Question

我有一个具有瞬态字段的实体。当我想创建对象的新实例时，我会丢失我的瞬态信息。以下示例演示了此问题。为了举例，我们可以说barness是一个瞬态场。

FooEntity fooEntity = new FooEntity();
fooEntity.setFoobosity(5);
fooEntity.setBarness(2);
fooEntity = fooEntityManager.merge(fooEntity);
System.out.println(fooEntity.getFoobosity()); //5
System.out.println(fooEntity.getBarness()); //0 (or whatever default barness is)

有没有办法维护我的瞬态信息？

Answer 1

这或多或少都按设计工作。瞬态的语义恰恰是the data is not persisted。事实上，从entityManager.merge(obj)返回的实体是一个全新的实体，它维护传递给合并的对象的状态（状态，在此上下文中，是不属于持久对象的任何东西）。这在the JPA spec中有详细说明。注意：可能有JPA实现在合并对象后维护瞬态字段（仅仅因为它们返回相同的对象），但规范不保证这种行为。

你可以做两件事：

决定保持瞬态场。如果在将类合并到持久化上下文后需要它，它似乎并不是暂时的。
维持持久对象之外的瞬态字段的值。如果这符合您的需求，您可能需要重新考虑域类的结构;如果这个字段不是域对象状态的一部分，它实际上不应该存在。

最后一件事：我在域类的瞬态字段中发现的主要用例是划分派生字段，即可以根据类的持久字段重新计算的字段。

Answer 2

迟到加入讨论，但这就是我使用 spring AOP和JPA提供@PreUpdate注释（添加详细版本）

的方法

使用案例

如果从UI进行更改，我们应该使用Spring提供的审核实体
如果通过API而不是通过前端服务进行更改，我们希望使用客户提供的自己的值覆盖值（@ LastModifiedBy和@LastModifiedDate）
实体具有瞬态值（backendModifiedDate，backendAuditor），需要在保存后合并（遗憾的是Spec不保证这一点）。这两个字段将保存来自外部服务的审计数据
在我们的案例中，我们需要一个通用的解决方案来审核所有实体。

Db配置

    package config;

    import io.github.jhipster.config.JHipsterConstants;
    import io.github.jhipster.config.liquibase.AsyncSpringLiquibase;

    import liquibase.integration.spring.SpringLiquibase;
    import org.h2.tools.Server;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.boot.autoconfigure.liquibase.LiquibaseProperties;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.Profile;
    import org.springframework.core.env.Environment;
    import org.springframework.core.task.TaskExecutor;
    import org.springframework.data.jpa.repository.config.EnableJpaAuditing;
    import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
    import org.springframework.transaction.annotation.EnableTransactionManagement;

    import javax.sql.DataSource;
    import java.sql.SQLException;

    @Configuration
    @EnableJpaRepositories("repository")
    @EnableJpaAuditing(auditorAwareRef = "springSecurityAuditorAware")
    @EnableTransactionManagement
    public class DatabaseConfiguration {

        private final Logger log = LoggerFactory.getLogger(DatabaseConfiguration.class);

        private final Environment env;

        public DatabaseConfiguration(Environment env) {
            this.env = env;
        }
        /* Other code */
    }

用于注入用户名的SpringSecurityAuditorAware

package security;

import config.Constants;

import org.springframework.data.domain.AuditorAware;
import org.springframework.stereotype.Component;

/**
 * Implementation of AuditorAware based on Spring Security.
 */
@Component
public class SpringSecurityAuditorAware implements AuditorAware<String> {

    @Override
    public String getCurrentAuditor() {
        String userName = SecurityUtils.getCurrentUserLogin();
        return userName != null ? userName : Constants.SYSTEM_ACCOUNT;
    }
}

抽象实体与JPA @PreUpdate
这实际上会设置@ LastModifiedBy和@LastModifiedDate字段的值

package domain;

import com.fasterxml.jackson.annotation.JsonIgnore;
import org.hibernate.envers.Audited;
import org.springframework.data.annotation.CreatedBy;
import org.springframework.data.annotation.CreatedDate;
import org.springframework.data.annotation.LastModifiedBy;
import org.springframework.data.annotation.LastModifiedDate;
import org.springframework.data.jpa.domain.support.AuditingEntityListener;

import javax.persistence.Column;
import javax.persistence.EntityListeners;
import javax.persistence.MappedSuperclass;
import javax.persistence.PreUpdate;
import java.io.Serializable;
import java.time.Instant;

/**
 * Base abstract class for entities which will hold definitions for created, last modified by and created,
 * last modified by date.
 */
@MappedSuperclass
@Audited
@EntityListeners(AuditingEntityListener.class)
public abstract class AbstractAuditingEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    @CreatedBy
    @Column(name = "created_by", nullable = false, length = 50, updatable = false)
    @JsonIgnore
    private String createdBy;

    @CreatedDate
    @Column(name = "created_date", nullable = false)
    @JsonIgnore
    private Instant createdDate = Instant.now();

    @LastModifiedBy
    @Column(name = "last_modified_by", length = 50)
    @JsonIgnore
    private String lastModifiedBy;

