@OnDelete休眠注释不会为MySql生成ON DELETE CASCADE

问题描述

我有两个具有单向关系的父级和子级

I have two entities parent and child with a unidirectional relationship

class Parent {
    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    private Long id;
}

和

class Child {
    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    private Long id;

    @ManyToOne(optional = false)
    @JoinColumn(name = "parent_id")
    @OnDelete(action = OnDeleteAction.CASCADE)
    private Parent parent;
}

在我配置的application.properties文件中

In the application.properties file I have configured

spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.database-platform = org.hibernate.dialect.MySQL5InnoDBDialect

但是当我运行应用程序时，将创建以下语句

But when I run the application the following statement is created

...
alter table child add constraint FKi62eg01ijyk2kya7eil2gafmx foreign key (parent_id) references parent (id)
...

因此，没有应有的ON CASCADE DELETE.每次我运行应用程序并检查方法是否创建表时都会

So there is no ON CASCADE DELETE as there should be. The tables are created each time I run the application and I checked if the method

org.hibernate.dialect.MySQL5InnoDBDialect#supportsCascadeDelete()

真的被称为(是).我正在使用spring-boot-parent版本1.4.3，该版本使用Hibernate 5.11.有任何想法吗?我不想顺便使用双向关系.

is really called (it is). I am using spring-boot-parent version 1.4.3, which uses Hibernate 5.11. Any ideas? I do not want to use a bi-directional relationship by the way.

修改感谢@AlanHay，我发现我省略了重要的部分.实际上涉及到三等班

EditThanks to @AlanHay I discovered that I omitted an important part. There actually is a third class involved

class Kindergarten {

    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    private Long id;

    @OneToMany(mappedBy = "kindergarten", fetch = FetchType.EAGER)
    @MapKeyJoinColumn(name = "parent_id") // parent_id causes the problem!
    private Map<Parent, Child> children;
}

带幼儿园的孩子看起来像这样

and Child with Kindergarten looks actually like this

class Child {

    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    private Long id;

    @ManyToOne(optional = false)
    @JoinColumn(name = "parent_id")
    @OnDelete(action = OnDeleteAction.CASCADE)
    private Parent parent;

    @ManyToOne
    @JoinColumn(name = "kindergarten_id")
    private Kindergarten kindergarten;
}

，这就是问题发生的原因.如果您将MapKeyJoinColumn批注中的"parent_id"更改为Child作为列中不存在的内容，例如将ON DELETE CASCADE的"map_id"添加到Child的外键parent_id中.如果参数是子级的"parent_id"列，则不会附加ON DELETE CASCADE部分.不幸的是，原因尚不清楚.更改参数是没有选择的，因为我想使用到子对象的父对象的现有链接.

and that is why the problem occurs. If you change "parent_id" in the MapKeyJoinColumn annotation to something not existing in Child as a column e.g. "map_id" the ON DELETE CASCADE is added to the foreign key parent_id in Child. If the parameter is the Child's column "parent_id" the ON DELETE CASCADE part will not be appended. Unfortunately the reason for this is not yet clear to me. Changing the parameter is no option because I want to use the existing link to parent of the child object.

推荐答案

也许有点晚，但由于它是搜索休眠ondelete生成级联"时的热门文章之一:

Maybe a little late, but since it is one of the top posts when searching for 'hibernate ondelete generate cascade':

由于某种原因，将@OnDelete放在Mysql的ManyToOne端对我不起作用，但它在OneToMany端起作用.因此，如果您不走运，请尝试另一面.

For some reason putting @OnDelete on the ManyToOne side in Mysql did not work for me, but it worked on the OneToMany side. So if you are unlucky, try it on the other side.

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