JPA - @OneToMany as a Map

In my case, it is worked with @OneToMany(cascade=CascadeType.PERSIST) @MapKeyColumn(name="COLUMN_NAME")

or

You can directly try with only @OneToMany(cascade=CascadeType.PERSIST)

Try using @MapKey(name = "locale") instead.

@MapKeyJoinColumn is used when your map key is an entity, but here you're just using the locale String.