How to persist an EnumMap in Hibernate/JPA?

Question

I'm currently trying to persist data which I'd stored as a Map in Java. I've gotten this to work using List already, however when I try to make this a Map instead using @MapKeyEnumerated and @MapKey it acts a bit unexpected.

ExampleData.java

@MapKey(name = "feature")
@MapKeyEnumerated(EnumType.STRING)
@OneToMany(targetEntity = ExampleFeature.class, mappedBy = "exampleData")
private Map<Feature, ExampleFeature> features;

ExampleFeature.java

@ManyToOne
@JoinColumn(name = "example_id", nullable = false)
private ExampleData exampleData;

@Enumerated(EnumType.STRING)
@Column(name = "feature", nullable = false)
private Feature feature;

I'm able to add rows to the database manually outside of runtime, and when running the application it's able to load those entities correctly. All other entities are also working as intended.

When persisting entities in from the application, the ExampleFeature does appear in the Map , but all properties in the instance are the default Java values, and after stepping-out

Dependencies

• org.hibernate:hibernate-core:5.4.17.Final
• org.hibernate:hibernate-c3p0:5.4.17.Final

Could anyone point me in the right direction as to what I might have wrong here?

Answer 1

The issue is that in the project, #save() was only called on ExampleData , but not on any of the relational properties under it. This means that Hibernate would try to persist the ExampleData instance, however not any nested properties such as the EnumMap .

The solution is to set cascade = CascadeType.ALL which will tell Hibernate to persist changes in relational entities such as ExampleFeature when persisting ExampleData .

ExampleData.java

@MapKey(name = "feature")
@MapKeyEnumerated(EnumType.STRING)
@OneToMany(targetEntity = ExampleFeature.class, mappedBy = "exampleData", cascade = CascadeType.ALL)
private Map<Feature, ExampleFeature> features;