java JPA @Entity 继承
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JPA @Entity Inheritance
提问by travega
I have been looking into JPA/Hibernate @Entityinheritance for a while now and can't seem to find anything that addresses what I am trying to achieve.
我已经研究 JPA/Hibernate@Entity继承有一段时间了，似乎找不到任何可以解决我想要实现的目标的东西。
Basically I want to be able to define an @Entitywith all of the column and table mappings as required. Then I want to be able to extend the @Entityin a number of different locations with different sets of @Transientmethods defined in the body of each "sub-Entity". This is a basic example of what I am trying to achieve but with no success thus far:
基本上我希望能够根据需要定义@Entity所有列和表映射。然后我希望能够使用@Entity在@Transient每个“子实体”的主体中定义的不同方法集在许多不同的位置扩展。这是我试图实现但迄今为止没有成功的基本示例：
@Entity
@Table(name = "mountain")
public class MountainEntityBase implements Serializable {
public Integer mountainId = 0;
public Integer height = 0;
public List<ExplorerEntityBase> explorers = new ArrayList<ExplorerEntityBase>();
@Id
@GeneratedValue
@Column(name = "mountain_id")
public Integer getMountainId() { return mountainId; }
public void setMountainId(Integer mountainId) { this.mountainId = mountainId; }
@Column(name="height")
public String getHeight() { return height; }
public void setHeight(String height) { this.height = height; }
@OneToMany(mappedBy="mountainId")
public List<ExplorerEntityBase> getExplorers() { return this.explorers; }
public void setExplorers(List<ExplorerEntityBase> explorers) { this.explorers = explorers; }
}
.
.
@Entity
public class MountainEntity extends MountainEntityBase implements Serializable {
public List<MountainEntity> allMountainsExploredBy = new ArrayList<MountainEntity>();
@Transient
public List<MountianEntity> getAllMountainsExploredBy(String explorerName){
// Implementation
}
}
So any extended class will define only @Transients in its body. But also I want to allow for situations where the child class is empty:
因此，任何扩展类将只@Transient在其主体中定义s。但我也想允许子类为空的情况：
@Entity
public class MountainEntity extends MountainEntityBase implements Serializable {
}
Thanks in advance for any help with this.
在此先感谢您的帮助。
回答by Bozho
Inheritance in JPA is specified on the root entity using the @Inheritanceannotation. There you can specify the database representation of the hierarchy. Check the documentationfor more details.
JPA 中的继承是使用@Inheritance注释在根实体上指定的。您可以在那里指定层次结构的数据库表示。查看文档以获取更多详细信息。
If your child classes define only transient fields (not methods) (i.e. not saved in the db), then perhaps a discriminator column is the best option. But it may be the case that you don't actually need inheritance - the main entity can have all the methods (because it has all the fields the methods operate on)
如果您的子类仅定义瞬态字段（而不是方法）（即未保存在 db 中），那么鉴别器列可能是最佳选择。但可能是您实际上不需要继承的情况 - 主实体可以拥有所有方法（因为它拥有方法操作的所有字段）
