Question

I have a noticication entity that has OneToMany relationship with its parameters, which is a list of NotificationParamEntity objects.

The code for both classes looks like:

// Notification Entity
@Entity
@Table (name = "NOTIFICATIONS")
public class NotificationEntity {
    ......
    @OneToMany (mappedBy = "notification")
    private List<NotificationParamEntity> params;
    ......
}

// Notification Parameter Entity
@Entity
@Table (name = "NOTIFICATIONS_PARAM")
public class NotificationParamEntity {
    ......
    @Column (name = "KEY", length = 40, nullable = false)
    @Enumerated (EnumType.STRING)
    private NotificationParameterEnum key;

    @Column (name = "VALUE", length = 4000, nullable = false)
    private String value;

    @ManyToOne
    @JoinColumn (name = "NOTIFICATION_ID", nullable = false)
    private NotificationEntity notification;
    ......
}

Now I can use the query below to get the notification that has a parameter named “P1” and with a value “V1”:

SELECT DISTINCT anEntity FROM NotificationEntity anEntity, IN
(anEntity.params) p WHERE p.key = “P1” AND p.value = ‘V1’

But when I want to find out the notification that has two specified parameters(P1=V1 and P2=V2), my query below failed to find anything:

SELECT DISTINCT anEntity FROM NotificationEntity anEntity, IN
(anEntity.params) p WHERE p.key = “P1” AND p.value = ‘V1’ AND p.key = “P2” AND p.value = “V2”

I can understand why it doesn’t work: there is no parameter that can have two different keys, so the query return nothing.

But how to make this work? Assume I have a notification entity that has two parameters, one is named P1 and value is V1, the other one is P2 and the value is V2, how can I find this notification entity with JPQL query?

Answer 1

Try something like this:

SELECT n FROM NotificationEntity n WHERE EXISTS 
     (SELECT p FROM NotificationParamEntity p WHERE p.key = 'P1' AND p.value = 'V1' 
     AND p.notificationEntity = n) 
AND EXISTS 
     (SELECT p2 FROM NotificationParamEntity p2 WHERE p2.key = 'P2' AND p2.value = 'V2' 
     AND p2.notificationEntity = n)

Note that it requires a reference from NotificationParamEntity to NotificationEntity (I don’t see that column in the snippet of your code, but you should have it, a @ManyToOne).