Hibernate如何使用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

我有一个带有复合主键的主表 A，由 两个 列组成.其中一列是constant(下面代码中的THE CONSTANT VALUE").此表定义如下所示:

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;
}

我有一个明细表 B，仅使用 一个(非常量)列引用主表 A.我想在两个表之间实现通常的 ManyToOne 和 OneToMany 关系.

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.

问题:如何使用 Hibernate 处理这种情况?

Question: How can I handle this situation with Hibernate?

我发现的主要参考的唯一解决方案依赖于使用公式:

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;
}

现在我看到其他问题:由于我之前在这里报告的 java.lang.ClassCastException 问题，我无法在 OneToMany 关系中使用此字段:https://hibernate.onjira.com/browse/HHH-6811

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

推荐答案

我真的很想知道在数据库中拥有一个常量列值会有什么帮助，但无论如何......

I really wonder how it can be helpful to have a constant column value in a database, but anyway...

我要做的就是只将非常量列映射为ID，并使常量列成为常规列，具有常量值:

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;
}

如果其他实体使用其完整的复合键引用同一 Strange 实体，则只需执行以下操作:

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;
}

您可以使用 PK 以外的其他内容引用其他实体.另一个独特的列也可以.而且由于奇怪的 ID 是独一无二的，它符合要求.在这种情况下，必须使用 referencedColumnName 属性来指定引用的列名.

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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