mysql如何在Java程序中使用Hibernate？

Question

我有 Query for fetch two tables data combined

我正试图在使用Hibernate3的Java程序中使用它。 每当我试图获取数据时，我都会遇到异常。 我的完整代码在Question in Coderanch, 1st reply have complete java, xml files.中

这里是我在java程序中使用的查询

String selectQuery = "select student.roll_no, student.name, exam_dates.subject, exam_dates.date "
    + "from student student "
    + "JOIN exam_dates exam_dates on exam_dates.roll_no = student.roll_no";

还有一个要审判

  String selectQuery = "select student.roll_no, student.name, exam_dates.subject, exam_dates.date "
            + "from student student "
            + "INNER JOIN exam_dates exam_dates on exam_dates.roll_no = student.roll_no";

通过使用它，我得到如下异常：-

14:19:07,752  INFO MemoryContextFactory:34 - Creating EJB3Unit initial JNDI context
org.hibernate.QueryException: outer or full join must be followed by path expression [select student.roll_no, student.name, exam_dates.subject, exam_dates.date from student student INNER JOIN exam_dates exam_dates on exam_dates.roll_no = student.roll_no]
at org.hibernate.hql.classic.FromParser.token(FromParser.java:170)
at org.hibernate.hql.classic.ClauseParser.token(ClauseParser.java:86)
at org.hibernate.hql.classic.PreprocessingParser.token(PreprocessingParser.java:108)
at org.hibernate.hql.classic.ParserHelper.parse(ParserHelper.java:28)
at org.hibernate.hql.classic.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:216)
at org.hibernate.hql.classic.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:185)
at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:77)
at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56)
at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:72)
at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:133)
at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:112)
at org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1623)
at test_db.get_table_by_join(test_db.java:99)
at test_db$1.run(test_db.java:40)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

有人能帮我吗

Answer 1

将实体类创建为

@Entity
public class Student{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long rollNo;
    private String name;
    @OneToMany
    private ExamDates examDates;

    public void setRollNo(Long rollNo) {
        this.rollNo = rollNo;
    }

    public void getRollNo() {
        return this.rollNo;
    }

    public String getName() {
        return name;
    }

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

    public String getExamDates() {
        return this.examDates;
    }

    public void setExamDates(ExamDates examDates) {
        this.examDates = examDates;
    }
}

ExamDates是另一个映射到考试日期表的类。你什么时候打电话

Student s = entityManager.find(Student.class, rollNo); 

它会给你学生对象，然后调用s.getExamDates，它会给你考试日期