcolumn =c_id> 
< generator class =foreign> 
< param name =property> country< / param> 
< / generator> 
< / id> 
< property name =pmNamecolumn =pm_name/> 
< one-to-one class =pojo.Countryname =countryconstrained =true/> 
< / class> 
< / hibernate-mapping> 
  
 POJO类： 
 
 
 国家 
  public class Country {
 private int countryID; 
 private String countryName; 
私人PM下午; 
 
 public PM getPm（）{
 return pm; 
} 
 
 public void setPm（PM pm）{
 this.pm = pm; 
} 
 
 public int getCountryID（）{
 return countryID; 
} 
 
 public void setCountryID（int countryID）{
 this.countryID = countryID; 
} 
 
 public String getCountryName（）{
 return countryName; 
} 
 
 public void setCountryName（String countryName）{
 this.countryName = countryName; 
 
 
  
  PM  
  public class PM {
 private int countryID; 
私人字符串pmName; 
私人国家国家; 
 
 public int getCountryID（）{
 return countryID; 
} 
 
 public void setCountryID（int countryID）{
 this.countryID = countryID; 
} 
 
 public String getPmName（）{
 return pmName; 
} 
 
 public void setPmName（String pmName）{
 this.pmName = pmName; 
} 
 
公共国家getCountry（）{
 return country; 
} 
 
 public void setCountry（Country country）{
 this.country = country; 
} 
 
} 
  
这是试图尝试的类提交事务：
 
 
  public class Runner {
 public static void main（String args []）{System。通过out.println（ dfdf）; 
 Configuration config = new Configuration（）。configure（）; 
 SessionFactory sessFact = config.buildSessionFactory（）; 
会话会话= sessFact.openSession（）; 
 Transaction trans = session.beginTransaction（）; 
国家c =新国家（）; 
 PM pm =新PM（）; 
 pm.setPmName（Manmohan Singh）; 
 c.setCountryName（India）; 
 c.setPm（pm）; 
 
 session.save（c）; 
 trans.commit（）; 
 
 $ b} 
  
   SQL创建表：   
 $ b 
  CREATE TABLE country（c_id INTEGER，c_name TEXT，PRIMARY KEY（c_id ））; 
 CREATE TABLE pm（c_id INTEGER，pm_name TEXT）; 
  
 
 
解决方案
问题在于国家变量。在尝试执行某些事务之前，您应该初始化所有的attirbutes。 
 
 
 
 编辑：在您的Hibernate文件中，您希望从国家/地区的ID生成PM ID。 code>属性。然而，这个属性从未被初始化过。
 < class name =pojo.PMtable =pm> 
< id name =countryIDcolumn =c_id> 
< generator class =foreign> 
< param name =property> country< / param> 
< / generator> 
< / id> 
< property name =pmNamecolumn =pm_name/> 
< one-to-one class =pojo.Countryname =countryconstrained =true/> 
< / class> 
  
因此，添加 pm.setCountry（c）; 添加到您的代码中。
 
As I run my main class (Runner) program I get the following exception :
org.hibernate.id.IdentifierGenerationException: attempted to assign id
from null one-to-one property: country
I don't know the reason, why am I getting this exception.
The mapping xml :
<hibernate-mapping>
  <class name="pojo.Country" table="country">
      <id name="countryID" column="c_id">
          <generator class="increment" />
      </id>
      <property name="countryName" column="c_name" />
      <one-to-one class="pojo.PM" name="pm" cascade="all" />
  </class>

  <class name="pojo.PM" table="pm">
      <id name="countryID" column="c_id">
          <generator class="foreign">
              <param name="property">country</param>
          </generator>
      </id>
      <property name="pmName" column="pm_name" />
      <one-to-one class="pojo.Country" name="country" constrained="true" />
  </class>
</hibernate-mapping>
POJO Classes :
Country
public class Country {
    private int countryID;
    private String countryName;
    private PM pm;

    public PM getPm() {
        return pm;
    }

    public void setPm(PM pm) {
        this.pm = pm;
    }

    public int getCountryID() {
        return countryID;
    }

    public void setCountryID(int countryID) {
        this.countryID = countryID;
    }

    public String getCountryName() {
        return countryName;
    }

    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
}
PM
public class PM {
    private int countryID;
    private String pmName;
    private Country country;

    public int getCountryID() {
        return countryID;
    }

    public void setCountryID(int countryID) {
        this.countryID = countryID;
    }

    public String getPmName() {
        return pmName;
    }

    public void setPmName(String pmName) {
        this.pmName = pmName;
    }

    public Country getCountry() {
        return country;
    }

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

}
and this is the class that tries to commit the transaction :
public class Runner {
    public static void main(String args[]) {System.out.println("dfdf");
        Configuration config = new Configuration().configure();
        SessionFactory sessFact = config.buildSessionFactory();
        Session session = sessFact.openSession();
        Transaction trans = session.beginTransaction();
        Country c = new Country();
        PM pm = new PM();
        pm.setPmName("Manmohan Singh");
        c.setCountryName("India");
        c.setPm(pm);

        session.save(c);
        trans.commit();

    }
}
SQL that created table :
CREATE TABLE country(c_id INTEGER,c_name TEXT,PRIMARY KEY(c_id));
CREATE TABLE pm(c_id INTEGER,pm_name TEXT);
 解决方案 
The problem is the country variable. You should initialize all the attirbutes before trying to do some transactions. 
EDIT: In your Hibernate file, you want to generate the PM ID from the ID of the country property. However, this property has never been initialized.
 <class name="pojo.PM" table="pm">
      <id name="countryID" column="c_id">
          <generator class="foreign">
              <param name="property">country</param>
          </generator>
      </id>
      <property name="pmName" column="pm_name" />
      <one-to-one class="pojo.Country" name="country" constrained="true" />
  </class>
So, add pm.setCountry(c); to your code.
                        
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