对于某个Hibernate实体,我们需要存储它的创建时间和最后一次更新时间。你会怎么设计呢?

您将在数据库中使用什么数据类型(假设MySQL,可能位于与JVM不同的时区)?数据类型是否支持时区? 你会在Java中使用什么数据类型(日期,日历,长,…)? 您会让谁负责设置时间戳——数据库、ORM框架(Hibernate)还是应用程序程序员? 你会为映射使用什么注释(例如@Temporal)?

我不仅在寻找一个可行的解决方案,而且在寻找一个安全、设计良好的解决方案。


当前回答

利用本文中的资源以及来自不同来源的左右信息,我提出了这个优雅的解决方案,创建以下抽象类

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.MappedSuperclass;
import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@MappedSuperclass
public abstract class AbstractTimestampEntity {

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "created", nullable = false)
    private Date created;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "updated", nullable = false)
    private Date updated;

    @PrePersist
    protected void onCreate() {
    updated = created = new Date();
    }

    @PreUpdate
    protected void onUpdate() {
    updated = new Date();
    }
}

并让你的所有实体扩展它,例如:

@Entity
@Table(name = "campaign")
public class Campaign extends AbstractTimestampEntity implements Serializable {
...
}

其他回答

如果你正在使用JPA注释,你可以使用@PrePersist和@PreUpdate事件钩子来做到这一点:

@Entity
@Table(name = "entities")    
public class Entity {
  ...

  private Date created;
  private Date updated;

  @PrePersist
  protected void onCreate() {
    created = new Date();
  }

  @PreUpdate
  protected void onUpdate() {
    updated = new Date();
  }
}

或者您可以在类上使用@EntityListener注释,并将事件代码放在外部类中。

谢谢所有帮助过我的人。在我自己做了一些研究之后(我是问这个问题的人),以下是我发现最有意义的:

Database column type: the timezone-agnostic number of milliseconds since 1970 represented as decimal(20) because 2^64 has 20 digits and disk space is cheap; let's be straightforward. Also, I will use neither DEFAULT CURRENT_TIMESTAMP, nor triggers. I want no magic in the DB. Java field type: long. The Unix timestamp is well supported across various libs, long has no Y2038 problems, timestamp arithmetic is fast and easy (mainly operator < and operator +, assuming no days/months/years are involved in the calculations). And, most importantly, both primitive longs and java.lang.Longs are immutable—effectively passed by value—unlike java.util.Dates; I'd be really pissed off to find something like foo.getLastUpdate().setTime(System.currentTimeMillis()) when debugging somebody else's code. The ORM framework should be responsible for filling in the data automatically. I haven't tested this yet, but only looking at the docs I assume that @Temporal will do the job; not sure about whether I might use @Version for this purpose. @PrePersist and @PreUpdate are good alternatives to control that manually. Adding that to the layer supertype (common base class) for all entities, is a cute idea provided that you really want timestamping for all of your entities.

对于那些想要使用JPA和Spring Data创建或修改用户详细信息以及时间的人,可以遵循这一点。你可以在base域中添加@CreatedDate,@LastModifiedDate,@CreatedBy和@LastModifiedBy。用@MappedSuperclass和@EntityListeners(AuditingEntityListener.class)标记基域,如下所示:

@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
public class BaseDomain implements Serializable {

    @CreatedDate
    private Date createdOn;

    @LastModifiedDate
    private Date modifiedOn;

    @CreatedBy
    private String createdBy;

    @LastModifiedBy
    private String modifiedBy;

}

因为我们用AuditingEntityListener标记了基本域,所以我们可以告诉JPA当前登录的用户。因此,我们需要提供AuditorAware的实现并重写getCurrentAuditor()方法。在getCurrentAuditor()内部,我们需要返回当前授权的用户Id。

public class AuditorAwareImpl implements AuditorAware<String> {
    @Override
    public Optional<String> getCurrentAuditor() {
        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
        return authentication == null ? Optional.empty() : Optional.ofNullable(authentication.getName());
    }
}

在上面的代码中,如果Optional不能工作,你可以使用Java 7或更老的版本。在这种情况下,尝试用String改变Optional。

现在使用下面的代码来启用上述审计器实现

@Configuration
@EnableJpaAuditing(auditorAwareRef = "auditorAware")
public class JpaConfig {
    @Bean
    public AuditorAware<String> auditorAware() {
        return new AuditorAwareImpl();
    }
}

现在,您可以将BaseDomain类扩展到您需要创建和修改日期和时间以及用户Id的所有实体类

利用本文中的资源以及来自不同来源的左右信息,我提出了这个优雅的解决方案,创建以下抽象类

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.MappedSuperclass;
import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@MappedSuperclass
public abstract class AbstractTimestampEntity {

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "created", nullable = false)
    private Date created;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "updated", nullable = false)
    private Date updated;

    @PrePersist
    protected void onCreate() {
    updated = created = new Date();
    }

    @PreUpdate
    protected void onUpdate() {
    updated = new Date();
    }
}

并让你的所有实体扩展它,例如:

@Entity
@Table(name = "campaign")
public class Campaign extends AbstractTimestampEntity implements Serializable {
...
}

下面的代码对我有用。

package com.my.backend.models;

import java.util.Date;

import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;

import com.fasterxml.jackson.annotation.JsonIgnore;

import org.hibernate.annotations.ColumnDefault;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

import lombok.Getter;
import lombok.Setter;

@MappedSuperclass
@Getter @Setter
public class BaseEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Integer id;

    @CreationTimestamp
    @ColumnDefault("CURRENT_TIMESTAMP")
    protected Date createdAt;

    @UpdateTimestamp
    @ColumnDefault("CURRENT_TIMESTAMP")
    protected Date updatedAt;
}