Persist a collection of data to a lazy collection in Spring Framework

Question

I'm newbie in Spring. The picture above shows my db schema:

I need to download a new real time data for each station each minute and I have to assign it to that station. I would like to manage to:

1. persist
2. without the use of FetchType.EAGER (which resulted to be too much slow for this purpose)
3. persist in a single time (i.e a single communication with db, without iterating on a list the persist function on each single RealTimeData) the collection of RealTimeData collected in the previous minute.

This is what I would like to do, if I should take a completely different way for doing something like that any advice is appreciated.

The station class is this:

@RooJavaBean
@RooToString
@RooJpaActiveRecord(finders = { "findStationsByNum" })
@RooJson
public class Station {

    private String address;
    private String name;
    private Integer num;
    @ManyToOne(cascade = CascadeType.ALL)
    private Location location;
    @ManyToOne
    private City city;
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "station", fetch=FetchType.LAZY)
    private Set<RealTimeData> real_time_data = new HashSet<RealTimeData>();

}

And the RealTimeData class is this:

@RooJavaBean
@RooToString
@RooJpaActiveRecord(finders = { "findRealTimeDatasByCollect_dateEquals" })
@RooJson
public class RealTimeData {

    private Integer available_bike_stands;
    /* ... ... ... */
    @Temporal(TemporalType.TIMESTAMP)
    @DateTimeFormat(style = "M-")
    private Date collect_date;
    @ManyToOne
    private Station station;
}

Answer 1

You can read the details of the solution here: http://forum.spring.io/forum/spring-projects/roo/106714-bulk-operations-with-spring-roo

However synthesizing it suggests to use this:

@PersistenceContext
private EntityManager entityManager;

@Transactional
public void storeList(List<MyEntity> entities) {
  int imported = 0;
  for (MyEntity e: entities) {
    entityManager.persist(e);
    if (++imported % 50 == 0) {
      entityManager.flush();
      entityManager.clear();
    }
  }
}

Or if you are using Spring Roo this:

@Transactional
public void storeList(List<MyEntity> entities) {
    int imported = 0;
    for (MyEntity e: entities) {
        e.persist();
        if (++imported % 50 == 0) {
            e.flush();
            e.clear();
        }
    }
}

Setting in the property of your persistence.xml:

<property name="hibernate.jdbc.batch_size" value="50"/>