Hibernate如何使用一个常量作为复合外部引用的一部分 [英] Hibernate how to use a constant as part of composite foreign reference

问题描述

我有一个主表A，其中有一个由两个列组成的主键。其中一列是常量（下面代码中的常量值）。这个表的定义如下所示：

  @Entity public class Master {
 @Id 
 @Column （name =SIGNIFICANT_KEY）
 private String realKey; 
 
 @Id 
 @Column（name =CONSTANT_KEY）
 private String constantPartKey; 
 
 
 
 
 
 $ b我有一个详细表B，引用主表A只使用一个（非常量）列。我想在这两个表之间实现通常的ManyToOne和OneToMany关系。
 
 
 
 问题：Hibernate如何处理这种情况？
 
 
 
主要参考的唯一解决方案是依赖使用公式： 
 
 
  @Entity public class Detail {
 @ManyToOne 
 @JoinColumnsOrFormulas（value = {
 @JoinColumnOrFormula（column = 
 @JoinColumn（name =SIGNIFICANT_KEY， 
 referencedColumnName =SIGNIFICANT_KEY，
 insertable = false，updatable = false，nullable = false）），
 @JoinColumnOrFormula（formula = 
 @JoinFormula（referencedColumnName =CONSTANT_KEY， value ='常值'））
}）
主人主人; 
 
 
 
 
 
 $ b现在我看到另一个问题：我不能在OneToMany关系中使用这个字段，我之前在这里报告过的java.lang.ClassCastException问题： https://hibernate.onjira.com / browse / HHH-6811  
解决方案
我真的不知道如何有一个恒定的列值一个数据库，但无论如何... 
 
 
我要做的只是将非常量列映射为ID，并将常量列作为常规列，常量值：
 
 
  @Entity 
 public class Strange {
 @Id 
 private Long id ; 
 
 @Column 
 private long constant = 345; //你在数据库中想要的常量
 
 @OneToMany（mappedBy =strange）
 private Set< Detail>细节; 
 
 ... 
 //不设置常量！ 
 
 
 @Entity 
 public class Detail {
 ... 
 @ManyToOne 
 @JoinColumn（name =strange_id）
私人奇怪的; 
 
 
 
 
 
 $ b如果其他实体使用完整的组合键引用同一个陌生实体，请执行以下操作：
 
 $ $ p $ code $ @ $实际
公共类奇怪
 @ $ 
 @Column （name =strange_id）
私人长ID; 
 
 @Id 
私有长常量= 345; //你在数据库中想要的常量
 
 @OneToMany（mappedBy =strange）
 private Set< Detail>细节; 
 
 ... 
 //不设置常量！ 
} 
 
 @Entity 
 public class Detail {
 ... 
 @ManyToOne 
 @JoinColumn（name =strange_id，referencedColumnName =strange_id）
私人奇怪的; 
 
 
 
 $ b 
你可以使用除PK以外的其他实体来引用它。另一个独特的列也行。而且由于strange_id是唯一的，它符合法案。在这种情况下， referencedColumnName 属性必须用于指定被引用的列名称。
 
I have a master table A with a composite primary key, consisting of two columns. One of these columns is a constant ("THE CONSTANT VALUE" in the code below). This table definition looks like the following:
@Entity public class Master {
  @Id
  @Column(name = "SIGNIFICANT_KEY")
  private String realKey;

  @Id
  @Column(name = "CONSTANT_KEY")
  private String constantPartKey;
}
I have a detail table B, referencing master table A using only one (non-constant) column. I want to implement usual ManyToOne and OneToMany relations between the two tables.

Question: How can I handle this situation with Hibernate?

The only solution for master reference I found relies on using formulas:
@Entity public class Detail {
  @ManyToOne
  @JoinColumnsOrFormulas(value={
    @JoinColumnOrFormula(column=
      @JoinColumn(name = "SIGNIFICANT_KEY",
                  referencedColumnName = "SIGNIFICANT_KEY",
                  insertable=false, updatable=false, nullable = false)),
    @JoinColumnOrFormula(formula=
      @JoinFormula(referencedColumnName="CONSTANT_KEY", value="'THE CONSTANT VALUE'"))
  })
  Master master;
}
Now I see other problem: I cannot use this field in OneToMany relation due to the java.lang.ClassCastException problem I've reported here earlier: https://hibernate.onjira.com/browse/HHH-6811
解决方案
I really wonder how it can be helpful to have a constant column value in a database, but anyway...

What I would do is to only map the non-constant column as ID, and make the constant column a regular column, with a constant value:
@Entity
public class Strange {
    @Id
    private Long id;

    @Column
    private long constant = 345; // the constant that you want in your database

    @OneToMany(mappedBy = "strange")
    private Set<Detail> details;

    ...
    // no setter for constant!
}

@Entity
public class Detail {
   ...
   @ManyToOne
   @JoinColumn(name = "strange_id")
   private Strange strange;
}
If other entities reference this same Strange entity using its full composite key, then simply do the following:
@Entity
public class Strange {
    @Id
    @Column(name = "strange_id")
    private Long id;

    @Id
    private long constant = 345; // the constant that you want in your database

    @OneToMany(mappedBy = "strange")
    private Set<Detail> details;

    ...
    // no setter for constant!
}

@Entity
public class Detail {
   ...
   @ManyToOne
   @JoinColumn(name = "strange_id", referencedColumnName = "strange_id")
   private Strange strange;
}
You can reference other entities using something other than their PK. Another unique column is also OK. And since strange_id is unique, it fits the bill. The referencedColumnName attribute must be used to specify the referenced column name, in that case.

                        
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