休眠一對一映射問題

Question

我有以下兩節課：

public class User {

    private int id;
    private String name;
    private ProteinData proteinData;

    public User(){
        setProteinData(new ProteinData());
    }

    public ProteinData getProteinData() {
        return proteinData;
    }
    public void setProteinData(ProteinData proteinData_) {
        this.proteinData = proteinData_;
        proteinData_.setUser(this);
    }

   // additional getters and setters

}


public class ProteinData {

    private int id;
    private User user;


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

    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
}

映射文件為：

//User
<hibernate-mapping>
   <class name="com.simpleprogrammer.User" table="USERS">
      <meta attribute="class-description">
         This class contains the User detail. 
      </meta>
      <id name="id" type="int">
         <column name="ID" />
         <generator class="identity"/>
      </id>
      <property name="name" type="java.lang.String">
         <column name="NAME" />
      </property>

      <one-to-one name="proteinData" class="com.simpleprogrammer.ProteinData" cascade="save-update"/>
</hibernate-mapping>

// proteinData
<hibernate-mapping>
   <class name="com.simpleprogrammer.ProteinData" table="PROTEINDATA">
        <id name="id" type="int">
            <column name="ID" />
            <generator class="foreign">
                <param name="property">user</param>
            </generator>
        </id>
        <one-to-one name="user" class="com.simpleprogrammer.User" constrained="true">
        </one-to-one>
        <property name="total" type="int" column="TOTAL" />
        <property name="goal" type="int">
            <column name="GOAL"/>
        </property>
   </class>
</hibernate-mapping>

現在，當我運行我的應用程序時，出現以下錯誤：

Exception in thread "main" org.hibernate.PropertyAccessException: Exception occurred inside setter of com.simpleprogrammer.User.proteinData
    at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:88)
    at org.hibernate.tuple.entity.AbstractEntityTuplizer.setPropertyValues(AbstractEntityTuplizer.java:710)
    at org.hibernate.tuple.entity.PojoEntityTuplizer.setPropertyValues(PojoEntityTuplizer.java:371)
    at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:4509)
    at org.hibernate.engine.internal.TwoPhaseLoad.doInitializeEntity(TwoPhaseLoad.java:186)
    at org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:137)
    at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1108)
    at org.hibernate.loader.Loader.processResultSet(Loader.java:964)
    at org.hibernate.loader.Loader.doQuery(Loader.java:911)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:342)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:312)
    at org.hibernate.loader.Loader.loadEntity(Loader.java:2121)
    at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:82)
    at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:72)
    at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3927)
    at org.hibernate.event.internal.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:460)
    at org.hibernate.event.internal.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:429)
    at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:206)
    at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:145)
    at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1092)
    at org.hibernate.internal.SessionImpl.immediateLoad(SessionImpl.java:1007)
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:173)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    at com.simpleprogrammer.User_$$_javassist_0.getName(User_$$_javassist_0.java)
    at com.pluralsight.Introduction_To_Hibernate_Pluralsight.Program.main(Program.java:45)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:65)
    ... 25 more
Caused by: java.lang.NullPointerException
    at com.simpleprogrammer.User.setProteinData(User.java:44)
    ... 30 more

該錯誤來自User類中的setProteinData()方法。 錯誤中的最后一條語句顯示java.lang.NullPointerException並指向該方法。 我不知道我在做什么錯。

Answer 1

我認為問題在於，ProteinData類中沒有空（無參數）構造函數。 嘗試將其添加到類中：

public ProteinData(){}

Answer 2

刪除對proteinData_.setUser(this);調用proteinData_.setUser(this); 從setProteinData方法。 不需要。

此外，您可以使用無參數構造函數public ProteinData(){}或者即使您不使用無參數構造函數，也可以，如果沒有其他構造函數（無參數或構造函數），編譯器將創建默認構造函數帶有參數）。

你可以閱讀有關休眠無參數的構造需要更多的討論在這里 。