hibernate可选连接 - 需要以任何方式返回连接列值 [英] hibernate optional join - need to return join column value either way

问题描述

随后从 hibernate可选连接

系统中的许多现有查询都依赖于EntityOne和EntityTwo之间的映射关系，并且更改这不是一个附加选项，但是现在我需要开始存储和检索 tbl_one.two_id中的值不存在于连接表中。在这种情况下，这可以正常工作，如下所示：

  @Entity 
 @Table（name =tbl_one ）
 public class EntityOne 
 {
 .... 
 @ManyToOne 
 @NotFound（action = NotFoundAction.IGNORE）
 @JoinColumn（name = two_id）
私人实体两个; 
 .... 
} 
  

..但是当查询时，如果结果的值< two_id 不存在于连接表中，字段 two 的值为null，我无法告诉 tbl_one.two_id 的实际值是多少。我希望hibernate能够创建一个虚拟的 EntityTwo 对象，并且只有当关系不存在时才填充它的id字段。

我还试图将 two_id 映射到另一个没有连接的字段：

  @Entity 
 @Table（name =tbl_one）
 public class EntityOne 
 {
 .... 
 @ManyToOne 
 @NotFound（ action = NotFoundAction.IGNORE）
 @JoinColumn（name =two_id，insertable = false，updatable = false）
 private EntityTwo two; 
 
 @Column（name =two_id）
 private String twoId; 
 .... 
} 
  

...但是<$即使存在相应的记录，也不会填充c $ c> two 字段。

基本上，我需要一些插入/更新值的方法for tbl_one.two_id ，如果关系存在，或者只是<$ c的值，则检索 EntityTwo 的联合实体$ c> tbl_one.two_id 如果关系不存在。

我希望能够解决这个问题，而不需要创建两个映射同一张表。

谢谢。

编辑：更多资讯

  public class EntityTwo 
 {
 ... 
 @Id 
 @Column（name =site_id）
私人字符串ID; 
 ... 
} 
  

解决方案

这应该工作：

  @ManyToOne 
 @NotFound（action = NotFoundAction.IGNORE）
 @JoinColumn （name =two_id，insertable = false，updatable = false）
 private EntityTwo two; 
 
 @Formula（two_id）
 private String twoId; 
  

Hibernate会选择two_id列两次：一次填充两个关系，一次填充twoId 。尽管如此，twoId属性是只读的。

你也可以做相反的事情，但是它的两个属性将变为只读：

  @ManyToOne 
 @NotFound（action = NotFoundAction.IGNORE）
 @JoinFormula（two_id）
 private实体两个; 
 
 @Column（two_id）
 private String twoId; 
  

as a follow on from hibernate optional join

Many existing queries in the system rely on there being a mapped relationship between EntityOne and EntityTwo and changing this is not an attactive option, however I now need to start storing and retrieving values in tbl_one.two_id which do not exist in the joined table. On the way in, this works fine with the following mapping:

@Entity
@Table(name="tbl_one")
public class EntityOne
{
    ....
    @ManyToOne
    @NotFound(action = NotFoundAction.IGNORE)
    @JoinColumn(name = "two_id")
    private EntityTwo two;
    ....
}

.. However when querying, if a result has a value for two_id which does not exist in the joined table, the value for the field two is null and I have no way of telling what the value for tbl_one.two_id actually is. I was hoping hibernate would create a dummy EntityTwo object and populate it's id field only if the relationship did not exist.

I've also tried mapping two_id to another field without a join:

@Entity
@Table(name="tbl_one")
public class EntityOne
{
    ....
    @ManyToOne
    @NotFound(action = NotFoundAction.IGNORE)
    @JoinColumn(name = "two_id", insertable = false, updatable = false)
    private EntityTwo two;

    @Column(name = "two_id")
    private String twoId;
    ....
}

... but then the two field is never populated, even when the corresponding record exists.

Essentially I need some way of inserting/updating a value for tbl_one.two_id and retrieving a joined entity for EntityTwo if the relationship exists, or just the value for tbl_one.two_id if the relationship does not exist.

I'm hoping to be able to solve this without creating two mappings for the same table.

thanks.

EDIT: more info

public class EntityTwo
{
    ...
    @Id
    @Column(name = "site_id")
    private String id;
    ...
}

解决方案

This should work :

@ManyToOne
@NotFound(action = NotFoundAction.IGNORE)
@JoinColumn(name = "two_id", insertable = false, updatable = false)
private EntityTwo two;

@Formula("two_id")
private String twoId;

Hibernate will select the two_id column twice : once to populate the two relationship, and once to populate the twoId. The twoId property is read-only, though.

You could also do the reverse, but then it's the two property which will become read-only:

@ManyToOne
@NotFound(action = NotFoundAction.IGNORE)
@JoinFormula("two_id")
private EntityTwo two;

@Column("two_id")
private String twoId;

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