具有单表继承的子类的 JPA 查询

Question

假设我有以下实体：

@Entity
public class Container
{
    @OneToMany
    Set<AbstractElement> elements;

    //getter setter and other attributes...
}

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "CLASS_CODE", discriminatorType = DiscriminatorType.STRING, length = 10)
public abstract class AbstractElement<T> extends AbstractEntity
{
    @Transient
    T value;

    //getter setter and other attributes...
}

@DiscriminatorValue(value = "BOOL")
@Entity
public class BooleanElement extends AbstractElement<Boolean>
{
    /**
     * {@inheritDoc}
     */
    @Column(name = "VALUE_BOOL")
    @Override
    public Boolean getValue()
    {
        return super.getValue();
    }
}

问题是这样的：

如何从 class CONTAINER 开始对 BooleanElement 的值执行 jpa 条件查询？

到目前为止我实际拥有的是：

CriteriaQuery<Container> criteriaQuery = criteriaBuilder.createQuery(Container.class);
Root<Container> from = criteriaQuery.from(Container.class);
criteriaQuery.select(from);
from = from.join("elements");
Predicate pred = criteriaBuilder.equal(criteriaBuilder.treat(from ,BooleanElement.class).get("value"), FOO);

//etc......

此时的例外是"there is not VALUE attributes on the AbstractEntity"。

提前致谢。

Answer 1

在此特定情况下，Treat 运算符不起作用。连接上的 as 运算符它仍然不太清楚如何实现：我在第 3 行执行此操作时得到 class 强制转换异常：

CriteriaQuery<AbstractElement> criteriaQuery = criteriaBuilder.createQuery(AbstractElement.class);
Root<AbstractElement> rootAbstract = criteriaQuery.from(AbstractElement.class);
Path predPath = (Path)rootAbstract.as(BooleanElement.class);
predPath.get("value");

执行此类查询的唯一方法是执行子查询或创建一个额外的 "from" 子句：

Root<BooleanElement> from2 = criteriaQuery.from(BooleanElement.class);
Predicate joinPredicate = criteriaBuilder.equal(from, from2);
....

具有单表继承的子类的 JPA 查询

JPA Query on sublclass with SingleTable inheritance

java

jpa

criteria-api

java-ee-7

jakarta-ee