JPA Criteria使用单表继承查询实体层次结构

Question

说我有以下实体:

@Entity
@Inheritance(strategy = SINGLE_TABLE)
@DiscriminatorColumn(name = "type")
public abstract class BaseEntity { 
    private Date someDate;
    private Date otherDate;
    private boolean flag;
}

@Entity
@DiscriminatorValue("entity1")
public class Entity1 extends BaseEntity { 
    private String someProperty;
}

@Entity
@DiscriminatorValue("entity2")
public class Entity2 extends BaseEntity { 
    private String otherProperty;
}

我正在尝试构建一个条件查询,该查询根据BaseEntity中的属性和两个子类返回BaseEntity实例.所以基本上我正在寻找与这个伪SQL相对应的标准查询:

SELECT * FROM <BaseEntity table name>
WHERE someDate < ? AND otherDate > ? AND flag = ?
AND someProperty = ? AND otherProperty = ?;

我宁愿不构建两个单独的查询,因为它们有很多重叠(即大多数属性都在基类中).但是,如果我将BaseEntity声明为root,我还没有想出一种在查询中引用子类属性的方法.是否可以构建这样的标准查询？

更新:

也许一些代码会澄清这个问题.我基本上喜欢做这样的事情:

CriteriaBuilder builder = ...;
CriteriaQuery<BaseEntity> query = ...;
Root<BaseEntity> root = ...;

query.select(root).where(builder.and(
        builder.lessThan(root.get(BaseEntity_.someDate), new Date()),
        builder.greaterThan(root.get(BaseEntity_.otherDate), new Date()),
        builder.isTrue(root.get(BaseEntity_.flag)),
        builder.equal(root.get(Entity1_.someProperty), "foo"),   <-- This won't work
        builder.equal(root.get(Entity2_.otherProperty), "bar")   <-- Neither will this
));

现在,我理解为什么上面的代码示例不起作用,但我想知道是否有办法解决它.

Answer 1

我设法通过将BaseEntity根目录转换为与CriteriaBuilder.treat()对应的子类类型的新根来解决这个问题,如下所示:

CriteriaBuilder builder = ...;
CriteriaQuery<BaseEntity> query = ...;
Root<BaseEntity> root = ...;
Root<Entity1> entity1 = builder.treat(root, Entity1.class);
Root<Entity2> entity2 = builder.treat(root, Entity2.class);

query.select(root).where(builder.and(
        builder.lessThan(root.get(BaseEntity_.someDate), new Date()),
        builder.greaterThan(root.get(BaseEntity_.otherDate), new Date()),
        builder.isTrue(root.get(BaseEntity_.flag)),
        builder.equal(entity1.get(Entity1_.someProperty), "foo"),
        builder.equal(entity2.get(Entity2_.otherProperty), "bar")
));