@Entity(name = "MapContainer")
    @Table(name = "map_container")
    public static class MapContainer {
        @Id
        private Long id;
        @ManyToMany
        @MapKey(name = "mapKey")
        private Map<MapKeyEntity, MapValueEntity> map = new HashMap<>();

        public MapContainer() { }

        public MapContainer(Long id) {
            this.id = id;
        }
    }

    @Entity(name = "MapKeyEntity")
    @Table(name = "map_key_entity")
    public static class MapKeyEntity {
        @Id
        private Long id;

        public MapKeyEntity() { }

        public MapKeyEntity(Long id) {
            this.id = id;
        }
    }

    @Entity(name = "MapValueEntity")
    @Table(name = "map_value_entity")
    public static class MapValueEntity {
        @Id
        private Long id;
        @ManyToOne(optional = false)
        private MapContainer mapContainer;
        @ManyToOne(optional = false)
        @JoinColumn(unique = true)
        private MapKeyEntity mapKey;

        public MapValueEntity() { }

        public MapValueEntity(Long id) {
            this.id = id;
        }
    }