java - 在 Spring Data JPA 中保留两个不同模式之间具有父子关系的表

Question

我正在努力，

ChildTable child = new ChildTable();
clild.setParentTwoID(prentTwoID);
ParentOne parentOne = new ParentOne();
parentOne.getChildTableList().add(childTable);
parentReposetory.save(parentOne);

其中，ParentOne 在 schema S1 中，而 ParentTwo 和 ChildTable 在 schema S2 中。

ParentOne.java

@Data
@EqualsAndHashCode(callSuper = false)
@Entity
@Table(name = "ParentOne", schema = "S1")
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class, scope = ParentOne.class)
public class ParentOne implements Serializable {

    private static final long serialVersionUID = 7502273069461829133L;

    @Id
    @Column(name = "ParentOneID", unique = true, nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer parentOneID;

    @OneToMany(targetEntity = ChildTable.class, fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "ParentOneID", nullable = false, insertable = false, updatable = false)
    private List<ChildTable> childTableList;
}

ParentTwo.java

@Data
@EqualsAndHashCode(callSuper = false)
@Entity
@Table(name = "ParentTwo", schema = "S2")
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class, scope = ParentTwo.class)
public class ParentTwo implements Serializable {

    private static final long serialVersionUID = 7502273069461829133L;

    @Id
    @Column(name = "ParentTwoID", unique = true, nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer parentTwoID;

    @OneToMany(targetEntity = ChildTable.class, fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "ParentTwoID", nullable = false, insertable = false, updatable = false)
    private List<ChildTable> childTableList;
}

ChildTable.java

@Data
@EqualsAndHashCode(callSuper = false)
@Entity
@Table(name = "ChildTable", schema = "S2")
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class, scope = ChildTable.class)
public class ChildTable implements Serializable {

    private static final long serialVersionUID = -6331600489988183852L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "ChildTableID", unique = true, nullable = false)
    private Integer childTableID;

    @Column(name = "ParentOneID")
    private Integer parentOneID;

    @Column(name = "ParentTwoID", nullable = false)
    @NotNull(message = "mandatory_field")
    private Integer parentTwoID;

}

这里 ParentTwo 已经存在并且我有它的 Id。我将只保留 ParentOne 以及不同架构的 ChildTable。当我这样做时，我会收到错误提示。

rg.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement

Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: Cannot insert the value NULL into column 'ParentOneID', table 'PT_Sample.S2.ChildTable'; column does not allow nulls. INSERT fails.

SQL Error: 515, SQLState: 23000

Answer 1

使用 JPA 时，需要允许 JPA 提供者管理实体实例之间的关系。在给定的情况下，通过跟踪各种外键标识符来手动管理关系。因此，JPA 提供程序无法设置外键列值。

基本问题似乎在于理解 JPA(或任何其他 ORM)的工作原理。实体不是数据库表的逐列副本。需要将它们视为对象并建模为对象，而无需考虑底层数据库。实体属性到数据库列的映射应留给 JPA 提供程序。

---

以下实体模型将解决该问题(为简洁起见，删除了所有不必要的代码):

ParentOne entity

@Entity
@Table(name="ParentOne", schema="S1")
public class ParentOne {
  @Id
  @Column(name="ParentOneID", unique=true, nullable=false)
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer id;

  @OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL, mappedBy="parentOne")
  private List<Child> children;

  public void addChild(final Child child) {
    if (children == null) {
      children = new ArrayList<>();
    }

    children.add(child);

    child.setParentOne(this);
  }
}

以下几点值得注意:

1. 模式名称 (S1) 已与实体实例必须持久保存到的表名称一起声明。
2. 与子实体的关系声明为一个集合，并注解为@OneToMany。
3. 持久性操作(保存、更新、删除)级联到子实体实例 (cascade = CascadeType.ALL)。这可确保对父实例的持久性操作自动处理对任何关联子实例的适当操作。

ParentTwo entity

@Entity
@Table(name="ParentTwo", schema="S2")
public class ParentTwo {
  @Id
  @Column(name="ParentTwoID", unique=true, nullable=false)
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer id;

  @OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL, mappedBy="parentTwo")
  private List<Child> children;

  public void addChild(final Child child) {
    if (children == null) {
      children = new ArrayList<>();
    }

    children.add(child);

    child.setParentTwo(this);
  }
}

Child entity

@Entity
@Table(name="ChildTable", schema="S2")
public class Child {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name="ChildTableID", unique=true, nullable=false)
  private Integer id;

  @ManyToOne(cascade=CascadeType.PERSIST)
  @JoinColumn(name="ParentOneID", nullable=false)
  private ParentOne parentOne;

  @ManyToOne(cascade=CascadeType.PERSIST)
  @JoinColumn(name="ParentTwoID", nullable=false)
  private ParentTwo parentTwo;

  void setParentOne(final ParentOne parentOne) {
    this.parentOne = parentOne;
  }

  void setParentTwo(final ParentTwo parentTwo) {
    this.parentTwo = parentTwo;
  }
}

以下几点值得注意:

1. 架构名称 (S2) 与表名称一起声明。
2. 与父表的关联声明为对象实例，而不是原始列。

在此之后，以下代码将正常工作:

Child child = new Child();
...

ParentOne parentOne = new ParentOne();
ParentTwo parentTwo = new ParentTwo();
...

parentOne.addChild(child);
parentTwo.addChild(child);

parentOneRepository.save(parentOne);