如何通过ID加入实体(How to join entity by id)

 你能帮我解决一个小问题吗？ 这是关于Spring Data，JPA和Hibernate的项目。 
 
 我有两个实体，我需要一个到另一个。 是的，这听起来很简单:) 
 
 首先是活动： 
 
public class Activity {
  ...

  @Column(name="STATUS_ID")
  private String statusId;

  ...
}
 
 其次是Vocab值（用户可以将它作为一个简单的值列表）： 
 
public class VocabValue {
  ...

  // Type of vocab (in our case - 'ACT_STAT')
  @Column(name="TYPE")
  private String type;

  // Name - code of Vocab value
  @Column(name="NAME")
  private String type;

  // Value
  @Column(name="VAL")
  private String value;

  ...
}
 
 在我的情况下，我想在一个活动中存储一个Vocab值的名称并加入它。 
 
 在目标状态下，我的实体应该如下所示： 
 
public class Activity {
  ...

  @Column(name="STATUS_ID")
  private String statusId;

  @... what?
  private String status;

  // Getter returns Vocab Value in accordance with the following join spec (pseudo-sql):
  // select voc.value from VocabValue voc where voc.name = %statusId% and type = 'ACT_STAT'
  public String getStatus() {
  }

  ...
}
 
 我应该如何配置我的活动实体来提供这个？ 好的，这可能吗？ 
 
 我会很感激你的建议！ 
 
 谢谢！ 
 
 更新13.01 
 
 我试过这个解决方案： 
 
public class Activity {

  ...
  @Column(name="STATUS_ID")
  private String statusId;

  @JoinColumn(name = "STATUS_ID", referencedColumnName = "NAME",   insertable = false, updatable = false)
  @Where(clause = "type = 'ACT_STAT'")
  @ManyToOne(optional = true)
  @NotFound(action = NotFoundAction.IGNORE)
  private VocabValue status;

  ...
}
 
 此外，我必须使VocabValue实现Serializable（VocabValue作为Detached实体应该按照Hibernate规范的Serializable接口的实现）。 
 
public VocabValue implemets Serializable {...}
 
 它可以工作，但注解@Where不起作用：仅使用@JoinColumn规范执行联接，在@Where子句中定义的附加条件不适用。 
 
 是否有解决方法？ 
 
 更新13.01 - 2 
 
 它通过以下配置解决： 
 
@JoinFormula(value="SELECT v.ROW_ID FROM VOCAB v WHERE v.NAME=STATUS_ID AND v.TYPE='ACT_STAT'") 
@ManyToOne 
@NotFound(action = NotFoundAction.IGNORE) 
private VocabValue status;
 
 谢谢！） 

Could you help me solve a small question? It's about the project with Spring Data, JPA and Hibernate.
 
I have 2 entities and I need to join one to another. Yes, it sounds simple :)
 
First is Activity:
 
public class Activity {
  ...

  @Column(name="STATUS_ID")
  private String statusId;

  ...
}
 
Second is Vocab Value (Users can administer it as a simple list of values):
 
public class VocabValue {
  ...

  // Type of vocab (in our case - 'ACT_STAT')
  @Column(name="TYPE")
  private String type;

  // Name - code of Vocab value
  @Column(name="NAME")
  private String type;

  // Value
  @Column(name="VAL")
  private String value;

  ...
}
 
In my case, I want to store in an Activity a name of Vocab Value and join it. 
 
In the target state, my entity should look like:
 
public class Activity {
  ...

  @Column(name="STATUS_ID")
  private String statusId;

  @... what?
  private String status;

  // Getter returns Vocab Value in accordance with the following join spec (pseudo-sql):
  // select voc.value from VocabValue voc where voc.name = %statusId% and type = 'ACT_STAT'
  public String getStatus() {
  }

  ...
}
 
How should I configure my Activity entity to provide this? Ok, Is it possible?
 
I'll be grateful for your advice!
 
Thank!
 
Update 13.01
 
I've tried this solution:
 
public class Activity {

  ...
  @Column(name="STATUS_ID")
  private String statusId;

  @JoinColumn(name = "STATUS_ID", referencedColumnName = "NAME",   insertable = false, updatable = false)
  @Where(clause = "type = 'ACT_STAT'")
  @ManyToOne(optional = true)
  @NotFound(action = NotFoundAction.IGNORE)
  private VocabValue status;

  ...
}
 
Moreover, I had to make VocabValue implementation of Serializable (VocabValue as Detached entity should be implemetation of Serializable interface in accordance with Hibernate spec).
 
public VocabValue implemets Serializable {...}
 
It works, but annotation @Where doesn't work: Join performed only with @JoinColumn specification, an additional criteria, defined in @Where clause doesn't apply.
 
Whether there are workarounds? 
 
UPDATE 13.01 - 2
 
It was solved with following configuration:
 
@JoinFormula(value="SELECT v.ROW_ID FROM VOCAB v WHERE v.NAME=STATUS_ID AND v.TYPE='ACT_STAT'") 
@ManyToOne 
@NotFound(action = NotFoundAction.IGNORE) 
private VocabValue status;
 
Thanks!)

原文：https://stackoverflow.com/questions/41624890