使用 spring boot 和 spring 数据 jpa 时 OneToMany 关系的复杂行为

Question

I am developint simple Crud Application in Spring Boot with Data JPA, my goal is simple where I have two Entities: Foo.java

@Data // lombok annotation
@Entity(name = "foos")
public class Foo{

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(unique = true, nullable = false)
    private Integer fooId;

    private String FooName;

    @NonNull
    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "bar_id")
    private List<Bar> barList;

}

Bar.java

@Data
@Entity(name = "bars")
public class Bar{

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id", unique = true, nullable = false)
    private Integer barId;

    private String barTitle;

}

In my controller I want to save Foo with List of Bars as:

@Controller
@RequestMapping(value = "/foo")    
public class FooController {

    private final FooService fooService;
    private final BarService barService;

    public FooController(FooService fooService, BarService barService) {
        this.fooService = fooService;
        this.barService = barService;
    }

    @GetMapping(value = "/{id}/add_bar")
    public String addBar(@PathVariable("id") Integer id,  Model model){
        model.addAttribute("foo", fooService.findById(id));
        model.addAttribute("bar", new Bar());
        return "add_bar";
    }

    @PostMapping(value = "/{id}/add_bar")
    public String saveBar(
            @PathVariable("id") Integer id,
            @ModelAttribute("bar") Bar bar,
            BindingResult result
    ){
        if (result.hasErrors()) {
            return "add_bar";
        }
        // update foo by adding new bar and save
        Foo foo = getFooAndAddBar(id, bar);
        fooService.save(foo);
        // save bar
        barService.save(bar);

        return "redirect:/foo/" + foo.getFooId();
    }

    // update foo by adding new bar and save
    private Foo getFooAndAddBar(Integer id, Bar bar) {
        Foo foo = fooService.findById(id);
        ArrayList<Bar> barList = new ArrayList<>();
        barList.add(bar);
        foo.setBarList(barList);
        return foo;
    }
}

First bar is saved and fetched by foo id, but when ever I want to add another bar it only updates the first bar instead of inserting a new bar record in DB. is there any thing missing for @OneToMany association? or something is missing in other part of the program? please.

Answer 1

you are setting your barlist every time you are calling your function. You have written foo.setBarList(barList); . every time this will overwrite the previous barlist and then save it resulting in overwriting the previous values. Instead of this try this foo.getBarList().add(Bar) . It will fetch the previous list of bar and then will add new bar to the list. After this just save the entity