[英]How to select parent objects without children in Hibernate?
我有以下实体,父对象和子对象,父对象可能没有子对象。 如何选择没有孩子休眠的父母? 它类似于 SQL 中not existing
子句。 这是我的实体:
@Entity
@Table(name = "PARENT")
public class Parent implements Serializable {
@Id
@Column(name="PARENT_ID")
private Long parentId;
@Column(name="NAME")
private String name;
@OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
Set<Child> children;
}
@Entity
@Table(name = "CHILD")
public class Child implements Serializable {
@Id
@Column(name="CHILD_ID")
private Long childId;
@Column(name="NAME")
private String name;
@ManyToOne(cascade={CascadeType.ALL}, fetch=FetchType.EAGER)
@JoinColumn(name="PARENT_ID", nullable=false, updatable=false)
private Parent parent;
}
我的查询:
public List<Parent> getParentsNotHavingChildren() {
Session session = this.sessionFactory.getCurrentSession();
Transaction txn = session.beginTransaction();
List<Parent> result = null;
Criteria criteria = session.createCriteria(Parent.class)
.add(Restrictions.eq("children", null));
result = criteria.list();
txn.commit();
if (session.isOpen()) {
session.close();
}
log.info(String.format("Get %s parents", result.size()));
return result;
}
然后我得到了错误
org.hibernate.exception.GenericJDBCException: could not execute query
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:140)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:128)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.loader.Loader.doList(Loader.java:2545)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
at org.hibernate.loader.Loader.list(Loader.java:2271)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)
at HibernateParentDao.getParentsNotHavingChildren(HibernateParentDao.java:42)
Caused by: java.sql.SQLException: Missing IN or OUT parameter at index:: 1
at oracle.jdbc.driver.SQLStateMapping.newSQLException(SQLStateMapping.java:70)
at oracle.jdbc.driver.DatabaseError.newSQLException(DatabaseError.java:110)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:171)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:227)
at oracle.jdbc.driver.OraclePreparedStatement.processCompletedBindRow(OraclePreparedStatement.java:1737)
at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3376)
at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:3425)
at oracle.jdbc.driver.OraclePreparedStatementWrapper.executeQuery(OraclePreparedStatementWrapper.java:1202)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeQuery(NewProxyPreparedStatement.java:76)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1953)
at org.hibernate.loader.Loader.doQuery(Loader.java:802)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.doList(Loader.java:2542)
我确定我的标准不正确,但我找不到此类查询的正确方法。 任何帮助将不胜感激!
要测试一个属性为空,然后使用isNull
...更改
Criteria criteria = session.createCriteria(Parent.class)
.add(Restrictions.eq("children", null));
对于
Criteria criteria = session.createCriteria(Parent.class)
.add(Restrictions.isNull("children"));
否则,Hibernate 将期望一个非空值来执行eq
这是选择没有子级的父级的简单标准(对于一对多关系,您应该使用isEmpty
)。
Criteria criteria = currentSession().createCriteria(Parent.class);
criteria.add(Restrictions.isEmpty("children"));
return criteria.list();
顺便说一下,对于简单的“选择”查询,您不需要创建transaction
。 只要有上面的三行就足够了。
另一个答案可能有效,但仅适用于一对一的关系。 希望它有效!
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.