    @LastModifiedDate
    @Column(name = "last_modified_date")
    @JsonIgnore
    private Instant lastModifiedDate = Instant.now();

    private transient String backendAuditor;

    private transient Instant backendModifiedDate;

    public String getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(String createdBy) {
        this.createdBy = createdBy;
    }

    public Instant getCreatedDate() {
        return createdDate;
    }

    public void setCreatedDate(Instant createdDate) {
        this.createdDate = createdDate;
    }

    public String getLastModifiedBy() {
        return lastModifiedBy;
    }

    public void setLastModifiedBy(String lastModifiedBy) {
        this.lastModifiedBy = lastModifiedBy;
    }

    public Instant getLastModifiedDate() {
        return lastModifiedDate;
    }

    public void setLastModifiedDate(Instant lastModifiedDate) {
        this.lastModifiedDate = lastModifiedDate;
    }

    public String getBackendAuditor() {
        return backendAuditor;
    }

    public void setBackendAuditor(String backendAuditor) {
        this.backendAuditor = backendAuditor;
    }

    public Instant getBackendModifiedDate() {
        return backendModifiedDate;
    }

    public void setBackendModifiedDate(Instant backendModifiedDate) {
        this.backendModifiedDate = backendModifiedDate;
    }

    @PreUpdate
    public void preUpdate(){
        if (null != this.backendAuditor) {
            this.lastModifiedBy = this.backendAuditor;
        }
        if (null != this.backendModifiedDate) {
            this.lastModifiedDate = this.backendModifiedDate;
        }
    }
}

合并后合并保留数据的方面
这将拦截对象（实体）并重置字段

package aop.security.audit;


import domain.AbstractAuditingEntity;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import java.time.Instant;

@Aspect
@Component
public class ExternalDataInflowAudit {
    private final Logger log = LoggerFactory.getLogger(ExternalDataInflowAudit.class);

    // As per our requirements, we need to override @LastModifiedBy and @LastModifiedDate
    // https://stackoverflow.com/questions/2581665/jpa-transient-information-lost-on-create?answertab=active#tab-top
    @Around("execution(public !void javax.persistence.EntityManager.merge(..))")
    private Object resetAuditFromExternal(ProceedingJoinPoint joinPoint) throws Throwable {
        Object[] args = joinPoint.getArgs();
        AbstractAuditingEntity abstractAuditingEntity;
        Instant lastModifiedDate = null;
        String lastModifiedBy = null;
        if (args.length > 0 && args[0] instanceof AbstractAuditingEntity) {
            abstractAuditingEntity = (AbstractAuditingEntity) args[0];
            lastModifiedBy = abstractAuditingEntity.getBackendAuditor();
            lastModifiedDate = abstractAuditingEntity.getBackendModifiedDate();
        }
        Object proceed = joinPoint.proceed();
        if (proceed instanceof AbstractAuditingEntity) {
            abstractAuditingEntity = (AbstractAuditingEntity) proceed;
            if (null != lastModifiedBy) {
                abstractAuditingEntity.setLastModifiedBy(lastModifiedBy);
                abstractAuditingEntity.setBackendAuditor(lastModifiedBy);
                log.debug("Setting the Modified auditor from [{}] to [{}] for Entity [{}]",
                    abstractAuditingEntity.getLastModifiedBy(), lastModifiedBy, abstractAuditingEntity);
            }
            if (null != lastModifiedDate) {
                abstractAuditingEntity.setLastModifiedDate(lastModifiedDate);
                abstractAuditingEntity.setBackendModifiedDate(lastModifiedDate);
                log.debug("Setting the Modified date from [{}] to [{}] for Entity [{}]",
                    abstractAuditingEntity.getLastModifiedDate(), lastModifiedDate, abstractAuditingEntity);
            }
        }
        return proceed;
    }
}

<强>用法
如果实体具有backendAuditor和/或backendModifiedDate设置，那么将使用此值，否则将采用Spring Audit提供的值。

最后归功于Jhipster，它简化了很多事情，使您可以专注于业务逻辑。

免责声明：我只是Jhipster的粉丝，无论如何都与它无关。

Answer 3

基于@Prassed惊人的answer，我创建了一个更通用的代码：

我需要在实体上允许一些临时字段（我的意思是我们不保留在数据库中的字段，但是我们允许用户用我们发送给服务器的数据填充它们[使用@JsonSerialize / @JsonDeserialize]并上传到文件存储。

这些字段将带有以下注释（RetentionPolicy。此处使用RUNTIME，因此我可以在运行时对这些字段使用反射）：

@Retention(RetentionPolicy.RUNTIME)
public @interface PreservePostMerge { }

然后，我使用apache的FieldUtil遍历这些字段：

@Aspect
@Component
public class PreservePostMergeData {

    private final Logger log = LoggerFactory.getLogger(PreservePostMergeData.class);

    @Around("execution(public !void javax.persistence.EntityManager.merge(..))")
    private Object preserveTransientDataPostMerge(ProceedingJoinPoint joinPoint) throws Throwable {

        Object[] args = joinPoint.getArgs();
        Object afterMerge = joinPoint.proceed();
        if (args.length > 0) {
            Object beforeMerge = args[0];

            Field[] annotatedFieldsToPreserve = FieldUtils.getFieldsWithAnnotation(beforeMerge.getClass(), PreservePostMerge.class);
            Arrays.stream(annotatedFieldsToPreserve).forEach(field -> {
                try {
                    FieldUtils.writeField(field, afterMerge, FieldUtils.readField(field, beforeMerge, true), true);
                } catch (IllegalAccessException exception) {
                    log.warn("Illegal accesss to field: {}, of entity: {}. Data was not preserved.", field.getName(), beforeMerge.getClass());
                }
            });
        }

        return afterMerge;
    }
}

JPA瞬态信息在创建时丢失

3 个答案: