Spring Boot Data JPA 中的自加入 - 仅显示第一个子节点（第 0 个元素）而不是所有子节点

Question

我想在应用程序中使用的用例是我有一个列表，列表将有很多孩子，孩子们会有孩子等等。 请参考下图。

为了实现这种层次结构，我创建了以下 Java 类；

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@Entity
@JsonNaming(value = PropertyNamingStrategy.SnakeCaseStrategy.class)
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"}) 
@EqualsAndHashCode(onlyExplicitlyIncluded = true)
@Table(name = "ITEM")
public class Item implements Serializable {

    private static final long serialVersionUID = 1L;
    
    @Id
    @JsonIgnore
    @Column(name = "ID", updatable = false, nullable = false, unique = true)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    
    @Size(max = 500)
    @Column(name = "TYPE", nullable = false, length = 500)
    private String type;
    
    @Column(name = "READONLY")
    private Boolean readOnly;
    
    @JsonBackReference
    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    @JoinColumn(name = "PARENT")
    private Item parent;
    
    @JsonManagedReference
    @Builder.Default
    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, orphanRemoval=true, fetch = FetchType.LAZY)
    private Set<Item> children = new HashSet<Item>();

}

插入工作正常。 但是当我检索数据时，我没有在Set<Item> children节点中获取父节点下的所有子节点，而是只获取第一个子节点，即； 集合中的第 0 个元素。 我不知道这里的问题，我做错了什么。 我得到如下输出；

  "items": [
    {
      "id": "1",
      "type": "PARENT 1",
      "parent": null,
      "readOnly": false,
      "children": [
        {
          "id": "6",
          "type": "CHILDREN 1",
          "parent": 1,
          "readOnly": false,
          "children": []
        }
      ]
    },
    {
      "id": "2",
      "type": " PARENT 2",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "3",
      "type": " PARENT 3",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "4",
      "type": " PARENT 4",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "5",
      "type": " PARENT 5",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "6",
      "type": "CHILDREN 1",
      "parent": 1,
      "readOnly": false,
      "children": []
    },
    {
      "id": "7",
      "type": "CHILDREN 1",
      "parent": 1,
      "readOnly": false,
      "children": []
    }
  ]
}

我应该在哪里得到这样的输出；

  "items": [
    {
      "id": "1",
      "type": "PARENT 1",
      "parent": null,
      "readOnly": false,
      "children": [
        {
          "id": "6",
          "type": "CHILDREN 1",
          "parent": 1,
          "readOnly": false,
          "children": []
        },
        {
          "id": "7",
          "type": "CHILDREN 1",
          "parent": 1,
          "readOnly": false,
          "children": []
        }
      ]
    },
    {
      "id": "2",
      "type": " PARENT 2",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "3",
      "type": " PARENT 3",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "4",
      "type": " PARENT 4",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "5",
      "type": " PARENT 5",
      "parent": null,
      "readOnly": false,
      "children": []
    },
    {
      "id": "6",
      "type": "CHILDREN 1",
      "parent": 1,
      "readOnly": false,
      "children": []
    },
    {
      "id": "7",
      "type": "CHILDREN 1",
      "parent": 1,
      "readOnly": false,
      "children": []
    }
  ]
}

在第一项中，我应该得到 2 个孩子，而是得到一个孩子元素。

Answer 1

您的问题可能与Item类的equals实现有关：您正在使用@EqualsAndHashCode(onlyExplicitlyIncluded = true)指示 Lombok 仅包含您希望在equals实现中的字段或方法，但您没有使用@EqualsAndHashCode.Include 。 请参阅相关文档。

由于这个原因，Lombok 可能正在生成一个equals实现，它起源于每个Item被认为与另一个相等，因此children Set只包含有关添加的第一个Item信息。

请使用@EqualsAndHashCode.Include注释您认为合适的字段，我认为它可以解决问题。 例如：

//...
@EqualsAndHashCode.Include
private Long id;