cats_tiger

前一个关于这个问题的帖子被隐藏了，这次说明确些。
例如有两个类，员工TestEmployee 和部门TestDept，它们是ManyToOne关系：

@Entity
@Table(name = "test_employees", uniqueConstraints = { })
public class TestEmployee extends BaseModel implements Serializable {
  private Integer id;
  private TestDept dept;

  @Id
  @GeneratedValue(generator = "hilo")
  @GenericGenerator(name = "hilo", strategy = "hilo")
  @Column(name = "ID", unique = true, nullable = false)
  public Integer getId() {
    return this.id;
  }

  public void setId(Integer id) {
    this.id = id;
  }

  @ManyToOne(cascade = { }, fetch = FetchType.LAZY)
  @JoinColumn(name = "dept_id")
  public TestDept getDept() {
    return this.dept;
  }

  public void setDept(TestDept dept) {
    this.dept = dept;
  }
}
@Entity
@Table(name = "test_depts", uniqueConstraints = { })
public class TestDept extends BaseModel implements Serializable {
  
  private Integer id;
  private String name;
  private Set<TestEmployee> employees = new HashSet<TestEmployee>(0);

  @Id
  @GeneratedValue(generator = "hibseq")
  @GenericGenerator(name = "hibseq", strategy = "hilo")
  @Column(name = "ID", unique = true, nullable = false)
  public Integer getId() {
    return this.id;
  }

  public void setId(Integer id) {
    this.id = id;
  }


  @Column(name = "name")
  public String getName() {
    return this.name;
  }

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

  @OneToMany(cascade = { }, fetch = FetchType.LAZY, mappedBy = "dept")
  public Set<TestEmployee> getEmployees() {
    return this.employees;
  }

  public void setEmployees(Set<TestEmployee> employees) {
    this.employees = employees;
  }
}

现在我要查询员工A所在的部门，使用隐含关联：

getHibernateTemplate().find(
        "from TestDept d where d.employees.name = 'A'");

如果使用Hibernate3.2.3以后的版本，会出现一个异常illegal attempt to dereference collection。这个问题比较容易解决，只需要明确的关联上employees即可：

getHibernateTemplate().find(
        "from TestDept d inner join d.employees e where e.name = 'A'");

可是，如果使用Hibernate3.2.2，即使使用隐含关联也不会有问题。我的问题是：现在升级为Hibernate3.2.5，以前的代码怎么办？这是Hibernate的Bug吗？
从Hibnerate的Jira上终于得到了答案：
对于implicit joins，Hibernate3.2.2会自动生成inner join，这样，被关联对象如果为null，就不会查出任何结果。这使得隐含关联更具确定性（原文：This makes implicit joins more deterministic. ）。
Hibernate3.2.2之后如果隐含关联的是一个Collection，那么Hibernate就会抛出那个异常。这会提醒用户，使用更加明确的关联。
终于弄清问题所在了，可是以前的代码都得改，JUnit测出了40多个Bugs，郁闷呀！

getHibernateTemplate().find("from TestDept d where d.employees.name = 'A'");  

getHibernateTemplate().find("from TestEmployee e where e.testDept.name = 'B'");  

getHibernateTemplate().find("from TestDept d where d.employees.name = 'A'");  

getHibernateTemplate().find("from TestEmployee e where e.testDept.name = 'B'");