How to map JSON objects using generic Hibernate Types
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Introduction
In this article, we are going to see how you can map a JSON column to a JPA entity attribute using the Hypersistence Utils open-source project.
While you can create your own custom Hibernate Types, for mapping JSON column types on Oracle, SQL Server, PostgreSQL, or MySQL, you don’t need to implement your own Hibernate Type since the Hypersistence Utils project already offers this functionality.
The Domain Model
Assuming we have the following Domain Model:
Location
and Ticket
are JSON Object(s)
, while Event
and Participant
are JPA entities. Our goal is to provide a Hibernate JSON Type
that works for any type of JSON Java Object
and on any relational database that supports JSON columns.
Maven dependency
The first thing you need to do is 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>
Declaring the Hypersistence Utils
For Hibernate 6, you can use the @Type
annotation when mapping an entity attribute on a JSON column:
@Type(JsonType.class) private Map<String, String> properties = new HashMap<>();
For Hibernate 5, you can use the @TypeDef
annotation to make use of the JSON Hibernate Types:
@TypeDef(name = "json", typeClass = JsonType.class) @MappedSuperclass public class BaseEntity { //Code omitted for brevity }
The
@TypeDef
annotations can be applied to a base entity class or in thepackage-info.java
file associated with your current entity’s package.
MySQL
MySQL 5.7 added support for JSON types, which, at the JDBC level, need to be materialized as String
. However, the JsonType
is smart knows how to handle each DB, so there’s nothing to worry about.
The entity mapping looks like this:
@Entity(name = "Event") @Table(name = "event") public class Event extends BaseEntity { @Type(type = "json") @Column(columnDefinition = "json") private Location location; public Location getLocation() { return location; } public void setLocation(Location location) { this.location = location; } } @Entity(name = "Participant") @Table(name = "participant") public class Participant extends BaseEntity { @Type(type = "json") @Column(columnDefinition = "json") private Ticket ticket; @ManyToOne private Event event; public Ticket getTicket() { return ticket; } public void setTicket(Ticket ticket) { this.ticket = ticket; } public Event getEvent() { return event; } public void setEvent(Event event) { this.event = event; } }
When inserting the following entities:
final AtomicReference<Event> eventHolder = new AtomicReference<>(); final AtomicReference<Participant> participantHolder = new AtomicReference<>(); doInJPA(entityManager -> { Event nullEvent = new Event(); nullEvent.setId(0L); entityManager.persist(nullEvent); Location location = new Location(); location.setCountry("Romania"); location.setCity("Cluj-Napoca"); Event event = new Event(); event.setId(1L); event.setLocation(location); entityManager.persist(event); Ticket ticket = new Ticket(); ticket.setPrice(12.34d); ticket.setRegistrationCode("ABC123"); Participant participant = new Participant(); participant.setId(1L); participant.setTicket(ticket); participant.setEvent(event); entityManager.persist(participant); eventHolder.set(event); participantHolder.set(participant); });
Hibernate generates the following statements:
INSERT INTO event (location, id) VALUES (NULL(OTHER), 0) INSERT INTO event (location, id) VALUES ('{"country":"Romania","city":"Cluj-Napoca"}', 1) INSERT INTO participant (event_id, ticket, id) VALUES (1, {"registrationCode":"ABC123","price":12.34}, 1)
The JSON Object(s)
are properly materialized into their associated database columns.
Not only that JSON Object(s)
are properly transformed from their database representation:
Event event = entityManager.find(Event.class, eventHolder.get().getId()); assertEquals("Cluj-Napoca", event.getLocation().getCity()); Participant participant = entityManager.find( Participant.class, participantHolder.get().getId() ); assertEquals("ABC123", participant.getTicket().getRegistrationCode());
But we can even issue native JSON-based SQL queries:
List<String> participants = entityManager.createNativeQuery(""" SELECT p.ticket -> \"$.registrationCode\" FROM participant p WHERE JSON_EXTRACT(p.ticket, \"$.price\") > 1 """) .getResultList();
And JSON Object(s)
can be modified:
event.getLocation().setCity("Constanța"); entityManager.flush();
Hibernate generating the proper UPDATE statement:
UPDATE event SET location = '{"country":"Romania","city":"Constanța"}' WHERE id = 1
PostgreSQL
PostgreSQL has been supporting JSON types since version 9.2. There are two types that can be used:
json
jsonb
Both PostgreSQL JSON types need to be materialized using a binary data format, but the generic JsonType
can handle this just fine.
PostgreSQL JSON column type
For the JSON
column type, the two JSON Object(s)
mapping must be changed as follows:
@Type(type = "json") @Column(columnDefinition = "json") private Location location; @Type(type = "json") @Column(columnDefinition = "json") private Ticket ticket;
The insert works just the same, as well as the entity update, and we can even query the JSON
column as follows:
List<String> participants = entityManager.createNativeQuery(""" SELECT p.ticket ->>'registrationCode' FROM participant p WHERE p.ticket ->> 'price' > '10' """) .getResultList();
PostgreSQL JSONB column type
For the JSONB
column type, we only need to change the columnDefinition
attribute since both the json
and jsonb
PostgreSQL column types are handled by the JsonType
:
@Type(type = "json") @Column(columnDefinition = "jsonb") private Location location; @Type(type = "json") @Column(columnDefinition = "jsonb") private Ticket ticket;
The insert and the JSON Object
update work the same, while the JSONB column type provides more advanced querying capabilities:
List<String> participants = entityManager.createNativeQuery(""" SELECT jsonb_pretty(p.ticket) FROM participant p WHERE p.ticket ->> 'price' > '10' """) .getResultList();
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Conclusion
The Hypersistence Utils support for JSON column mapping is very useful, and you can use it to map entity attributes that are either POJO, String
, or even JsonNode
.
The best thing about the Hypersistence Utils project is that it offers support for Oracle, SQL Server, PostgreSQL, or MySQL JSON column types.
