Hibernate：将多对多映射到Map [英] Hibernate: mapping many-to-many to Map

问题描述

我正在开发一个涉及以下两个实体的应用程序：产品（我们将其命名为X，Y，Z）和材料（a，b，c， ...）。众所周知，每个产品都有一个配方，表明制造这种产品需要什么材料。例如，为了生成一个X，我们需要2 a，6 c和4 d（X = 2a + 6c + 4d）。

I am developing an application which deals with two following entities: Products (let's name it as X, Y, Z) and Materials (a, b, c, ...). It's known that every product has a recipe which indicates what materials are required for making this product. For example, to produce one X we need 2 a, 6 c and 4 d (X = 2a + 6c + 4d).

这是它在数据库表中的反映：

That's how it reflects in a database tables:

Products
id INT
name VARCHAR
...

Materials
id INT
name VARCHAR
...

Recipes
product_id INT
material_id INT
count INT

第三个表中的计数字段是同类材料的系数（2， 6，4从示例）。

The "count" field in the third table is a coefficient for materials of the same kind (2, 6, 4 from the example).

所以我想以这种方式组合产品类：

So I want to compose Product class this way:

public class Product {
    ...
    private Map<Material, Integer> recipe; // How many units of each material we need?
    ...
}

是一种获取所有必要的方法食谱数据使用Hibernate映射？

Is it a way to fetch all the necessary data for recipe Map using Hibernate? The separate configuration approach (without annotations) is preferred.

推荐答案

由于没有人发布解决方案而没有注释，我会显示解决方案与JPA 2.0 @ElementCollection 注释：

Since nobody posted the solution without annotations, I'll show the solution with JPA 2.0 @ElementCollection annotation:

@ElementCollection
@CollectionTable(name = "Recipes", 
    joinColumns = @JoinColumn(name = "product_id"))
@MapKeyJoinColumn(name = "material_id")
@Column(name = "count")
private Map<Material, Integer> recipe;

另请注意，由于您的地图的类的值为整数，没有注释的解决方案可能被记录为集合映射而不是实体关系映射。

Also note that since class of values of your map is Integer, solution without annotations is likely to be documented as "collection mapping" rather than "entity relationship mapping".

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