java JPA：删除的外键约束
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JPA: Foreign key constraint on delete
提问by shazinltc
I have the following relationship
我有以下关系
Class UserAccount{
//Other fields
@OneToMany(mappedBy = "userAccount", cascade = CascadeType.REMOVE)
private Set<Images> imagesShared;
@ManyToMany
@JoinTable(name = "USER_LIKES", joinColumns = @JoinColumn(name = "USER_NAME"), inverseJoinColumns = @JoinColumn(name = "ID"))
private Set<Images> imagesLiked;
}
Class Images{
//other fields
@ManyToMany(mappedBy = "imagesLiked")
private Set<UserAccount> likes;
}
I get an exception after these lines
在这些行之后我得到一个例外
Hibernate: delete from IMAGES where ID=?
Hibernate: delete from COMMENTS where COMMENT_ID=?
Hibernate: delete from COMMENTS where COMMENT_ID=?
Hibernate: delete from COMMENTS where COMMENT_ID=?
Hibernate: delete from COMMENTS where COMMENT_ID=?
Hibernate: delete from COMMENTS where COMMENT_ID=?
Hibernate: delete from IMAGES where ID=?
Exception:
例外：
Cannot delete or update a parent row: a foreign key constraint fails (`testdb`.`USER_LIKES`, CONSTRAINT `FKC6704E28B4E3D8B` FOREIGN KEY (`ID`) REFERENCES `IMAGES` (`ID`))
From my understanding this happens when JPA tries to remove imagesShared.
I tried doing this:
据我了解，当 JPA 尝试删除imagesShared. 我试过这样做：
for (Images image : userAccount.getImagesShared()){
image.setLikes(null);
}
em.remove(account);
But same error. Anyone?
但同样的错误。任何人？
UPDATE
更新
When I add this line it works fine.
当我添加这一行时，它工作正常。
for (Images image : userAccount.getImagesShared()){
image.setLikes(null);
}
userAccount.getImagesShared().clear();
em.remove(account);
But what is the difference between the remove operation that JPA does and what I do?
但是JPA做的remove操作和我做的有什么区别呢？
回答by Thihara
One of your private Set<Images> imagesSharedor private Set<Images> imagesLikedmust have a reference to the Image you are trying to delete.
您的一个private Set<Images> imagesShared或private Set<Images> imagesLiked必须引用您要删除的图像。
You will have to loop through everything and remove the image reference before removing it.
在删除之前，您必须遍历所有内容并删除图像参考。
EDIT :
编辑 ：
To answer your second question.
回答你的第二个问题。
for (Images image : userAccount.getImagesShared()){
image.setLikes(null);
}
userAccount.getImagesShared().clear();
em.remove(account);
works because you are clearing the image references stored in userAccountby calling userAccount.getImagesShared().clear()
有效，因为您正在userAccount通过调用清除存储的图像引用userAccount.getImagesShared().clear()
Previously what you were doing was simply removing the likes stored in that Image, not removing the images from the userAccountobject itself.
以前您所做的只是删除存储在该图像中的喜欢，而不是从userAccount对象本身中删除图像。
回答by Lakshmi
The private Set<Images> imagesLikedhas a foreign key reference to the IMAGES(ID) so if you are trying to delete the private Set<Images> imagesShared;without deleting the private Set<Images> imagesLiked;.
Theprivate Set<Images> imagesLiked具有对IMAGES( ID)的外键引用， 因此如果您尝试删除private Set<Images> imagesShared;而不删除private Set<Images> imagesLiked;.
So try removing the imagesLinked also
所以也尝试删除 imagesLinked
image.setImagesLinked(null);
