JPA 2.0带有额外列的多对多 [英] JPA 2.0 many-to-many with extra column

问题描述

我试图在JPA 2.0（JBoss 7.1.1）中做一个ManyToMany关系，并且在关系中有一个额外的列（粗体，如下）：

I'm trying to do a ManyToMany relationship in JPA 2.0 (JBoss 7.1.1) with an extra column (in bold, below) in the relationship, like:

Employer           EmployerDeliveryAgent             DeliveryAgent
(id,...)   (employer_id, deliveryAgent_id, **ref**)  (id,...)

我不想重复属性，所以我想应用 http：// giannigar .wordpress.com / 2009/09/04 / mapping-a-many-to-many-join-table-with-extra-column-using-jpa / 。但是我无法让它工作，我得到了几个错误，如：

I wouldn't like to have duplicate attributes, so I would like to apply the second solution presented in http://giannigar.wordpress.com/2009/09/04/mapping-a-many-to-many-join-table-with-extra-column-using-jpa/ . But I can't get it to work, I get several errors like:

1. 嵌入式ID类不应包含关系映射（实际上spec中是这样说的）;
   
2. 在属性'employerDeliveryAgent'中，mapped by值'pk.deliveryAgent'不能被解析为目标实体上的属性;


3. 在属性'employerDeliveryAgent'中，映射的值'pk.employer'无法解析为目标实体上的属性;
   
4. 持续类型的覆盖属性
   
5. 无法解析持续类型的覆盖属性pk.employer;
   

1. Embedded ID class should not contain relationship mappings (in fact the spec says so);
2. In attribute 'employerDeliveryAgent', the "mapped by" value 'pk.deliveryAgent' cannot be resolved to an attribute on the target entity;
3. In attribute 'employerDeliveryAgent', the "mapped by" value 'pk.employer' cannot be resolved to an attribute on the target entity;
4. Persistent type of override attribute "pk.deliveryAgent" cannot be resolved;
5. Persistent type of override attribute "pk.employer" cannot be resolved;

$无法解析pk.deliveryAgent b $ b

该链接上的许多人都说它工作正常，所以我想我的环境中有些东西是不同的，可能是JPA或Hibernate版本。所以我的问题是：如何使用JPA 2.0（Jboss 7.1.1 /使用Hibernate作为JPA实现）来实现这种场景？为了补充这个问题：我应该避免使用组合键，而是使用纯生成的id和唯一约束吗？

Many people on that link said that it worked fine, so I suppose something is different in my environment, perhaps JPA or Hibernate version. So my question is: how do I achieve such scenario with JPA 2.0 (Jboss 7.1.1 / using Hibernate as JPA implementation)? And to complement that question: should I avoid using composite keys and instead use plain generated id and a unique constraint?

预先感谢。

Obs .:我没有在这里复制我的源代码，因为它基本上是上述链接中的一个副本，只是具有不同的类和属性名称，所以我想这不是必需的。 / p>

Obs.: I didn't copy my source code here because it is essentially a copy of the one at the link above, just with different classes and attributes names, so I guess it is not necessary.

推荐答案

首先，您需要生成 EmployerDeliveryAgentPK 类，因为它具有一个多重PK：

First of all You need to generate a EmployerDeliveryAgentPK class because It has a multiple PK:

@Embeddable
public class EmployerDeliveryAgentPK implements Serializable {

    @Column(name = "EMPLOYER_ID")
    private Long employer_id;

     @Column(name = "DELIVERY_AGENT_ID")
    private Long deliveryAgent_id;
}

接下来，您需要创建一个 EmployerDeliveryAgent class。这个类表示雇主和 DeliveryAgent 的多对多表：

Next, You need to create a EmployerDeliveryAgent class. This class represent many to many table of Employer and DeliveryAgent:

@Entity
@Table(name = " EmployerDeliveryAgent")
public class EmployerDeliveryAgent implements Serializable {

   @EmbeddedId
    private EmployerDeliveryAgentPK id;

   @ManyToOne
    @MapsId("employer_id") //This is the name of attr in EmployerDeliveryAgentPK class
    @JoinColumn(name = "EMPLOYER_ID")
    private Employer employer;

    @ManyToOne
    @MapsId("deliveryAgent_id")
    @JoinColumn(name = "DELIVERY_AGENT_ID")
    private DeliveryAgent deliveryAgent;    
}

之后，在雇主



After that, in Employer class You need to add:

@OneToMany(mappedBy = "deliveryAgent")
    private Set<EmployerDeliveryAgent> employerDeliveryAgent = new HashSet<EmployerDeliveryAgent>();

并且在 DeliveryAgent 类中您需要添加：

And in DeliveryAgent class You need to add:

@OneToMany(mappedBy = "employer")
        private Set<EmployerDeliveryAgent> employer = new HashSet<EmployerDeliveryAgent>();

这就是全部！祝你好运!!

This is all! Good luck!!

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