java - Hibernate 为一对多域对象的每个创建查询插入两条记录

Question

我有一个 Category 域对象，旨在复制分类术语树。由于一些额外的引用映射，我有必要重写对象创建代码。现在的最终结果是，Hibernate 会在每次执行 create() 时将两条数据记录插入到数据库中。一个数据记录包含所有 NULL 值，而另一个包含预期数据。

我的类别对象:

@Entity
@NamedQuery(
    name="findCategoryByName",
    query="select category FROM Category c WHERE c.category = :category"
)
@Table(name = "categories")
public class Category implements Serializable{

    @Id
    @Column(name = "category_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @Column
    private String category;

    @ManyToMany(mappedBy = "categories", cascade = CascadeType.PERSIST)
    private List<Photo> photos= new ArrayList<>();;

    @ManyToOne(cascade = CascadeType.PERSIST)
    private Category parent;

    @OneToMany(mappedBy = "parent", cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
    private List<Category> categoryList = new ArrayList<>();

    public Category() { }

    public Category(String category){
        this.category = category;
    }

    /* Other getters and setters */

}

URL localhost:8080/admin/category/create 使用 POST 请求命中此 Controller 方法:

@RequestMapping(value = AdminRestURIConstants.CREATE_CATEGORY, method = RequestMethod.POST)
@ResponseStatus(HttpStatus.OK)
@ResponseBody
public Category createCategory(@RequestBody Category category){
    log.info("Start creating category " + category.getCategory());
    Category newCategory = categoryService.createCategory(category);
    return newCategory;
}

这是我用于数据插入的存储库覆盖方法:

/**
 *
 * @param category
 * @return
 *
 * A Category object can be created with two types of parent references.  An Integer means the parent reference
 * exists, and the new Category will be added to the existing child set.  A String means the parent reference
 * is non-existing, and so two Category objects are made and bound.
 *
 * To maintain compatibility with the field settings of the Category domain model, an Integer value is passed in as a
 * String, and the execution of a parent update or create is made upon the thrown NumberFormatException when string-to-int
 * conversion fails.
 */
@Override
public Category create(Category category){
    try {
        int parentId = Integer.parseInt(category.getParent().getCategory());

        Category parent = super.findOne(parentId);
        category.setParent(parent);

        if (parent != null){
            parent.addCategory(category);
            update(parent);
        }
        else {
            throw new NumberFormatException();
        }
    } catch (NumberFormatException e){

        Category newParent = new Category(category.getParent().getCategory());
        newParent.addCategory(newCategory);
        newCategory.setParent(newParent);

        super.create(newParent);
    }

    super.create(newCategory);
    delete(category);
    return newCategory;
}

截至目前，如果我传入父类别的 ID 以及一个字符串，新类别将添加到父类别 categoryList。但是，也插入了一个 NULL 记录:

{
    "id": 41,
    "category": "testCategory",
    "photos": null,
    "categoryList": [
        {
            "id": 42,
            "category": "newCategory",
            "photos": null,
            "categoryList": []
        },
        {
            "id": 83,
            "category": "newCategoryChild",
            "photos": null,
            "categoryList": []
        }
    ]
},
{
    "id": 42,
    "category": "newCategory",
    "photos": null,
    "categoryList": []
},
{
    "id": 82,
    "category": null,
    "photos": null,
    "categoryList": []
},
{
    "id": 83,
    "category": "newCategoryChild",
    "photos": null,
    "categoryList": []
}

如您所见，类别 newCategoryChild 在 testCategory 的 categoryList 数组中被引用。但是，在创建此记录之前，会创建一个空对象。这也在服务器日志中得到支持:

Hibernate: select category0_.category_id as category1_0_1_, category0_.category as category2_0_1_, category0_.parent_category_id as parent3_0_1_, categoryli1_.parent_category_id as parent3_0_3_, categoryli1_.category_id as category1_0_3_, categoryli1_.category_id as category1_0_0_, categoryli1_.category as category2_0_0_, categoryli1_.parent_category_id as parent3_0_0_ from categories category0_ left outer join categories categoryli1_ on category0_.category_id=categoryli1_.parent_category_id where category0_.category_id=?
Hibernate: select categoryli0_.parent_category_id as parent3_0_1_, categoryli0_.category_id as category1_0_1_, categoryli0_.category_id as category1_0_0_, categoryli0_.category as category2_0_0_, categoryli0_.parent_category_id as parent3_0_0_ from categories categoryli0_ where categoryli0_.parent_category_id=?
Hibernate: insert into categories (category, parent_category_id) values (?, ?)
Hibernate: insert into categories (category, parent_category_id) values (?, ?)

和数据库:

mysql> select * from categories;
+-------------+------------------+--------------------+
| category_id | category         | parent_category_id |
+-------------+------------------+--------------------+
|          41 | testCategory     |               NULL |
|          42 | newCategory      |                 41 |
|          88 | NULL             |               NULL |
|          89 | newCategoryChild |                 41 |
+-------------+------------------+--------------------+
4 rows in set (0.00 sec)

SO 上还有其他关于类似情况的帖子，但其中许多是未知的 merge 或 persist 调用的结果。我在整个数据插入过程中逐步完成了每个方法，唯一的 persist 或 merge 调用直接来自上面的存储库代码。

Answer 1

在您的存储库代码“public Category create(Category category){}”方法中，很明显如果 parent 为 NULL，它将抛出 new NumberFormatException()，稍后您在 catch block 中捕获异常并创建父级Category.After，您创建新的Category 对象。如你所见，你已经创建了两个对象，当parent为null时，它将创建(category NULL,parent_category_id NULL)。

需要指出的是，在你上面的方法中，没有newCategory的定义(我假设它是在你的类中声明的)并且最后一条语句“delete(category)”非常困惑。

我建议您仔细检查您的代码。