Hibernate custom query on Maps generates unwanted subqueries

Question

I have a class Purchase with a map inside.

@Entity
public class Purchase {

    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    private Integer purchaseId;

    @ManyToOne
    @JoinColumn(name = "customer_id")
    private User customer;

    @ManyToOne
    @JoinColumn(name = "item_id")
    private Item item;

    private String customization;

    @ElementCollection
    @MapKeyEnumerated(value = EnumType.STRING)
    @CollectionTable(name = "purchase_status")
    @MapKeyColumn(name = "status")
    @Column(name = "date")
    private Map<PurchaseStatus, Date> statusTransitions = new HashMap<>();

    private Date expectedDeliveryDate;

    @ManyToOne
    @JoinColumn(name = "purchase_cart_id")
    @JsonIgnore
    private PurchaseCart purchaseCart;

    @OneToOne
    @JoinColumn(name = "destination_address_id")
    private DestinationAddress destinationAddress;

    @Transient
    @JsonIgnore
    private Date purchaseDate;

It represent a purchase. PurchaseStatus is an enumerator. statusTransitions represents all the status this purchase got. In particular it can be 'READY_TO_BE_PAID' and 'PAID'. The status has it relative date, which is the VALUE of the map, and the status itself is the KEY of the map just because a purchase can be in a precise status only once. I would like to get from the database all the Purchases with a specific User (username, which is an attribute of User) and with a specific (KEY, VALUE) pair inside the statusTransitions HashMap. In particular I would like to create a query which returns all the purchases where the Date (VALUE) is between two dates (fromDate and toDate) and the PurchaseStatus (KEY) is equal to the enum value 'READY_TO_BE_PAID'.

I created this custom query:

@Query("select p from Purchase p JOIN p.customer c JOIN p.statusTransitions s WHERE c.username = :username and " +
            "(KEY(s) = 'READY_TO_BE_PAID' and " +
            "VALUE(s) >= :fromDate and " +
            "VALUE(s) <= :toDate)")
List<Purchase> findByUsernameAndByDate(@Param("fromDate") Date fromDate, @Param("toDate") Date toDate, @Param("username") String username);

The only problem is that the SQL query that generates is the following:

select 
*
from 
  purchase purchase0_ 
    inner join user user1_ on purchase0_.customer_id=user1_.user_id 
    inner join purchase_status statustran2_ on purchase0_.purchase_id=statustran2_.purchase_purchase_id 
  where 
    statustran2_.status='READY_TO_BE_PAID' and 
    user1_.username=? and 
      (select 
        statustran2_.date 
      from 
        purchase_status statustran2_ 
      where 
        purchase0_.purchase_id=statustran2_.purchase_purchase_id
        )>=? and 
      (select 
        statustran2_.date 
      from 
        purchase_status statustran2_ 
      where 
        purchase0_.purchase_id=statustran2_.purchase_purchase_id
      )<=?

Which is not what I want. It generates two subqueries and the result is that it throws this error:

java.sql.SQLException: Subquery returns more than 1 row

That's because when it executes the subquery it doesn't filter the rows on the PurchaseStatus, returning in that way more than one row. The point is that I don't know how to rewrite the query in order to avoid these two subqueries or to put inside the WHERE clause this (KEY(s) = 'READY_TO_BE_PAID') condition. I found other people which have had the same issue but I couldn't find any solution.

Answer 1

I found the solution! It seems that when you have this query

SELECT p 
FROM Purchase p 
    JOIN p.customer c 
    JOIN p.statusTransitions s

the alias 's' of the statusTransactions Map, is already the value and not the pair (KEY, VALUE) which you are led to believe. It's a bit counter intuitive because KEY returns the key but VALUE does not return the value, but instead it generates automatically a subquery which inevitably leads you to errors.

java.sql.SQLException: Subquery returns more than 1 row

So the correct way to rewrite this:

SELECT p 
FROM Purchase p 
    JOIN p.customer c 
    JOIN p.statusTransitions s 
WHERE 
    c.username = :username and
    KEY(s) = 'READY_TO_BE_PAID' and
    VALUE(s) >= :fromDate and
    VALUE(s) <= :toDate

is:

SELECT p 
FROM Purchase p 
    JOIN p.customer c 
    JOIN p.statusTransitions s 
WHERE 
    c.username = :username and
    KEY(s) = 'READY_TO_BE_PAID' and
    s >= :fromDate and
    s <= :toDate

or more compactly:

SELECT p 
FROM Purchase p 
    JOIN p.customer c 
    JOIN p.statusTransitions s 
WHERE 
    c.username = :username and
    KEY(s) = 'READY_TO_BE_PAID' and
    s BETWEEN :fromDate and :toDate

where, as I already said, the alias 's' is already the value of the (key,value) pair!