How to use a child association property as a Map key in JPA parent entity

Question

I\'m having two entities Car and CarDescription where CarDescription is depending on another foreign key from the table Language

Answer 1

In CarDescription you need to add the languageId property:

@Column(name = "language_id", insertable = false, updatable = false)
private Long languageId;

@NotNull
@OneToOne
@JoinColumn(name = "language_id")
private Language language;

public void setLanguage(Language language) {
    this.languageId = language.getId();
    this.language = language;
} 

Then you can use it in the Car entity like this:

@OneToMany(mappedBy="car")
@MapKey(name = "languageId")
private Map<Long, CarDescription> carDescription = new HashMap<>(0);