使用休眠和 3 个实体设置表

Question

I am new with Hibernate and have a question about setting up my database.

I have 3 entities: Project, R1 and R2. A Project can have one to many R1 and R1 can belong to more than 1 project. R2 belongs to a couple of Project-R1. And R2 can belong to multiple couples of Project-R1.

Examples:

My idea is to first couple Project to R1 and let Project remember which R1's it has. So a third table for joining with the Primary key of Project and R1.

When I have to couple R2 to a Project-R1 couple I was thinking of using another join table with the Primary keys of Project-R1 and R2. But how can i make the last connection using Hibernate without making a join table that has its own Primary key next to Project-R1-R2.

is it even possible?

Answer 1

Hibernate docs give this example for ternary associations:

@Entity
public class Company {
 @Id 
 int id;
 ...
 @OneToMany // unidirectional
 @MapKeyJoinColumn(name="employee_id")
 Map<Employee, Contract> contracts;
}

// or

<map name="contracts">
 <key column="employer_id" not-null="true"/>
 <map-key-many-to-many column="employee_id" class="Employee"/>
 <one-to-many class="Contract"/>
</map>

The docs also note that R2-(P+R1) type of association would typically be modeled as a separate entity class instead. It would also be my approach for this.