Hibernate OneToMany映射

Question

I have two model classes: Equity and EquityData. There is a OneToMany relationship from Equity to EquityData. I'm having a hard time getting Hibernate to bind the way I want it to.

@Entity
@Table(name="equities")
public class Equity
{
    @Id
    @GeneratedValue
    @Column(name="Equity_ID")
    private Integer id;

    private String symbol;

    @OneToMany(mappedBy="equity")
    private List<EquityData> equityData;
    ...
}


@Entity
public class EquityData 
{   
    @Id
    @GeneratedValue
    @Column(name="id")
    private Integer id;

    @ManyToOne
    @JoinColumn(name="Equity_ID")
    private Equity equity;

    @Column(name="quote_time") private Date quoteTime;
    @Column(name="quote_type_id") private Integer quoteTypeId;
    @Column(name="value") private BigDecimal value;
    ...
}

Now an Equity can have many EquityQuotes, but there will always be a "most recent" quote (the one with the latest quoteTime). Right now, the way I have Hibernate bind to my entities, it'll retrieve the Equity and all the EquityData's. I only want it to retrieve the latest EquityData for each EquityDataType (ie i dont care about yesterday's data, just today's).

In SQL, it would look like this:

select d.equity_id, d.quote_type_id, d.value, max(quote_time) 
from equities e, equity_data d
where e.equityID = d.equity_id and e.symbol = :symbol
group by d.equity_id, d.quote_type_id;

I'd appreciate any help! I don't think it matters, but I'm using this in the Stripes Web Framework.

Answer 1

You can set the fetch type as LAZY on your equity data list and then write a named query and fetch only today's equity data. Since you are using Hibernate, you can achieve this using the Criteria API as well.

Answer 2

You can set a criteria to fetch the latest quote from the database like,

Criteria crit = session.createCriteria(Equity.class);
//your criteria goes here....
crit.createCriteria(last_quoted);
List<?> entity = crit.list();
for(Iterator<?> it = equity.iterator();it.hasNext();){
Equity equity = (Equity) it.next();
//print the latest quotes based on the criteria you provided
}
session.close();
}
//catch(Exception e){ //display exeption;}

Answer 3

You can create another field to recover only the EquityData from today, adding an @Where clause to it:

@OneToMany(mappedBy = "equity")
@Where(clause = "quoteTime >= TODAY")
private List<EquityData> equityDataFromToday;

Then, you must use the field equityDataFromToday to access your data, instead of equityData (which will contain all of them)