Question

表格：

CREATE TABLE `parent_table` (
  `parent_id` int NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`parent_id`),
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

CREATE TABLE `child_table` (
  `child_id` int NOT NULL AUTO_INCREMENT,
  `parent_id` int NOT NULL,
  PRIMARY KEY (`child_id`,`parent_id`),
  FOREIGN KEY `fk2` (`parent_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

实体类：

@Setter
@Getter
@Entity
@Table(name = "parent_table")
public class Parent implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "parent_id")
    private int parentId;
    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL,orphanRemoval = true)
    private List<Child> childs=new ArrayList<Child>();
    
    }


@Getter
@Setter
@EqualsAndHashCode
public class ChildPK implements Serializable {
    //default serial version id, required for serializable classes.
    private static final long serialVersionUID = 1L;

    @Column(name="parent_id",nullable = false) 
    private int parentId;

    @Column(name="child_id")
    private int childId;
}



@Getter
@Setter
@EqualsAndHashCode
@Entity
@IdClass(ChildPK.class)

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

    @Id
    @Column(name="child_id")
    private int childId;
     
      
    @Id
    @TableGenerator(name = "child_id_generator", table = "id_sequence", initialValue = 1, allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "child_id_generator")
    
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parent_id",insertable = false,updatable = false)
    private Parent parent;
    
    }

class MainClass{
    
    public static void main(String[] args)
    {
    entityManager.persist(parent);//in child_table parent_id storing as 0
    }
    }

在child_table parent_id列中作为外键和组合主键的一部分。

内部嵌入式类无法使用身份生成器。所以我在这里使用ID类。为child_id列生成自动增量值。

我无法将从parent_table生成的parent_id值存储为child_table作为存储为0的外键值。

有人可以检查一下映射对我有帮助吗.....

提前谢谢...

Answer 1

如果子ID已经是唯一的，为什么您需要父ID成为主键的一部分？只需使用：

@Setter
@Getter
@Entity
@Table(name = "parent_table")
public class Parent implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "parent_id")
    private int parentId;
    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL,orphanRemoval = true)
    private List<Child> childs=new ArrayList<Child>();
    
    }


@Getter
@Setter
@EqualsAndHashCode
@Entity
@Table(name = "child_table")
public class Child implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @Column(name="child_id")
    @TableGenerator(name = "child_id_generator", table = "id_sequence", initialValue = 1, allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "child_id_generator")
    private int childId;
    
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parent_id")
    private Parent parent;
    
    }

Answer 2

@Setter
@Getter
@Entity
@Table(name = "parent_table")
public class Parent implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "parent_id")
    private int parentId;
    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL,orphanRemoval = true)
    private List<Child> childs=new ArrayList<Child>();
    
    }


@Getter
@Setter
@EqualsAndHashCode
@Embeddable
public class ChildPK implements Serializable {
    //default serial version id, required for serializable classes.
    private static final long serialVersionUID = 1L;

    @Column(name="parent_id",nullable = false) 
    private int parentId;

        @TableGenerator(name = "child_id_generator", table = "id_sequence", initialValue = 1, allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "child_id_generator")
    @Column(name="child_id")
    private int childId;
}

@Getter
@Setter
@EqualsAndHashCode
@Entity
 @Table(name = "child_table")
    public class Child implements Serializable {
        private static final long serialVersionUID = 1L;

        @EmbeddableId
        private ChildPK childPk=new ChildPk(); 
   
        @ManyToOne(fetch = FetchType.LAZY)
        @MapsId("parentId")
        @JoinColumn(name = "parent_id",insertable = false,updatable = false)
        private Parent parent;
        
        }

class MainClass{
    
    public static void main(String[] args)
    {
    entityManager.persist(parent);//in child_table parent_id storing as 0
    }
    }

复合主键未映射

表格：

实体类：

2 个答案: