Question

我有以下Java类：

public Class Parent {

    int someValue1;

    ChildType child;
}


public Class ChildType {

     int someValue2;
}


public Class ChildA extends ChildType {

     int id;

     String string;
}



public Class ChildB extends ChildType {

    int id;

    Integer integer;
}

我需要将Parent，ChildA和ChildB表示为实体bean，每个实体bean在数据库中都有一个相关的表。

当我加载Parent时，我还需要加载ChildA或ChildB，具体取决于关系。

Answer 1

如果我说得对，那么class parent是一个与ChildType实体保持一对一关系的实体。 ChildType也是一个抽象实体，有2个实现，ChildA和ChildB。

因此，每个实体的JPA注释配置可能是这样的：

 Parent class as Entity

@Entity
@Table(name = "PARENT")
public class Parent { // better name will do the job, because parent is often called
                      // the higher level class of the same hierarchy
  @Id
  @GeneratedValue
  @Column(name = "PARENT_ID")
  private long id;

  @Column(name = "SOME_VALUE") //if you need to persist it
  private int someValue1;

  @OneToOne(optional = false, cascade = CascadeType.ALL)
  @JoinColumn(name = "FK_PARENT_ID")
  private ChildType child;

  // getters and setters
}

 ChildType class as Entity

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class ChildType { // this one is actually called parent class

  @Id
  @GeneratedValue(strategy = GenerationType.TABLE)
  @Column(name = "CHILDTYPE_ID")
  protected Long id;

  @Column(name = "SOME_VALUE_2")
  private int someValue2; // or maybe protected. Depends if you need childs to access it

  @Column(name = "A_STRING")
  private String string; // or maybe protected. Depends if you need childs to access it

  // getters and setters
}

最后我们有ChildA和ChildB

正如您所看到的，ChildType子类上不需要id字段，因为他们从ChildType继承这个字段！

 ChildA as Entity

@Entity
@Table(name = "CHILD_A")
public Class ChildA extends ChildType {

  @Column(name = "A_STRING")
  private String string;

  // getters and setters
}

 ChildB as Entity

@Entity
@Table(name = "CHILD_B")
public Class ChildB extends ChildType {

  @Column(name = "AN_Integer")
  private Integer integer;

  // getters and setters
}

有关JPA继承

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JPA实体：如何在Parent和多个Child类之间建立关系

1 个答案:

最后我们有ChildA和ChildB

有关JPA继承