使用实体映射映射作为JPA中的键

Question

Is it possible to map: 是否可以映射：

@ManyToMany(cascade = Array(CascadeType.ALL), fetch = FetchType.EAGER)
Map<Entity, Double> quantities;

instead of: 代替：

Map<Double, Entity>

? ？

If not, how do you map for example Item quantities in a shop basket (without dedicated table)? 如果没有，您如何映射商店购物篮中的示例商品数量（没有专用表格）？

Thanks in advance, Etam. 在此先感谢，Etam。

Answer 1

Yes, it can be mapped without additional entity, see, for example, Hibernate: mapping many-to-many to Map . 是的，它可以在没有附加实体的情况下进行映射，例如，参见Hibernate：将多对多映射到Map 。

Also note that dedicated table will be used anyway, it just can be mapped as an entity, or not. 另请注意，无论如何都会使用专用表，它只是可以映射为实体，或者不是。

Answer 2

You can using an @ElementCollection and a @MapKeyJoinColumn, 你可以使用@ElementCollection和@MapKeyJoinColumn，

But it is kind of an unusual model, you may be better off create an Entity to map to the join table instead. 但它是一种不寻常的模型，你可能最好创建一个实体来映射到连接表。