为什么json不显示列表中的对象？

Question

我正在做一个小宠物项目，无法解决这种情况。简单地说，我有 2 张表，一张是 ToDoBlock，另一张是 ToDo，关系为 OneToMany。因此，我在 Idea 的 httpClient 中使用 Post 创建了 ToDoBlock，然后使用另一个 POST 添加了 ToDo，但是当我使用 GET 调用我的 ToDoBlocks 时，它没有我的 ToDos 列表，它有但数组为空。

JSON 发布 ToDoBlock：

POST http://localhost:8080/todos/create-todo-block
Content-Type: application/json

{
 "name" : "block2"
}

JSON 后待办事项：

POST http://localhost:8080/todos/create-simple-todo/1
Content-Type: application/json

{
 "text" : "my third todo"
}

JSON GET all-blocks：（它工作正常）

GET http://localhost:8080/todos/get-all-blocks
Content-Type: application/json

JSON 获取所有待办事项：

GET http://localhost:8080/todos/find-all-todos
Content-Type: application/json

控制器：

@PostMapping(value = "/create-todo-block")
@ResponseStatus(HttpStatus.CREATED)
public void createToDoBlock(@RequestBody ToDoBlock toDoBlock){
    toDoService.saveToDoBlock(toDoBlock);
}

@PostMapping(value = "/create-simple-todo/{blockId}")
@ResponseStatus(HttpStatus.CREATED)
public void createToDo(@PathVariable long blockId, @RequestBody String text){
    toDoService.saveSimpleToDo(text, blockId);
}

道：

@Override
public void saveToDoBlock(ToDoBlock toDoBlock) {
    entityManager.persist(toDoBlock);
}

@Override
public void saveSimpleToDoByBlockId(String text, long blockId) {
    ToDo toDo = new ToDo(text);
    ToDoBlock block = entityManager.getReference(ToDoBlock.class, blockId);
    block.addToDo(toDo);
    entityManager.persist(block);
}

邮递员的回应：

[
{
    "id": 1,
    "name": "block",
    "archive": null,
    "toDos": []
}

]

实体待办事项：

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@EqualsAndHashCode(of = "id")
@Entity
@Table(name = "todo")
public class ToDo {

@Id
@GeneratedValue
private Long id;

@Column (nullable = false)
private String text;

@Column
private Scaryness scaryness;

@Column
private Hardness hardness;

@Column
private boolean ready;

@Column
private LocalDateTime createdOn;

@ManyToOne
@JoinColumn(name = "todo_block_id")
private ToDoBlock toDoBlock;

public ToDo(String text, ToDoBlock todoBlock) {
    this.text = text;
    this.toDoBlock = todoBlock;
    this.ready = false;
    this.createdOn = LocalDateTime.now();
}

}

实体 ToDoBlock：

@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode(of = "id")
@Setter
@Getter
@Entity
@Table(name = "todo_block")
public class ToDoBlock {

@Id
@GeneratedValue
private Long id;

@Column(name = "name")
private String name;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "archive_id")
private Archive archive;

@Setter(AccessLevel.PRIVATE)
@OneToMany(mappedBy = "toDoBlock")
private List<ToDo> toDos = new ArrayList<>();

public void addToDo(ToDo toDo){
    toDos.add(toDo);
    toDo.setToDoBlock(this);
}

public void removeToDo(ToDo toDo){
    toDos.remove(toDo);
    toDo.setToDoBlock(null);
}

}

Answer 1

请在https://github.com/ygor-sk/stackoverflow/tree/master/q53224496-many-to-one-not-in-json查看我的解决方案

关键是显式保存新的 ToDo 实体。将其添加到 ToDoBlock 中的集合是不够的。

public void saveSimpleToDoByBlockId(String text, long blockId) {
    ToDoBlock block = entityManager.getReference(ToDoBlock.class, blockId);
    ToDo toDo = new ToDo(text, block);
    block.addToDo(toDo);
    entityManager.persist(toDo); // <----- persist ToDo too
    entityManager.persist(block);
}

另一种可能性是定义级联，如下所述：JPA Updating Bidirectional Association

此外，我必须使用 @JsonIgnore 注释来注释从 ToDo 到 ToDoBlock 的引用。否则，我在序列化为 JSON 期间遇到了 stackoverflow 异常。

@JsonIgnore
@ManyToOne
@JoinColumn(name = "todo_block_id")
private ToDoBlock toDoBlock;