How to Store MultivalueMap in MySQL using JPA/Hibernate

Question

I am very new to JPA/Hibernate. In my app, I am using Spring Data JPA. I have a requirement to store MultivalueMap in Mysql DB. I have found examples only based on Map, but not MultiValueMap.

At first, is that possible to store MultiValueMap in MySQL DB?

Second, I will be glad, if someone show me some good example on above.

It depends on how you want to store it. Think MultiValueMap as Map> — Eklavya, May 03 '20 at 08:09
@Eklavya I knew what is MultiValueMap , but I am not understanding how to write HIbnernate code to store that in DB, any example or sample code would be helpful for me. — john, May 03 '20 at 08:43

Eklavya · Answer 1 · 2020-05-03T10:04:16.447

You can store Map<K, List<V>> as Set<Map.Entry<K, List<V>>> this way.

@Entity
public class Entity {
    //...
    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
    @JoinColumn(name = "entity_id")
    private Set<MultiValueMapEntry> multiValueMap = new ArrayList<>();
}

@Entity
public class MultiValueMapEntry {
    private String key;

    @ElementCollection
    private List<String> values = new ArrayList<String>();
}

In Entity class use @OneToMany Unidirectional relation for every Map.Entry<K, List<V>> and use @ElementCollection for List<V> of every map entry.

To learn about @OneToMany Unidirectional see here and to learn about @ElementCollection see here

And for Set<Map.Entry<K, List<V>>> to Map<K, List<V>> converstion see here

How to Store MultivalueMap in MySQL using JPA/Hibernate

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