使用条件查询检索多态 Hibernate 对象
在我的模型中，我有一个抽象的“User”类和多个子类，例如 Applicant、HiringManager 和 Interviewer。它们位于一个表中，我有一个 DAO 来管理它们。
用户：
@Entity
@Table(name="User")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(
name="role",
discriminatorType=DiscriminatorType.STRING
)
public abstract class User extends BaseObject implements Identifiable<Long> ...
HiringManager（例如）：
@Entity
@DiscriminatorValue("HIRING_MANAGER")
public class HiringManager extends User ...
现在，如果我想获取与某个部门无关的所有招聘经理，我该怎么做？我想象它看起来像这样：
DetachedCriteria c = DetachedCriteria.forClass(User.class);
c.add(Restrictions.eq("role", "HIRING_MANAGER"));
c.add(Restrictions.isNull("department"));
List<User> results = getHibernateTemplate().findByCriteria(c);
但是当我运行这个时，Hibernate 抱怨“无法解析属性：角色”（这实际上是有道理的，因为 User 类确实没有显式的角色属性）
那么做我想做的事情的正确方法是什么？
In my model I have an abstract "User" class, and multiple subclasses such as Applicant, HiringManager, and Interviewer. They are in a single table, and I have a single DAO to manage them all.
User:
@Entity
@Table(name="User")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(
name="role",
discriminatorType=DiscriminatorType.STRING
)
public abstract class User extends BaseObject implements Identifiable<Long> ...
HiringManager (for example):
@Entity
@DiscriminatorValue("HIRING_MANAGER")
public class HiringManager extends User ...
Now if I wanted to, say, get all the hiring managers that are not associated with a department, how would I do that? I imagine it would look something like:
DetachedCriteria c = DetachedCriteria.forClass(User.class);
c.add(Restrictions.eq("role", "HIRING_MANAGER"));
c.add(Restrictions.isNull("department"));
List<User> results = getHibernateTemplate().findByCriteria(c);
But when I run this, Hibernate complains "could not resolve property: role" (Which actually makes sense because the User class really doesn't have an explicit role property)
So what's the right way to do what I'm trying to do?
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我可能遗漏了一些明显的东西，但既然您想找到招聘经理，为什么不将
HiringManager子类作为类传递给Criteria呢？为了以防万一，有一个特殊的
class属性可用于将查询限制为子类型。来自 Hibernate 参考文档：您也可以将这个特殊的类属性与 Criteria API 一起使用，但需要进行一个小的更改：您必须使用鉴别器值作为值。
与 HQL 不同，Hibernate 似乎没有使用 Criteria API 进行转换。我真的不喜欢在代码中使用鉴别器值的想法，也许还有另一种更干净的方法，但我不知道。但它有效。
I may be missing something obvious but since you want to find hiring managers, why don't you just pass the
HiringManagersubclass as the class to theCriteria?Just in case, there is a special
classproperty that you can use to restrict a query to a subtype. From the Hibernate reference documentation:You can use this special class property with the Criteria API too, but with a minor change: you have to use the discriminator value as value.
Unlike with HQL, it looks like Hibernate is not doing the translation with the Criteria API. I don't really like the idea of using the discriminator value in the code and there is maybe another cleaner way but I'm not aware of it. But it works.
请注意，这也适用于连接子类继承映射，但有一点需要注意。限制中使用的类必须是具体类。如果您有像 Animal <- Mammal <- Cat 这样的模型，则无法执行
Restrictions.eq("class", Mammal.class);并期望返回所有哺乳动物。相反，我必须使用 Restrictions.or 和所有已知的具体类来暴力破解它（使用 Restrictions.in() 在执行查询时给出了类转换异常）。Note that this also works for Joined Subclass inheritance mappings, with one caveat. The class used in the Restriction must be a concrete class. If you have a model like Animal <- Mammal <- Cat, you cannot do
Restrictions.eq("class", Mammal.class);and expect to get back all Mammals. Instead, I had to brute force it using Restrictions.or with all known concrete classes (using Restrictions.in() gave a class cast exception when executing the query).