I have a project that uses SpringBoot 1.5.9 (can't change version).
I have these entities :
@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;
...
}
I have this working SQL query (under PostgreSQL), to retrieve the latest data per asset (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'
);
I want to translate this query into a JPA CriteriaQuery. Is there a way to do so, or do I need to use a @SubSelect annotation on a specific entity ?
Thanks for reading this !
(UGLY) SOLUTION
I ended up using a database View, with a SubSelect. I've split my DataEntity into 2 entities :
- One to manipulate the datas
- Anoher that is a view and used only to retrieve the latest data
Base class :
@MappedSuperclass
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractDataEntity extends Timestampable {
@Column(name = "value")
protected String value;
...
}
Manipulation class :
@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;
}
...
}
View class :
@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 {
}
Even if I find this solution ugly, it may help others !
