Java QueryDSL继承：where子句中的子类型

我正在尝试创建一个查询，它应该返回子类型（InternalTask和ExternalTask的列表）。这非常有效，但我想在查询中为其中一个子类型添加where子句。我尝试了以下方法：

实体：

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "TASK_TYPE")
public abstract class Task {
    ...
}

@Entity
@DiscriminatorValue("INTERNAL")
public class InternalTask extends Task {
    ...
    private Employee employee;
    ...
}

@Entity
@DiscriminatorValue("EXTERNAL")
public class ExternalTask extends Task {
    ...
}

功能：

public List<? extends Task> findTasks(TaskSearch taskSearch) {
    JPAQuery query = new JPAQuery(entityManager);

    QTask task = QTask.task;
    BooleanBuilder where = new BooleanBuilder();

    if (taskSearch.getEmployee() != null) {
        where.and(task.instanceOf(InternalTask.class).and(task.as(QInternalTask.class).employee.eq(taskSearch.getEmployee())));
    }

    query.from(task).where(where).orderBy(task.deadline.asc());

    return query.list(task);
}

---

正如您所看到的，它被转换为任务实体上的select，该实体不知道子类型InternalTask。有没有办法在子类型上实现where子句？

我通过添加子查询找到了解决方案：

public List<? extends Task> findTasks(TaskSearch taskSearch) {
    JPAQuery query = new JPAQuery(entityManager);

    QTask task = QTask.task;
    QInternalTask internalTask = QInternalTask.internaltask;
    BooleanBuilder where = new BooleanBuilder();

    if (taskSearch.getEmployee() != null) {
        JPASubQuery from = new JPASubQuery().from(internalTask)
                .where(internalTask.employee.eq(taskSearch.getEmployee()).and(internalTask.id.eq(task.id)));
        where.and(from.exists());
    }

    query.from(task).where(where).orderBy(task.deadline.asc());

    return query.list(task);
}

---

public list instanceOf方法不是出自JPA，是吗？尝试BooleanBuilder.getType
public List<? extends Task> findTasks(TaskSearch taskSearch) {
    JPAQuery query = new JPAQuery(entityManager);

    QTask task = QTask.task;
    QInternalTask internalTask = QInternalTask.internaltask;
    BooleanBuilder where = new BooleanBuilder();

    if (taskSearch.getEmployee() != null) {
        JPASubQuery from = new JPASubQuery().from(internalTask)
                .where(internalTask.employee.eq(taskSearch.getEmployee()).and(internalTask.id.eq(task.id)));
        where.and(from.exists());
    }

    query.from(task).where(where).orderBy(task.deadline.asc());

    return query.list(task);
}