java - JPA CriteriaQuery 查询每个实体的最新数据

Question

我有一个使用 SpringBoot 1.5.9 的项目(无法更改版本)。

我有这些实体:

@Entity
@Table(name = "data")
public class DataEntity extends Timestampable {

    @Column(name = "value")
    private String value;

    @Column(name = "data_timestamp")
    private ZonedDateTime dataTimestamp;

    @ManyToOne
    @JoinColumn
    private DataTypeEntity type;

    @ManyToOne
    @JoinColumn
    private AssetEntity asset;
}

@Entity
@Table(name = "data_type")
public class DataTypeEntity extends Timestampable {

    @Column(name = "name", unique = true)
    private String name;

    ...
}

我有这个有效的 SQL 查询(在 PostgreSQL 下)，用于检索每个 Assets 的最新数据 ( source ):

SELECT * FROM data d1
JOIN (
  SELECT max(data_timestamp) as newest, asset_id FROM data
  GROUP BY asset_id
) d2
ON d1.data_timestamp = d2.newest AND d1.asset_id = d2.asset_id
WHERE d1.type_id IN (
  SELECT id FROM data_type
  WHERE name = 'ELECTRICITY_CONSUMPTION'
);

我想将此查询转换为 JPA CriteriaQuery。 有没有办法做到这一点，或者我是否需要在特定实体上使用 @SubSelect 注释？

感谢您阅读本文!

(丑陋的)解决方案

我最终使用了带有 SubSelect 的数据库 View 。 我已将 DataEntity 分成 2 个实体:

1. 操纵数据的人
2. 另一个是 View ，仅用于检索最新数据

基类:

@MappedSuperclass
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractDataEntity extends Timestampable {

    @Column(name = "value")
    protected String value;

    ...

}

操纵类:

@Entity
@SequenceGenerator(name = "idgen", sequenceName = "data_seq")
@Table(name = "data")
@DiscriminatorValue("DataEntity")
public class DataEntity extends AbstractDataEntity {
    @Override
    public DataEntity setValue(String value) {
        super.setValue(value);
        return this;
    }

   ...
}

查看类:

@Entity
@Immutable
@SequenceGenerator(name = "idgen", sequenceName = "view_data_last_seq")
@DiscriminatorValue("LastDataView")
@Subselect(
    "SELECT * FROM data d1 " +
    "JOIN ( " +
    "  SELECT max(d.data_timestamp) as newest, d.asset_id, d.type_id FROM data d " +
    "  WHERE d.parameter_id IS NULL " +
    "  GROUP BY d.asset_id, d.type_id" +
    ") d2 " +
    "ON d1.data_timestamp = d2.newest " +
    "  AND d1.asset_id = d2.asset_id " +
    "  AND d1.type_id = d2.type_id"
)
public class LastDataView extends AbstractDataEntity {
}

即使我觉得这个解决方案很丑，它也可能对其他人有帮助!

Answer 1

JPQL does not support FROM 或 JOIN 上的子查询。仅在 WHERE 或 HAVING 子句中。 Eclipse 链接，starting from 2.4 ，支持 FROM 子句上的子查询。

如every Criteria is converted to the JPQL ，不可能使用 Criteria 来完成您想要的操作。