java - 一对多双向关系在内存 HSQL DB 中不起作用

Question

我有一个城市和人之间的一对多映射。一个城市可以有很多人。持久化数据后，从 hibernate 中获取 People 对象时，我也获取了城市对象。城市是父表/实体。但是在使用 hibernate 获取 city 对象时，people 对象(集合或列表)是空的。对 MYSQL DB 尝试使用相同的代码时效果很好。但是在内存数据库中使用 HSQL 时，我遇到了这个问题。PFB 详细信息:-

城市实体:-

@Entity
@Table(name="CITY")
public class City {
    @Id
    @GeneratedValue
    @Column(name="CITY_ID")
    private long id;
    @Column(name="CITY_NAME", nullable=false, unique= true)
    private String name;

    @OneToMany(fetch = FetchType.EAGER, mappedBy = "city" )
    private Set<People> people = new HashSet<People>(0);

人员实体:-

@Entity
@Table(name="People")
public class People {
    @Id
    @GeneratedValue
    @Column(name="People_ID")
    private long id;
    @Column(name="People_NAME", nullable=false, unique= true)
    private String name;
    @ManyToOne
    @JoinColumn(name = "CITY_ID")
    City city;

我将首先向 City 表插入值。示例值:-("London")..如果生成的 cityid 为“1001”，则在坚持之后然后将值插入 people 表。示例值:-("John",1001)然后在使用 hibernate 获取 City 对象的值时，people(set) 为空。但是，如果我获取 People 对象的值，则 city 对象具有值。PFb 我的 xml 文件:-

<bean id="dataSource"
            class="org.springframework.jdbc.datasource.DriverManagerDataSource">
            <property name="driverClassName" value="org.hsqldb.jdbcDriver" />
            <property name="url" value="jdbc:hsqldb:TEST" />
            <property name="username" value="sa" />
            <property name="password" value="" />
        </bean>
        <bean id="sessionFactory"                class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
            <property name="dataSource" ref="dataSource" />
            <property name="packagesToScan" value="entity" />
            <property name="hibernateProperties">
                <props>
                    <prop key="hibernate.dialect">org.hibernate.dialect.HSQLDialect</prop>
                    <prop key="hibernate.hbm2ddl.auto">create-drop</prop>
                    <prop key="hibernate.show_sql">true</prop>
                </props>
            </property>
        </bean>

        <bean id="transactionManager"
            class="org.springframework.orm.hibernate3.HibernateTransactionManager">
            <property name="sessionFactory" ref="sessionFactory" />
        </bean>
        <tx:annotation-driven transaction-manager="transactionManager" />        
    </beans>

这是内存数据库的限制，还是我遗漏了什么。任何建议或链接都​​会有帮助

Answer 1

我最近创建了一个示例应用程序来演示这种使用 hibernate 的关系，下面是它的代码。

@Entity
@Table(name = "COMPANY")
public class Company {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column(name = "COMP_NAME", length = 1000)
    private String companyName;
    @Column(name = "COMP_ADDRESS", length = 1000)
    private String companyAddress;
    @OneToOne(mappedBy = "company")
    private Employee emp;

    @OneToMany
    private Set<Department> departments = new HashSet<Department>();

    public Set<Department> getDepartments() {
        return departments;
    }

    public void setDepartments(Set<Department> departments) {
        this.departments = departments;
    }

下面是我的Department.java

@Entity
@Table(name = "DEPARTMENT")
public class Department {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String deptName;
    @ManyToOne
    private Company company;

    public Company getCompany() {
        return company;
    }

    public void setCompany(Company company) {
        this.company = company;
    }

请注意，我没有使用 @JoinColumn，这导致了关系表的创建，只需从您的 People 类中删除 @JoinColumn，您就会从 City 类中获取人员集合。