How persist two objects related to each other at the same time?

Question

I am trying to persist a new JobAdvertise object with a list of new JobAdTasks objects. An advertise contains tasks related to it, both persisted successfully at the same time. However, the foreign key for each JobAdTask is empty. How can I solve this problem, persisting two objects at the same in a two-way mapping relationship?

JobAdvertise class:

@JsonManagedReference
@OneToMany(cascade = CascadeType.ALL,mappedBy = "jobAdvertise")
private List<JobAdTask> taskList = new ArrayList<>();

public void addTask(JobAdTask adTask) {
   if (adTask != null) {
      if (taskList == null) { taskList = new ArrayList<>(); }
      taskList.add(adTask);
   }
}

JobAdTask class:

@JsonBackReference
@ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.DETACH, CascadeType.MERGE, CascadeType.REFRESH}, fetch = FetchType.LAZY)
@JoinColumn(name = "job_add_id")
private JobAdvertise jobAdvertise;

JobAdvertiseService service class:

JobAdvertise jobAdvertise = new JobAdvertise();

for (String task : jobAdCreation.getTaskList()) {
   JobAdTask jobAdTask = new JobAdTask();
   jobAdTask.setTask(task);
   jobAdTaskRepo.save(jobAdTask);
   
   //Relationship JobAdvertise and JobAdTask
   jobAdvertise.addTask(jobAdTask);
}

jobAdvertiseRepo.save(jobAdvertise);

I think there is a problem on json serialization level connected to `JsonManagedReference` and `JsonBackReference` see https://stackoverflow.com/questions/71991102/spring-data-jpa-findall-does-not-return-relations-data/71993222#71993222 — Eugene, May 07 '22 at 22:25

tbjorch · Accepted Answer · 2022-05-09T07:22:24.520

In your service, you need to change to the following:

for (String task : jobAdCreation.getTaskList()) {
   JobAdTask jobAdTask = new JobAdTask();
   jobAdTask.setTask(task);
   jobAdTask.setJobAdvertise(jobAdvertise);
   jobAdTask = jobAdTaskRepo.save(jobAdTask); // Also re-assign the jodAdTask variable since otherwise the id and any timestamps managed by the ORM won't be available in your object.
   
   //Relationship JobAdvertise and JobAdTask
   jobAdvertise.addTask(jobAdTask);
}

An option would be to re-write the code as following:

// in JobAdvertise
public void addTask(JobAdTask adTask) {
   if (adTask != null) {
      adTask.setJobAdvertise(this); // Link the objects here
      if (taskList == null) { taskList = new ArrayList<>(); }
      taskList.add(adTask);
   }
}

public void addTasks(Collection<JobAdTask> adTasks) { // add this method to enable passing a collection to the object, removing the need for iteration from the service class.
   adTasks.forEach(this::addTask);
}

// in JobAdTask create a constructor taking a string

public JobAdTask(String task) {
   this.setTask(task);
}

// in JobAdvertiseService
List<JobAdTask> jobAdTasks = jobAdCreation.getTaskList().stream().map(JobAdTask::new).collect(Collectors.toList()); // creates list of jobAdTasks using the constructor taking a String argument

JobAdvertise jobAdvertise = new JobAdvertise();
jobAdvertise.addTasks(jobAdTasks); // the addTasks uses the addTask method of jobAdvertise, which links the JobAdvertise object and each JobAdTask object.
jobAdvertise = jobAdvertiseRepo.save(jobAdvertise); // when you save the JobAdvertise, since you use CascadeType.ALL, both the advertise and each task object will be persisted to the database.

How persist two objects related to each other at the same time?

1 Answers1

In your service, you need to change to the following:

An option would be to re-write the code as following: