这个bug是在使用hibernate annotation过程中发现的，开始以为是hibenrate annotation的bug，后来又使用xml文件来配置，还是存在同样的问题。
问题场景：我需要使用省份与城市，他们的关系是：一个省有个多城市，很简单的OneToMany关系，在改变province中的cities的lazy特性时，遇到问题
由于我采用把所有的资源都是放在一个表中的策略，所有这里有一个基类Resource
基类
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = " CATEGORY_ID " , discriminatorType = DiscriminatorType.STRING)
@Table(name = " T_RESOURCE " )
public class Resource implements Serializable ... {
private String id;
private String name;
private ResourceCategory resourceCategory;
@Id
@GenericGenerator(name = "generator", strategy = "uuid")
@GeneratedValue(generator = "generator")
@Column(name = "ID")
public String getId() ...{
return id;
}
@Column(name = "NAME")
public String getName() ...{
return name;
}
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "CATEGORY_ID", updatable = false, insertable = false)
public ResourceCategory getResourceCategory() ...{
return resourceCategory;
}
@Override
public boolean equals(final Object other) ...{
if (!(other instanceof Resource))
return false;
Resource castOther = (Resource) other;
return new EqualsBuilder().append(id, castOther.id).isEquals();
}
@Override
public int hashCode() ...{
return new HashCodeBuilder().append(id).toHashCode();
}
}
Province子类
@Entity
@DiscriminatorValue( " province " )
public class Province extends Resource ... {
private Set<City> cities = new HashSet<City>();
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "province")
public Set<City> getCities() ...{
return cities;
}
}
子类City
@Entity
@DiscriminatorValue( " city " )
public class City extends Resource ... {
private Province province;
public City(String name, ResourceCategory resourceCategory) ...{
super(name, resourceCategory);
}
@ManyToOne
@JoinColumn(name = "PARENT_ID")
public Province getProvince() ...{
return province;
}
}
hibernate.cfg.xml
<!--
<mapping resource="ResourceCategory.hbm.xml" />
<mapping resource="Resource.hbm.xml" />
-->
< mapping class ="ResourceCategory" />
< mapping class ="Resource" />
hibernate助手类
public class HibernateUtil ... {
private static SessionFactory sessionFactory;
static ...{
// Configuration configuration = new Configuration();
AnnotationConfiguration configuration = new AnnotationConfiguration();
configuration.configure();
sessionFactory = configuration.buildSessionFactory();
}
public static SessionFactory getSessionFactory() ...{
return sessionFactory;
}
public Session getSession() ...{
return getSessionFactory().openSession();
}
}
单元测试类
public class HibnerateTest extends TestCase ... {
public void testListProvinceByHQL() ...{
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.openSession();
Transaction ctx = session.beginTransaction();
Query query = session.createQuery("from Province");
List<Province> provinces = query.list();
for (Province province : provinces) ...{
System.out.println(province.getName());
}
ctx.commit();
}
public void testListProvinceByCriteria() ...{
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.openSession();
Transaction ctx = session.beginTransaction();
Criteria criteria = session.createCriteria(Province.class);
List<Province> provinces = criteria.list();
for (Province province : provinces) ...{
System.out.println(province.getName());
}
ctx.commit();
}
}
分别执行单元测试方法，他们输出的sql语句是一样的，但是输出的结果是不一样的。
select this_.ID as ID1_1_, this_.NAME as NAME1_1_, this_.COMMENTS as COMMENTS1_1_, this_.CATEGORY_ID as CATEGORY2_1_1_, cities2_.PARENT_ID as PARENT5_3_, cities2_.ID as ID3_, cities2_.ID as ID1_0_, cities2_.NAME as NAME1_0_, cities2_.COMMENTS as COMMENTS1_0_, cities2_.CATEGORY_ID as CATEGORY2_1_0_, cities2_.PARENT_ID as PARENT5_1_0_ from T_RESOURCE this_ left outer join T_RESOURCE cities2_ on this_.ID=cities2_.PARENT_ID where this_.CATEGORY_ID='province'
testListProvinceByHQL方式输出的是
上海
上海
上海
上海
江苏
江苏
江苏
江苏
testListProvinceByCriteria方式输出的是
上海
江苏
若把public Set<City> getCities()的映射改为
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "province")
@Fetch(FetchMode.SELECT)
或者
@OneToMany(cascade = CascadeType.ALL, mappedBy = "province")
@LazyCollection(LazyCollectionOption.FALSE)
则两个方法输出sql语句是一样的，且结果也一样
SQL:
select this_.ID as ID1_0_, this_.COMMENTS as COMMENTS1_0_, this_.NAME as NAME1_0_, this_.CATEGORY_ID as CATEGORY1_1_0_ from T_RESOURCE this_ where this_.CATEGORY_ID='province'
select cities0_.PARENT_ID as PARENT5_1_, cities0_.ID as ID1_, cities0_.ID as ID1_0_, cities0_.COMMENTS as COMMENTS1_0_, cities0_.NAME as NAME1_0_, cities0_.CATEGORY_ID as CATEGORY1_1_0_, cities0_.PARENT_ID as PARENT5_1_0_ from T_RESOURCE cities0_ where cities0_.PARENT_ID=?
select cities0_.PARENT_ID as PARENT5_1_, cities0_.ID as ID1_, cities0_.ID as ID1_0_, cities0_.COMMENTS as COMMENTS1_0_, cities0_.NAME as NAME1_0_, cities0_.CATEGORY_ID as CATEGORY1_1_0_, cities0_.PARENT_ID as PARENT5_1_0_ from T_RESOURCE cities0_ where cities0_.PARENT_ID=?
输出：
上海
江苏
从上面的现象可是看出，不论配置文件怎么变化，通过hql语句获得结果一直不变，而Criteria会变化，这就证明了Criteria是有bug的。
据此我得出结论:hibernate的Criteria在把关联的lazy属性设置为"false"，且把fetch设置为join时，查找数据就存在bug
后来我使用xml配置文件的方式，也存在同样的问题，也证明了我的这个结论，
Resource.hbm.xml
<? 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 ="Resource"
table ="T_RESOURCE" >
< id name ="id" type ="string" >
< column name ="ID" />
</ id >
< discriminator column ="CATEGORY_ID" type ="string" />
< property name ="name" type ="string" column ="NAME" />
< many-to-one name ="resourceCategory" insert ="false"
update ="false"
class ="ResourceCategory"
column ="CATEGORY_ID" />
< subclass name ="Province"
discriminator-value ="province" >
< set name ="cities" lazy ="false" fetch ="join" >
< key >
< column name ="PARENT_ID" />
</ key >
< one-to-many class ="City" />
</ set >
</ subclass >
< subclass name ="City"
discriminator-value ="city" >
< many-to-one name ="province"
class ="Province"
column ="PARENT_ID" />
</ subclass >
</ class >
</ hibernate-mapping >
ResourceCategory.hbm.xml
<? 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 = " ResourceCategory "
table = " T_RESOURCE_CATEGORY " >
< id name = " id " type = " string " >
< column name = " ID " />
</ id >
< property name = " name " type = " string " column = " NAME " />
</ class >
</ hibernate - mapping >