hibernate, How to load complex object in real world

Question

a real production scenario. background: 6 tables: Fund, Account, period, periodweight, holding, position.

Fund: The fund information, for example: fund name, total Asset, start time.. etc.
Account: each fund has an account (one to one) to fund.
period:  time period ( for example: 2000-01-01 to 2000-12-31)
periodweight: at a certain period, the target holding weight.
holding:  IBM, Oracle, GE are stock holdings.
position: IBM($3000), oracle($2000), GE($5000)

if I have a fund name:fake fund, which has a target holding for IBM (30%),Oracle(20%), GE(50%) for the period(2000-01-01 to 2000-12-31), the actural position for the 2000-01-01 is 10%,10%, %80% and on 2000-01-02 is 20%,20%,60% will be represents as these records in table

Account:  id  account_Number  Fund_id
         * 1         0001        10
           2         0002        11

Fund:     id        name                    other properties...
        * 10         fake fund                     xxx
          11         another fake one              xxx

period:   id        start_time        end_time    fund_id 
         * 3        2000-01-01        2000-12-31     10
           4        2001-01-01        2001-12-31     10

periodWeight:    id      target_weight     holding_id    period_id
                *11        30%                 21           3
                *12        20%                 22           3
                *13        50%                 23           3

holding:     id             name          order       other properties... 
            *21             IBM             1              xxx
            *22             Oracle          2              xxx
            *23             GE              3              xxx

position:      id      Account_id    holding_id    date             actual_position
               1          1         11         2000-01-01          10%
               2          1         12         2000-01-01          10%
               3          1         13         2000-01-01          80%
               4          1         11         2000-01-02          20%
               5          1         12         2000-01-02          20%
               6          1         13         2000-01-02          60%

The java Class are

Account{
    @onetoOne(mappedby="account")
    Fund f;

    @oneToMany
    Set<Position> positions;
}

Fund{
    @manyToOne
    Account account;

    @oneToMany(mappedby="fund")
    Set<Period> periods;
}

Period{
    @manyToOne
    Fund fund;

    @oneToMany(mappedby="period")
    Set<PeriodWeight> periodWeights;
}

PeriodWeight{
    @manyToOne
    Period period;

    @ManyToOne
    Holding holding
}

Holding{
    @OneToMany(mappedby="holding")
    Set<PeriodWeight> periodWeights;

    @OneToMany
    Set<Position> positions;
}

Position{
    @manyToOne
    Account account;

    @manyToOne
    Holding holding;
}

I want to have a query: Based on the date (2000-01-01) and the fund name(fake fund). I want to build a Fund object, which contains the account and period(2000-01-01 to 2000-12-31), and period contains the periodWeight, and periodWeight contains holding, and holding contains postions for (2000-01-01). when there is no such position, for example, I query 2000-01-03 and fake fund, I want to have the structure, just the position is an empty set in the holding.

this hql can load the structure correctly if there is data.

select f from Fund f
inner join fetch f.account a
inner join fetch f.period p
inner join fetch p.periodWeight w
inner join fetch w.holding h
inner join fetch h.positions po
where f.name=:name and :date between p.start_date and p.end_date and :date=po.date and po.account= a

the problem is when there is no data at the position table for that day, it return null. I need a sql to give me the structure when there is no data, it can load everything except the position, just leave the position set empty.

another question is what is the better way to load such an complex structure? one hql like these or load part of the structure by one hql then other part by another hql? beause in sql, you alway load them one by one, first is the fund, then period, then weight,then holding, then position etc.. the weight need to be sort based on the holding order.

select f from Fund f
inner join fetch f.account a
inner join fetch f.period p
inner join fetch p.periodWeight w
inner join fetch w.holding h
left join fetch h.positions po with po.account= a and :date=po.date
where f.name=:name and :date between p.start_date and p.end_date

is something really close, but this give me error,

org.hibernate.hql.ast.QuerySyntaxException: with-clause not allowed on fetched associations; use filters

Answer 1

This is annoying limitation in HQL, which I have come across a few times with time based associations.

I found that this is a solution to a HQL query containing fetch and with clauses:

select f from Fund f
inner join fetch f.account a
inner join fetch f.period p
inner join fetch p.periodWeight w
inner join fetch w.holding h
left join fetch h.positions po
where f.name=:name and :date between p.start_date and p.end_date
and (po is null or (po.account= a and :date=po.date))

The trick is to move the with clause to the where clause and add an option for the object to be null allowing it to return rows with out a position.