Spring, accessing method from a different controller

Question

I got an entity B bound by a ManyToOne with another Entity A. Writing add method in its controller I obviously pass a field of an Instance of A as a parameter, from which I select the whole object to extract its ID that I use as the key for the relationship. If the instance of A I'm trying to select is non-existent, I want it to be created (the field I'm passing as a parameter is enough for its constructor). Can I do that without instantiating Controller A inside Controller B? It seems weird...

UPDATE I rewrote most part of my project, thanks to the hints by @Artur Vakhrameev

I created a service for every entities and instantiated one of them inside the other one. This is the service for the "many side" relationship entity

@Transactional
@Service
public class LineaService {

    @Autowired
    private LineaRepository lineaRepo;
    @Autowired
    private MarcaService marcaService;

    public Linea create(Linea linea) {
        Linea nuovaLinea = new Linea();
        nuovaLinea.setNome(linea.getNome());

        if (marcaService.findByName(linea.getMarca().getNome()) == null)
            nuovaLinea.setMarca(marcaService.create(linea.getMarca()));
        else
            nuovaLinea.setMarca(linea.getMarca());

        lineaRepo.save(nuovaLinea);

        nuovaLinea.getMarca().addLinea(nuovaLinea);

        return nuovaLinea;
    }

And this is now the simple add postmapping in my controller, stripped of all the business logic

@PostMapping("/add")
    public String aggiungiLinea(Linea linea) {
        lineaService.create(linea);
        return "redirect:list";
    }

UPDATE 2 (this one seems to work as expected)

public Linea create(Linea linea) {
    Marca marcaAssociata = marcaService.findByName(linea.getMarca().getNome());
    if (marcaAssociata == null) 
        linea.setMarca(marcaService.create(linea.getMarca()));
    else
        linea.setMarca(marcaAssociata);

    return lineaRepo.save(linea);
}

Answer 1

If i understand you correctly:

1. You don't need a controller A inside B. Controllers does not have responsoblity to save entities, they are only about web exchange. You can inject, for example, your @Repository or @Service component of A entity to your B controller and call a save() method for your entities. (better approach, in my opinion, will be to inject AResporitory inside BService class)

   UPDATED

   Example:

   @Transactional
   @Service
   public class LineaService {
   
   @Autowired
   private LineaRepository lineaRepo;
   @Autowired
   private MarcaService marcaService;
   
   public Linea create(Linea linea) {
       //creates new marca if not exists
       //no need for this block if you add cascade insert to your entity
       if (linea.getMarca().getId() == null) {
           marcaService.create(linea.getMarca());
       }
   
       return lineaRepo.save(linea);
   }
   

   If you set an existing marca value, you found it before, so in that case it's Id will have some value (user chose it on UI form, for example).

2. Another approach will be using cascade inserts in your B entitiy.

   @Entity
   public class EntityB {
   
       @ManyToOne(cascade = CascadeType.PERSIST)
       protected EntityA entityA;
   
   }
   

UPDATED Cascades does'nt create new rows of already existings, but Hibernate checks row's existence only by primary key. If your entity object has empty primary key it means that it is a new object and yout need to insert a new row. In many cases controller will recieve a filled marca's Id field, because as i wrote before, you user can select it on UI form using, for example, a some kind of "select component". But if in your case, user can't select a marca, and only can type it's name, then, of course, cascades won't be a good solution and u can search marca by nome firstly (as you do in your code).