Persisting a JSON Object using Hibernate and JPA

Question

I am trying to store a JSON object in MySQL database in spring boot. I know I am doing something wrong but I a can't figure out what it is because I am fairly new to Spring.

I have a rest endpoint where I get the following JSON object (via HTTP PUT) and I need to store it in database so that the user can fetch it later (via HTTP GET).

{
  "A": {
    "Name": "Cat",
    "Age": "1"
  },
  "B": {
    "Name": "Dog",
    "Age": "2"
  },
  "C": {
    "Name": "Horse",
    "Age": "1"
  }
}

Note that in the above case The number of keys in the object may vary, Due to that requirement I am using a HashMap to catch the object in the controller.

@RequestMapping(method = RequestMethod.POST)
    public String addPostCollection(@RequestBody HashMap<String, Animal> hp) {

        hp.forEach((x, y) -> {
            postRepository.save(hp.get(x));
        });

        return "OK";

    }

As you can see in the method, I can iterate the HashMap and persist each Animal object in db. But I am looking for a way to persist the entire HashMap in a single record. I have did some reading and they suggest me to use a @ManyToMany mapping.

Can anyone point me in a direction to persist the HashMap in a different way? (or is using the @ManyToMany the only and right way to do this?)

Answer 1

Maven dependency

The first thing you need to do is to set up the following Hibernate Types Maven dependency in your project pom.xml configuration file:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-52</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

Domain model

Let's assume you have the following entity:

@Entity(name = "Book")
@Table(name = "book")
@TypeDef(
    typeClass = JsonType.class, 
    defaultForType = JsonNode.class
)
public class Book {

    @Id
    @GeneratedValue
    private Long id;

    @NaturalId
    private String isbn;

    @Column(columnDefinition = "jsonb")
    private JsonNode properties;

    //Getters and setters omitted for brevity
}

Notice the @TypeDef is used to instruct Hibernate to map the JsonNode object using the JsonType offered by the Hibernate Types project.

Testing time

Now, if you save an entity:

Book book = new Book();
book.setIsbn( "978-9730228236" );
book.setProperties(
    JacksonUtil.toJsonNode(
        "{" +
        "   \"title\": \"High-Performance Java Persistence\"," +
        "   \"author\": \"Vlad Mihalcea\"," +
        "   \"publisher\": \"Amazon\"," +
        "   \"price\": 44.99" +
        "}"
    )
);
 
entityManager.persist( book );

Hibernate is going to generate the following SQL statement:

INSERT INTO
    book 
(
    isbn, 
    properties, 
    id
) 
VALUES
(
    '978-9730228236', 
    '{"title":"High-Performance Java Persistence","author":"Vlad Mihalcea","publisher":"Amazon","price":44.99}',  
    1
)

And you can also load it back and modify it:

Session session = entityManager.unwrap( Session.class );
 
Book book = session
    .bySimpleNaturalId( Book.class )
    .load( "978-9730228236" );
 
LOGGER.info( "Book details: {}", book.getProperties() );
 
book.setProperties(
    JacksonUtil.toJsonNode(
        "{" +
        "   \"title\": \"High-Performance Java Persistence\"," +
        "   \"author\": \"Vlad Mihalcea\"," +
        "   \"publisher\": \"Amazon\"," +
        "   \"price\": 44.99," +
        "   \"url\": \"https://www.amazon.com/High-Performance-Java-Persistence-Vlad-Mihalcea/dp/973022823X/\"" +
        "}"
    )
);

Hibernate taking caare of the UPDATE statement for you:

SELECT  b.id AS id1_0_
FROM    book b
WHERE   b.isbn = '978-9730228236'
 
SELECT  b.id AS id1_0_0_ ,
        b.isbn AS isbn2_0_0_ ,
        b.properties AS properti3_0_0_
FROM    book b
WHERE   b.id = 1
 
-- Book details: {"price":44.99,"title":"High-Performance Java Persistence","author":"Vlad Mihalcea","publisher":"Amazon"}
 
UPDATE
    book 
SET
    properties = '{"title":"High-Performance Java Persistence","author":"Vlad Mihalcea","publisher":"Amazon","price":44.99,"url":"https://www.amazon.com/High-Performance-Java-Persistence-Vlad-Mihalcea/dp/973022823X/"}'
WHERE
    id = 1