java - JPA 多对一在引用表中具有常量值

Question

我正在做 Spring Boot 项目并使用 spring-boot-jpa(Hibernate 实现)。我在配置实体之间的以下关系时遇到问题。

假设我需要两个表之间的多对一(以及相反的一对多)关系(本例中的 MySQL，table1 在逻辑上存储各种其他表中代码的描述):

CREATE TABLE `table1` (
   `id` INT NOT NULL AUTO_INCREMENT,
   `ref_table` VARCHAR(50) NOT NULL,
   `ref_column` VARCHAR(50) NOT NULL,
   `code` VARCHAR(10) NOT NULL,
   `description` VARCHAR(100) NOT NULL,
   PRIMARY KEY (`id`),
   UNIQUE INDEX `u_composite1` (`ref_table` ASC, `ref_column` ASC, `code` ASC));

CREATE TABLE `table2` (
   `id` INT NOT NULL AUTO_INCREMENT,
   `field1` VARCHAR(100) NULL,
   `code` VARCHAR(10) NOT NULL,
   PRIMARY KEY (`id`));

我在SQL中连接这两个表的方式是这样的:

SELECT t2.*, t1.description 
FROM table2 t2 
JOIN table1 t1 
  ON    ( t1.ref_table = 'table2'
      AND t1.ref_column = 'code' 
      AND t1.code = t2.code);

所以，我创建了这样的实体(减去了 getter 和 setter):

@Entity
@Table(name = "table1")
public class Table1  implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(unique = true, nullable = false)
    private int id;

    @Column(nullable = false, length = 10)
    private String code;

    @Column(length = 100)
    private String description;

    @Column(name = "ref_column", nullable = false, length = 50)
    private String refColumn;

    @Column(name = "ref_table", nullable = false, length = 50)
    private String refTable;

    @OneToMany(mappedBy = "table1")
    private List<Table2> table2;
}

@Entity
@Table(name = "table2")
public class Table2  implements Serializable {
    private static final long serialVersionUID = 1L;

   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column(unique = true, nullable = false)
   private int id;

   @Column(nullable = false, length = 45)
   private String field1;

   @ManyToOne(fetch=FetchType.LAZY)
   @Column(name = "code")
   @JoinColumns({
      @JoinColumn(name = "code", referencedColumnName = "code", nullable = false, updatable = false),
      @JoinColumn(name = "'table2'", referencedColumnName = "ref_table", nullable = false, updatable = false),
      @JoinColumn(name = "'code'", referencedColumnName = "ref_column", nullable = false, updatable = false)
   })
   private Table1 table1;

}

但它不起作用。 :(

这种关系甚至可以在 JPA 中定义吗？ 如果是，请问如何？

Answer 1

关于“使用常量值连接”问题，我设法使用@Where Hibernate 注释使其工作:

• How to replace a @JoinColumn with a hardcoded value?

  @Entity
  @Table(name = "a")
  public class A {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      public long id;
  
      @OneToMany
      @JoinColumn(name = "id", referencedColumnName = "id")
      @Where(clause = "blah = 'CONSTANT_VALUE'")
      public Set<B> b;
  
      protected A() {}
  }
  
  @Entity
  @Table(name = "b")
  public class B {
      @Id
      @Column(nullable = false)
      public Long id;
  
      @Column(nullable = false)
      public String blah;
  
      protected B() {}
  }