Issue with saving entities with associations (ManyToMany) while using REST API - rest

Question

I have a Spring REST application. The application has few entities like Question, PossibleAnswer.
These entities are as follows:
Question.java
public class Question {
#Id
#Column(name = "id")
#GeneratedValue
private UUID id;
//some other fields here
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable( name = "possibleanswer_question",
joinColumns = #JoinColumn(name = "question_id"),
inverseJoinColumns = #JoinColumn(name = "possible_answer_id"))
#EqualsAndHashCode.Exclude
private Set<PossibleAnswer> possibleAnswers = new HashSet<>();
}
PossibleAnswer.java
public class PossibleAnswer {
#Id
#Column(name = "id")
#GeneratedValue
private UUID id;
#JsonIgnore
#ManyToMany(mappedBy = "possibleAnswers")
#EqualsAndHashCode.Exclude
private Set<Question> questions = new HashSet<>();
}
on REST controller side I used PUT request to assign each PossibleAnswer to Question like the following.
#PutMapping(
path = "/{questionId}/possibleAnswers/{possibleAnswerId}"
)
public QuestionDTOResponse assignPossibleAnswerToQuestion(
#PathVariable UUID questionId,
#PathVariable UUID possibleAnswerId
){
Question questionById = questionService.findQuestionById(questionId);
PossibleAnswer possibleAnswerById = possibleAnswerService.findPossibleAnswerById(possibleAnswerId);
questionById.addPossibleAnswerToQuestion(possibleAnswerById);// custom method to add PossibleAnswer to Question
Question savedQuestion = questionService.saveQuestion(questionById);
return mapToQuestionResponse(savedQuestion);
}
This endpoint works only if I create Question and PossibleAnswer separately, later we can assign PossibleAnswer to Question.
But when I try to save Question using the following api endpoint (POST endpoint shown below) to save Question with PossibleAnswer together, there just a new Question gets created with no PossibleAnswer.
#PostMapping(
consumes = MediaType.APPLICATION_JSON_VALUE,
produces = MediaType.APPLICATION_JSON_VALUE
)
public QuestionDTOResponse createQuestion( #RequestBody QuestionDTORequest questionDTORequest ){
Question savedQuestion = questionService.saveQuestion(mapToQuestion(questionDTORequest));
return mapToQuestionResponse(savedQuestion);
}
The request to save Question looks like this.
{
"text" : "Question 9",
"comment": "some comment about the question",
"possibleAnswers": [
{
"text": "possible answer 19"
}
]
}
The save method implementation is as follows:
public Question saveQuestion(Question question) {
return questionRepository.save(question);
}
I have three questions here:
Am I doing the save operation with entities correctly, or is there any better way of doing this.
This is the backend side of the application, how to handle the request frontend when the request JSON has PossibleAnswer with Question togther.
Why is the save operation not working correctly.
Could anyone please help me with these queries?