我有以下问题：

Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Error while committing the transaction

以及：

Caused by: java.util.ConcurrentModificationException: null

我知道问题出在哪里了。
我尝试更新子实体，即与父实体的关系。当我更新孩子时，刷新效果不好。如果我换了父母，孩子也会留下。这不好。所以，我尝试获取“旧”父对象，从列表中删除子对象，然后继续更新。但是当我移除子对象时，它触发了@preremove注解。我不想那样。
孩子来了：

@Entity
@Table(name = "job", schema = "public")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Job implements Serializable {
...
...
    @ManyToOne(cascade = CascadeType.REFRESH,fetch = FetchType.LAZY)
    @OnDelete(action = OnDeleteAction.CASCADE)
    @JsonIgnoreProperties(value = "jobs", allowSetters = true)
    private Project project;
..
...
...
    public Project getProject() {
        return project;
    }

    public Job project(Project project) {
        this.project = project;
        return this;
    }

    public void setProject(Project project) {
        this.project = project;

    }
...
...
...
    @PreRemove
    public void removeAppUsers() {

        if(this.appUsers.size()>0)
        for (AppUser ap : this.appUsers) {
            ap.removeJob(this);
        }
        if(this.performances.size()>0)
        for (Performance p : this.performances) {
            p.setJob(null);
        }
    }

服务（@service，@transactional）：

public JobDTO save(JobDTO jobDTO) {
        Optional<Project> projectToRemove;
        Project p;
        log.debug("Request to save Job : {}", jobDTO); 
        Job job = jobMapper.toEntity(jobDTO);
        projectToRemove=projectRepository.findProjectByJob(jobDTO.getId());
        jobRepository.save(job);
        if(projectToRemove.isPresent()&&jobDTO.getProjectId()!=projectToRemove.get().getId()) {
                projectToRemove.get().removeJob(job);
                projectRepository.save(projectToRemove.get());
        }     
        if (jobDTO.getProjectId() != null) {

            p = projectRepository.findById(jobDTO.getProjectId()).get();
            p.addJob(job);
            projectRepository.save(p);
            job.setProject(p);
            jobRepository.save(job);
        }
....
}

你知道吗？
编辑1：
删除作业：

public Project removeJob(Job job) {
    this.jobs.remove(job);
    job.setProject(null);
    return this;
}

编辑2：
项目：

@OneToMany(mappedBy = "project", cascade = CascadeType.ALL, orphanRemoval = true)
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
private Set<Job> jobs = new HashSet<>();