MappedSuperclass

我们对许多实体 Bean 使用 @MappedSuperclass 来获取通用属性。

使用 @Id@Version@WhenModified 属性的映射超类很常见,如下面的示例所示,并且映射超类扩展 Model 也很常见。

package org.example.domain;

import io.ebean.Model;
import io.ebean.annotation.WhenCreated;
import io.ebean.annotation.WhenModified;

import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import javax.persistence.Version;
import java.time.Instant;

/**
 * Base domain object with Id, version, whenCreated and whenModified.
 */
@MappedSuperclass
public abstract class BaseDomain extends Model {

  @Id
  long id;

  @Version
  Long version;

  @WhenCreated
  Instant whenCreated;

  @WhenModified
  Instant whenModified;

  // getters and setters
  ...

}
  
package org.example.domain

import io.ebean.annotation.WhenCreated
import io.ebean.annotation.WhenModified
import java.time.Instant
import javax.persistence.Id
import javax.persistence.MappedSuperclass
import javax.persistence.Version

@MappedSuperclass
open class BaseDomain : Model() {

  @Id
  var id: Long = 0

  @Version
  var version: Long = 0

  @WhenModified
  lateinit var whenModified: Instant

  @WhenCreated
  lateinit var whenCreated: Instant

}
  

然后,我们的实体 Bean 扩展它来继承通用属性。

Customer 扩展 BaseDomain

...
@Entity
public class Customer extends BaseDomain {

  String name;

  LocalDate registered;
  ...
  
package org.example.domain

import javax.persistence.Entity

@Entity
class Customer : BaseDomain() {

  var name: String? = null
}
  

Kotlin 有多种构造函数样式。有关实体 Bean 的首选构造函数样式的更多信息,请参阅 此处