[英]Using HQL to select from joined tables having one to many relationship between them
我一直沉迷於休眠狀態,不知道如何解決。 請幫忙 !
所以我有兩個表:
POSITION
positionid(PK), description
JOB
jobid(PK),positionid(FK),description
如何在Hibernate中使用HQL來獲取所有作業及其相應的位置描述?
編輯:所以這是我想要實現的:
JOBID POSITION.DESCRPTION JOB.DESCRIPTION
1 Teacher Science Teacher
2 Coach Football Coach
以此類推,對於JOB表中的所有作業。 我試圖弄清楚這將是HQL。
到目前為止,我已經整理了以下代碼:
position.hbm.xml
<hibernate-mapping>
<class name="com.XXXX.model.Position" table="POSITION">
<id name="positionID" type="int" column="POSITIONID" >
<generator class="assigned"/>
</id>
<property name="description">
<column name="DESCRIPTION" />
</property>
<set name="jobs">
<key column="positionID" />
<one-to-many class="com.XXXX.model.Job" />
</set>
</class>
</hibernate-mapping>
job.hbm.xml
<hibernate-mapping>
<class name="com.XXXX.model.Job" table="JOB">
<id name="jobID" type="int" column="JOBID" >
<generator class="assigned"/>
</id>
<property name="description">
<column name="DESCRIPTION" />
</property>
<many-to-one name="position" class="com.XXXX.model.Position" column="positionID" />
</class>
</hibernate-mapping>
Position.java
public class Position {
private int positionID;
private String description;
private Set<Job> jobs = new HashSet<Job>();
// Getters and Setters for all the above three follows...
}
Job.java
public class Job {
private int jobID;
private String description;
private Position position;
// Getters and Setters for all the above three follows...
}
現在在我的代碼中使用
session.createQuery("from Position as p left join p.positionID as pid").list();
我知道它不完全正確,並且出現以下錯誤:
java.lang.NullPointerException
at org.hibernate.hql.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:317)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3268)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3060)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:2938)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:688)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:544)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:281)
.........................
...........................
有人可以告訴我如何解決這個問題嗎?
如果只需要這三列,則HQL應該是
select job.id, position.decription, job.description
from Job job
left join job.position position
該查詢將返回List<Object[]>
,列表中的每個Object數組將包含這三個元素。
但是使用以下查詢會自然得多:
select job from Job job
left join fetch job.position
這將加載所有作業的位置。 該查詢將返回一個List,您將能夠使用job.getId()
, job.getPosition().getDescription()
和job.getDescription()
來訪問三個信息。
必須閱讀的參考文檔中的示例介紹了HQL的語法。
我認為您只能從Position對象獲取getJobs()
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