问题描述
我有一些由Hibernate管理的表，具有各种外键约束。级联删除目前仅由Hibernate管理。为了玩弄测试数据，我经常手动创建和删除一些行。如果我可以将ON DELETE CASCADE添加到外键约束中，它会帮助我很多，但我不知道Hibernate是否会因此而绊倒这个数据库，因为数据库在Hibernate之前将其删除。
很多人似乎都专注于DDL。我的意图是 not 指示Hibernate使用SQL DELETE CASCADES创建DDL。我只想知道，如果我在数据库中另外指定ON DELETE CASCADE以使JPA的 cascade = CascadeType.REMOVE 在引用注释中，例如 @ManyToOne 。
使用 CascadeType.DELETE ，但是这个注解只适用于 EntityManager 中的对象，而不是数据库。您要确保将 ON DELETE CASCADE 添加到数据库约束中。要验证，您可以配置JPA生成一个ddl文件。看看 ddl 文件，你会注意到 ON DELETE CASCADE 不是约束的一部分。将 ON DELETE CASCADE 添加到 ddl 文件中的实际SQL，然后从ddl更新数据库模式。这将解决您的问题。
显示了如何在 CONSTRAINT ON DELETE CASCADE 在MySQL中。你在约束上做到这一点。您还可以在 CREATE TABLE 或 ALTER TABLE 语句中执行此操作。 JPA很可能在 ALTER TABLE 语句中创建约束。只需在该语句中添加 ON DELETE CASCADE 即可。
Hibernate确实使用 @OnDelete 注释来提供这个功能，所以最好使用这个或者直接更新ddl文件，如果你想坚持标准的JPA功能。
I have some tables managed by Hibernate with various foreign key constraints. Cascade on delete is currently managed by Hibernate alone. For playing around with test data I often create and remove some rows by hand. It would help me a lot if I could add ON DELETE CASCADE to the foreign key constraints but I don't know if Hibernate trips over this because the database removes stuff before Hibernate does.
A lot of people seem to concentrate on DDL. My intention is not to instruct Hibernate to create DDL with SQL DELETE CASCADES. I just want to know if it does any harm if I specify an ON DELETE CASCADE in the database in addition to having JPA's cascade = CascadeType.REMOVE on the reference annotation, e.g., @ManyToOne.
You can use CascadeType.DELETE, however this annotation only applies to the objects in the EntityManager, not the database. You want to be sure that ON DELETE CASCADE is added to the database constraint. To verify, you can configure JPA to generate a ddl file. Take a look at the ddl file, you'll notice that ON DELETE CASCADE is not part of the constraint. Add ON DELETE CASCADE to actual SQL in the ddl file, then update your database schema from the ddl. This will fix your problem .
This link shows how to use ON DELETE CASCADE on for CONSTRAINT in MySQL. You do this on the constraint. You can also do it in a CREATE TABLE or ALTER TABLE statement. It's likely that JPA creates the constraint in an ALTER TABLE statement. Simply add ON DELETE CASCADE to that statement.
Note that some JPA implementors do provide a means for this functionality.
Hibernate does supply this functionality using the @OnDelete annotation, thus it is preferred to use this or simply update the ddl file if you would like to stick with standard JPA functionality.
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