[FIXED] Spring Boot save nested Entity with JSON RequestBody

Issue

I'm trying to create a Rest API for a school project.Therefor I'm trying to save/edit a nested Object. I have two bidirectional entities which look like this:

EntityA

 @Entity
    public class EntityA {
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Id
        @Column(name = "id", nullable = false)
        @JsonProperty("id")
        private int id;
    
        @Column(name = "field1", nullable = false, length = -1)
        @JsonProperty("field1")
        private String field1;
    
        @Column(name = "field2", nullable = false, length = -1)
        @JsonProperty("field2")
        private String field2;
    
        @OneToMany(mappedBy = "entityA", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
        @JsonProperty("entityB")
        private List<EntityB> entityB;
    
        public EntityA() {
    
        }
        
        //Getter+Setter
        
    }

EntityB

@Entity
public class EntityB {
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    @Column(name = "id", nullable = false)
    @JsonProperty("id")
    private int id;

    @Column(name = "field1", nullable = false)
    @JsonProperty("field1")
    private Date field1;

    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(...)
    @JsonProperty("entityA")
    private EntityA entityA;

    public EntityB() {

    }
    
   //Getter+Setter
}

As RequestBody I will get JSON which should look like this.

{
     "field1": "Test",
     "field2": "User",
     "entityB": [
            {
                "field1": "30.03.2022"
            }
        ]
}

Right now Spring will automatically map the fields but as soon I try to save it to my DB I will get an error, because the relation in EntityB for EntityA is empty. I've seen a solution, that I should loop through the EntityB list and add EntityA. I tried it with a for-each but it still sais it null.

What am I doing wrong?

public EntityA createEntityA(EntityA entityA) {
        for(EntityB entityB : entityA.getEntityB()){
            entityB.setEntityA(entityA);
        }
        return entityARepository.save(entityA);
    }

Edit:

Controller

@PostMapping(value = {"/json/entitya/"})
@ResponseBody
public EntityA createEntityAJson(@RequestBody EntityA entityA) {
    return entityAService.createEntityA(entityA);
}

Service

@Service
public class EntityAService {

    @Autowired
    private EntityARepository entityARepository;

    public EntityA createEntityA(EntityA entityA) {
        return entityARepository.save(entityA); //in this line the error appears
    }
}

Error message

null value in column "entityA" violates not-null constraint

Solution

@Service
public class EntityAService {
    
        @Autowired
        private EntityARepository entityARepository;
        @Autowired
        private EntityBRepository entityBRepository;
    
        public EntityA createEntityA(EntityA entityA) {

      // create an empty arrayList to stock the entities B retrieveed from the DB
       List<EnityB> lst = new ArrayList<>();
        
        // get the entities B from the JSON and sabe it to the DB    
        for(EntityB entityB : entityA.getEntityB()){
        entityB.setEntityA(entityA);
        entityBRepository.save(entityB);  // you should save entities B to the DataBase before
        Optional<EntityB > opt = entityBRepository.findById(entityB.getId());
        EntityB b = opt.get();
        
        // add the entities B retrieved from the DB to the arrayList
        lst.add(b);
        }
        
        // set the EntityB list with the new List from the DB ( include ids ..)
        entityA.setEntityB(lst);
         
        // save the entityA to the DB
            return entityARepository.save(entityA); 
        }
    }

Answered By - Oussama ZAGHDOUD
Answer Checked By - Marie Seifert (JavaFixing Admin)