selecting existing and non existing joined entity at once - jpa

Question

I have a join table looks like this.
EXCHANGE_RATE
------------------------------
ID BIGINT PK
SOURCE_CURRENCY_ID BIGINT FK
TARGET_CURRENCY_ID BIGINT FK
Mapped ExchangeRate.java
public class ExchangeRate {
protected ExchangeRage() {
this(null, null);
}
// for SELECT NEW
public ExchangeRate(Currency sourceCurrency, Currency targetCurrency) {
this.sourceCurrency = sourceCurrency;
this.targetCurrency = targetCurrency;
}
#Id private Long id;
#ManyToOne private Currency sourceCurrency;
#ManyToOne private Currency targetCurrency;
}
How can I list all existing and non existing ExchangeRates for given sourceCurrency?
For example,
There are three Currencies. A, B, and C.
There is already an ExhangeRate from A to B
With following method, if sourceCurrency is A,
public List<ExchangeRate> listExchangeable(Currency sourceCurrency) {
//
}
How can I get following list?
ExchangeRate {
id: 0
sourceCurrency: A
targetCurrency: B
},
ExchangeRate {
id: NULL
sourceCurrency: A
targetCurrency: C
}

Answer 1

Required Query
// get all exchange rates for a source currency
public List<ExchangeRate> listExchangeable(Currency sourceCurrency) {
Query qry = em.createQuery("select r from ExchangeRate r where
r.sourceCurrency = :sourceCurrency");
qry.setParameter("sourceCurrency", sourceCurrency);
return qry.getResultList();
}
for non existing ExchangeRates for given sourceCurrency
Query qry = em.createQuery("select r from ExchangeRate r where
r.sourceCurrency != :sourceCurrency");