java - hibernate/ Spring : Not-null property references a null or transient value

Question

我正在 Java 中使用 Hibernate、Spring 和 GWT 开发一个应用程序。我在 Hibernate 下使用逆向工程(使用 JBoss Developer Studio)从现有 MySQL 数据库中获取 POJO 和配置文件。这是一个非常简单的数据库，只有两个实体:国家和公民。他们之间有OneToMany关系。

代码如下:

应用程序入口点:

...

                    Country country = new Country();
                    country.setName("NameOfCountry"+i);
                    country.setPopulation(10000);

                    Citizen ctz = new Citizen();
                    ctz.setName("John");
                    ctz.setSurname("Smith");


                    ctz.setCountry(country);
                    country.getCitizens().add(ctz);

                    service.saveCitizen(ctz, new AsyncCallback<Boolean>(){

                        @Override
                        public void onFailure(Throwable caught) {
                            System.out.println("Problem saving citizen");

                        }

                        @Override
                        public void onSuccess(Boolean result) {
                            System.out.println("Citizen successfully saved");

                        }

                    });

                    service.saveCountry(country, new AsyncCallback<Boolean>(){

                        @Override
                        public void onFailure(Throwable caught) {
                            System.out.println("Problem saving country");

                        }

                        @Override
                        public void onSuccess(Boolean result) {
                            System.out.println("Country successfully saved");

                        }
                    });

...

-- 服务向服务器提供简单的 GWT-RPC 调用

服务器上的服务:

@Service("componentService")
public class ComponentServiceImpl implements ComponentService{

    @Autowired
    private CountryDAO daoCnt;

    @Autowired
    private CitizenDAO daoCtz;

    @Transactional(readOnly=false)
    @Override
    public boolean saveCitizen(Citizen citizen) {
        daoCtz.saveOrUpdate(citizen);
        return true;
    }

    @Transactional(readOnly=false)
    @Override
    public boolean saveCountry(Country country) {
        daoCnt.saveOrUpdate(country);
        return true;
    }
}

现在 SpringDAO:

CitizenDAO:

@Repository
public class CitizenDAO {

...
    public void saveOrUpdate(Citizen citizen){
        sessionFactory.getCurrentSession().saveOrUpdate(citizen);
    }
...

CountryDAO:

@Repository
public class CountryDAO {

...
    public void saveOrUpdate(Country country){
        sessionFactory.getCurrentSession().saveOrUpdate(country);
    }
...

终于

Citizen.hbm.xml:

<hibernate-mapping>
    <class name="sk.jakub.mod.shared.model.Citizen" table="citizen" catalog="modeldb">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="identity" />
        </id>
        <many-to-one name="country" class="sk.jakub.mod.shared.model.Country" fetch="select">
            <column name="Country_id" not-null="true" />
        </many-to-one>
        <property name="name" type="string">
            <column name="name" length="45" not-null="true" />
        </property>
        <property name="surname" type="string">
            <column name="surname" length="45" not-null="true" />
        </property>
    </class>
</hibernate-mapping>

Country.hbm.xml:

<hibernate-mapping>
    <class name="sk.jakub.mod.shared.model.Country" table="country" catalog="modeldb">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="identity" />
        </id>
        <property name="name" type="string">
            <column name="name" length="45" not-null="true" />
        </property>
        <property name="population" type="int">
            <column name="population" not-null="true" />
        </property>
        <set name="citizens" table="citizen" inverse="true" lazy="true" fetch="select">
            <key>
                <column name="Country_id" not-null="true" />
            </key>
            <one-to-many class="sk.jakub.mod.shared.model.Citizen" />
        </set>
    </class>
</hibernate-mapping>

我没有列出 Citizen.java 和 Country.java，因为它们只是基本的 POJO(如果需要，我会提供它们)。

当我启动应用程序并且想要将数据保存到数据库中时，出现以下错误:

org.hibernate.PropertyValueException: not-null property references a null or transient value: sk.jakub.mod.shared.model.Citizen.country 

我不知道问题出在哪里。我也尝试用 persist 方法代替 saveOrUpdate 方法。或者也可以更改保存到数据库的顺序。似乎没有任何效果。

非常感谢您的帮助:)如果需要，我可以从我的应用程序中发布更多代码。

编辑:Citizen.java 代码:

public class Citizen implements java.io.Serializable {

    private static final long serialVersionUID = -3102863479088406293L;
    private Integer id;
    private Country country;
    private String name;
    private String surname;

    public Citizen() {
    }

    public Citizen(Country country, String name, String surname) {
        this.country = country;
        this.name = name;
        this.surname = surname;
    }

    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Stat getCountry() {
        return this.country;
    }

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

    public String getName() {
        return this.name;
    }

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

    public String getSurname() {
        return this.surname;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }
}

国家.java:

public class Country implements java.io.Serializable {

    private static final long serialVersionUID = -4085805854508658303L;
    private Integer id;
    private String name;
    private int population;
    private Set<Citizen> citizens = new HashSet<Citizen>();

    public Country() {
    }

    public Country(String name, int population) {
        this.name = name;
        this.population = population;
    }

    public Country(String name, int population, Set<Citizen> citizens) {
        this.name = name;
        this.population = population;
        this.citizens = citizens;
    }

    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return this.name;
    }

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

    public int getPopulation() {
        return this.population;
    }

    public void setPopulation(int population) {
        this.population = population;
    }

    public Set<Citizen> getCitizens() {
        return this.citizens;
    }

    public void setCitizens(Set<Citizen> citizens) {
        this.citizens = citizens;
    }
}

此外，我手动检查了数据库，国家已保存，但公民未保存。

Answer 1

我看到您在创建国家之前先创建公民。此外，两个服务调用都应该在同一事务中，以使整个操作具有原子性。我相信 COUNTRY_ID 似乎是一个自行生成的 ID。因此，一旦创建了国家/地区，您就可以将其附加到公民，但是调用堆栈显示您正在创建一个公民，该公民具有一个没有 id 的国家/地区对象。这只是我的猜测。您可以尝试将这两个调用放在同一事务下，还可以尝试创建一个国家/地区并将该国家/地区实例附加到公民。