HIbernate无法使用外键删除实体。外键设置为null

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此问题已在此处以多种形式提出，但这些解决方案似乎都不适用于我。我正在尝试删除父实体，我希望也删除所有子实体。

This question has been asked in many forms here but none of the solutions seem to work for me. I'm trying to delete the parent entity and I want all of the child entities to also be deleted.

我的实体：

@Entity @Table(name = "item", catalog = "myshchema") public class Item implements java.io.Serializable { @JoinColumn(name = "item_id", insertable = false, updatable = false, nullable = false) @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, orphanRemoval = true) private Set<ItemCategory> categories; /* Getters and Setters and other fields*/ }

项目表：

CREATE TABLE `item` ( `item_id` int(11) NOT NULL AUTO_INCREMENT, `store_id` int(11) NOT NULL, PRIMARY KEY (`item_id`), UNIQUE KEY `item_id_UNIQUE` (`item_id`), KEY `FK_ITEM_STORE_ID_idx` (`store_id`), CONSTRAINT `FK_ITEM_STORE_ID` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON DELETE NO ACTION ON UPDATE NO ACTION ) ENGINE=InnoDB AUTO_INCREMENT=84 DEFAULT CHARSET=utf8;

我的其他实体

@Entity @Table(name = "item_category", catalog = "myschema") @IdClass(ItemCategoryIndex.class) public class ItemCategory implements java.io.Serializable { @Id @Column(name = "category_id", unique = true, nullable = false, insertable = false, updatable = false) private Integer categoryId; @Id private Store store; @Id private Item item; @Id private String categoryName; /* Getters and Setters */ }

表for ItemCategory：

Table for ItemCategory:

CREATE TABLE `item_category` ( `category_id` int(11) NOT NULL AUTO_INCREMENT, `store_id` int(11) NOT NULL, `item_id` int(11) NOT NULL, `category_name` varchar(45) NOT NULL, PRIMARY KEY (`category_id`), UNIQUE KEY `category_id_UNIQUE` (`category_id`), UNIQUE KEY `IDX_UNIQUE_STORE_CATEGORY` (`store_id`,`item_id`,`category_name`) USING BTREE, KEY `FK_CATEGORY_STORE_ID_idx` (`store_id`), KEY `FK_ITEM_CATEGORY_ID_idx` (`item_id`), CONSTRAINT `FK_CATEGORY_STORE_ID` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `FK_ITEM_CATEGORY_ID` FOREIGN KEY (`item_id`) REFERENCES `item` (`item_id`) ON DELETE CASCADE ON UPDATE NO ACTION ) ENGINE=InnoDB AUTO_INCREMENT=162 DEFAULT CHARSET=utf8;

我尝试删除这样的项目：

I try to delete the item like this:

Item item = entityManager.find(Item.class, idList.get(i)); entityManager.remove(item);

我的日志显示Hibernate正在尝试将ItemCategory的主键设置为null：

My logs show that Hibernate is trying to set the primary key for ItemCategory to null:

Hibernate: update myschema.item_category set item_id=null where item_id=? ERROR o.h.e.jdbc.spi.SqlExceptionHelper.logExceptions 146 - Column 'item_id' cannot be null

我甚至尝试循环遍历子记录并手动删除它们，但Hibernate仍然将此更新发送到null查询。我做错了什么？

I even tried looping through the child records and deleting them manually, but Hibernate still issues this update to null query. What am I doing wrong?

推荐答案

我必须将你的问题分解为两部分 首先 - 让我们谈谈您的数据库架构设计。

根据您的架构， item 和 item_category 有一个一对多关系，这意味着一个项目可以拥有/被分配到不同的类别但是不同的项目不能具有/被分配到相同的类别。

I have to break your problem down to two parts First - let's talk about your database schema design.

According to your schema, item and item_category has a one-to-many relationship meaning an item can have/be-assigned-to different categories but different items cannot have/be-assigned-to the same category.

如果确实是你的业务要求那么是完全正常，我提到它是因为它对我没有意义，这种情况很少发生。

That is totally fine if it is indeed your business requirement, I mention it because it does not make sense to me and this circumstance rarely happens.

如果你想要的是一个类别可以有多个项目，反之亦然， item 和 item_category 必须是多对多关系。此外应该有一个连接表。

If what you want is that a category can have multiple items and vice versa, itemand item_category must be a many-to-many relationship. There should be a join table additionally.

ItemCategory 是该关系的所有者，因为它有一个外键 item_id 引用 item 表。所以ItemCategoy应该像这样粗略：

ItemCategory is the owner of the relationship because it has a foreign key item_id refering to item table. So the ItemCategoy should look roughly like this:

@Entity @Table(name = "item_category") public class ItemCategory { @Id private Integer categoryId; private Store store; @ManyToOne @JoinColumn(name="item_id", /*cascade = ...*/) private Item item; private String categoryName; /* Getters and Setters */ }

您的项目实体将粗略，如下所示：

Your Item entity will be roughly like this:

@Entity @Table(name = "item", catalog = "myshchema") public class Item implements java.io.Serializable { @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, orphanRemoval = true, mappedBy="item") private Set<ItemCategory> categories; //`mappedBy`used here because this entity is not the owner of the relationship according to what mentioned above /* Getters and Setters and other fields*/ }

从<$ c删除所有子实体（ ItemCategory ） $ c>项目，只需

To remove all the child entities(ItemCategory) from Item , simply

em.remove（item）;

orphanRemoval 是 true ，删除父母，子女也将被删除。

The orphanRemoval is true, deleting the parent, the children will be deleted as well.