java - 级联在 hibernate 模式下无法正常工作

Question

在下面给出的代码中，cascade="save-update"用于与 Student 类关联的 Course 类(包)。

学生类(class)是-->

    private int id;
    private String firstName;
    private String lastName;
    private Address address;
    private List<Course> courses;

类(class)类别是-->

    private int id;
    private String name;
    private int unit;

学生的 hbm 文件是-->

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate.Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="pojos.Student" table="Student">

        <id name="id" type="integer" column="ID">
            <generator class="increment" />
        </id>

        <property name="firstName">
            <column name="FIRST_NAME" />
        </property>

        <property name="lastName">
            <column name="LAST_NAME" />
        </property>

        <many-to-one name="address" 
                     class="pojos.Address" 
                     column="ADDRESS_ID"
                     cascade="save-update" />

        <bag name="courses" inverse="true" cascade="save-update">
            <key column="STUDENT_ID" />
            <one-to-many class="pojos.Course" />
        </bag>

    </class>
</hibernate-mapping>

我正在执行的交易很简单-->

                    Student stud = new Student("Ketan", "Dikshit");
            Address address = new Address("Dm-Road", "Uttar Pradesh", "201301");
            Course course1 = new Course("Core Java", 101);
            Course course2 = new Course("Advanced Java", 201);

            List<Course> courses = new ArrayList<Course>();
            courses.add(course1);
            courses.add(course2);

            stud.setAddress(address);
            stud.setCourses(courses);

            try {
                tr = session.beginTransaction();
                System.out.println("\n Transaction has begun..!!");
                session.save(stud);
                tr.commit();
                System.out.println("\n Transaction is Commit..!!");
                session.close();
                System.out.println("\n Session is Closed..!!");

            } catch (Exception e) {
                System.out.println("\n Transaction is in errror..!!");
                tr.rollback();
                System.out.println("\n Transaction is RollBack..!!");
                session.close();
                System.out.println("\n Session is Closed..!!");
            }

现在，根据代码，类(class)表应该包含一个名为“STUDENT_ID”的列，其中包含类(class)表中每个条目的关联学生的主键。但是“STUDENT_ID”列没有显示任何数据(插入所有空值)。

查询顺序是-->

 Transaction has begun..!!
Hibernate: select max(ID) from Student
Hibernate: select max(ID) from Address
Hibernate: select max(ID) from Course
Hibernate: insert into Address (STREET, CITY, ZIPCODE, ID) values (?, ?, ?, ?)
Hibernate: insert into Student (FIRST_NAME, LAST_NAME, ADDRESS_ID, ID) values (?, ?, ?, ?)
Hibernate: insert into Course (NAME, UNIT, ID) values (?, ?, ?)
Hibernate: insert into Course (NAME, UNIT, ID) values (?, ?, ?)

 Transaction is Commit..!!

为什么类(class)表中的列显示 NULL 值，而不是保存学生的 ID？

Answer 1

从您的包映射中删除 inverse="true"，否则此关系的所有者将是类(class)而不是学生。