Introduction

The open-source Hypersistence Utils project allows you to map Java objects or Jackson JsonNode as JPA or Hibernate entity properties, and, thanks to our awesome contributors, we have added support for storing type-safe JSON collections.

In this article, you are going to see how to achieve this goal.

Maven dependency

First of all, you need to set up the following Maven dependency in your project pom.xml configuration file:

<dependency>
    <groupId>io.hypersistence</groupId>
    <artifactId>hypersistence-utils-hibernate-55</artifactId>
    <version>${hypersistence-utils.version}</version>
</dependency>

If you’re using older versions of Hibernate, check out the Hypersistence Utils GitHub repository for more info about the matching dependency for your current Hibernate version.

Domain Model

Let’s assume we have the following Location Java object type.

public class Location implements Serializable {

    private String country;

    private String city;

    //Getters and setters omitted for brevity

    @Override
    public String toString() {
        return "Location{" +
                "country='" + country + ''' +
                ", city='" + city + ''' +
                '}';
    }
}

And one Event entity that is mapped as follows.

For Hibernate 6, the mapping will look as follows:

@Entity(name = "Event")
@Table(name = "event")
public class Event extends BaseEntity {

    @Type(JsonType.class)
    @Column(columnDefinition = "jsonb")
    private Location location;

    @Type(JsonType.class)
    @Column(columnDefinition = "jsonb")
    private List<Location> alternativeLocations = new ArrayList<Location>();

    //Getters and setters omitted for brevity
}

And for Hibernate 5, like this:

@Entity(name = "Event")
@Table(name = "event")
@TypeDef(name = "json", typeClass = JsonType.class)
public class Event extends BaseEntity {

    @Type(type = "json")
    @Column(columnDefinition = "jsonb")
    private Location location;

    @Type(type = "json")
    @Column(columnDefinition = "jsonb")
    private List<Location> alternativeLocations = new ArrayList<Location>();

    //Getters and setters omitted for brevity
}

That’s it!

Testing time

When saving the following Event entity:

Location cluj = new Location();
cluj.setCountry("Romania");
cluj.setCity("Cluj-Napoca");

Location newYork = new Location();
newYork.setCountry("US");
newYork.setCity("New-York");

Location london = new Location();
london.setCountry("UK");
london.setCity("London");

Event event = new Event();
event.setId(1L);
event.setLocation(cluj);
event.setAlternativeLocations(
    Arrays.asList(newYork, london)
);

entityManager.persist(event);

Hibernate will generate the following SQL INSERT statement:

INSERT INTO event (
    version, 
    alternativeLocations, 
    location, 
    id
) 
VALUES (
    0, 
    [
        {"country":"US","city":"New-York"},
        {"country":"UK","city":"London"}
    ], 
    {"country":"Romania","city":"Cluj-Napoca"}, 
    1
)

Also, when retrieving back the Event entity, both the location and thealternativeLocations` properties are properly fetched:

Event event = entityManager.find(Event.class, eventId);

assertEquals(
    "Cluj-Napoca", 
    event.getLocation().getCity()
);

assertEquals(2, event.getAlternativeLocations().size());

assertEquals(
    "New-York", 
    event.getAlternativeLocations().get(0).getCity()
);
assertEquals(
    "London", 
    event.getAlternativeLocations().get(1).getCity()
);

Cool, right?

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Conclusion

The Hypersistence Utils project supports more than JSON types. You can map PostgreSQL ARRAY types or PostgreSQL-specific Enums, nullable Character, or even provide your own custom immutable Hibernate Types.

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