Cascade

SQL Server: drop table cascade equivalent?

由 拟墨画扇 提交于 2019-11-26 09:46:00
问题 In oracle, to drop all tables and constraints you would type something like DROP TABLE myTable CASCADE CONSTRAINTS PURGE; and this would completely delete the tables and their dependencies. What\'s the SQL server equivalent?? 回答1: I don't believe SQL has a similarly elegant solution. You have to drop any related constraints first before you can drop the table. Fortunately, this is all stored in the information schema and you can access that to get your whack list. This blog post should be

How to show related items using DeleteView in Django?

由 依然范特西╮ 提交于 2019-11-26 09:37:55
问题 I am doing a view to delete (using the generic view DeleteView from Django) an instance from a model, but it cascades and deletes instances from other models: url(r\'^person/(?P<pk>\\d+)/delete/$\', login_required(DeleteView.as_view(model=Person, success_url=\'/person/\', template_name=\'delete.html\')), name=\'person_delete\'), What I want to do is to show the list of related items that are going to be deleted, as the admin interface does, like: Are you sure you are going to delete Person

What is the difference between cascade & inverse in hibernate, what are they used for?

由 喜欢而已 提交于 2019-11-26 08:55:18
问题 How to use cascade and inverse in hibernate? What is the procedure/tag to define them? Are they related to each other and how are they useful? 回答1: In case of many-to-many relation through intermediary table; "Cascade" says whether a record will be created/updated in the child table. Whereas "Inverse" says whether a record will be created/updated in the intermediary table e.g. Assume below scenario 1 student can have multiple phones. So Student class has property for Set of phones. Also 1

How to add “on delete cascade” constraints?

由 瘦欲@ 提交于 2019-11-26 07:59:40
问题 In PostgreSQL 8 is it possible to add ON DELETE CASCADES to the both foreign keys in the following table without dropping the latter? # \\d scores Table \"public.scores\" Column | Type | Modifiers ---------+-----------------------+----------- id | character varying(32) | gid | integer | money | integer | not null quit | boolean | last_ip | inet | Foreign-key constraints: \"scores_gid_fkey\" FOREIGN KEY (gid) REFERENCES games(gid) \"scores_id_fkey\" FOREIGN KEY (id) REFERENCES users(id) Both

JPA 2.0 orphanRemoval=true VS on delete Cascade

由 六月ゝ 毕业季﹏ 提交于 2019-11-26 04:04:19
问题 I am a little confused about the JPA 2.0 orphanRemoval attribute. I think I can see its is needed when I use my JPA provider\'s DB generation tools to create the underlying database DDL to have an ON DELETE CASCADE on the particular relation. However, if the DB exists and it already has an ON DELETE CASCADE on the relation, is this not enough to cascade the deletion appropriately? What does the orphanRemoval do in addition? Cheers 回答1: orphanRemoval has nothing to do with ON DELETE CASCADE .

How do I use on delete cascade in mysql?

由 微笑、不失礼 提交于 2019-11-26 02:12:00
问题 I have a database of components. Each component is of a specific type. That means there is a many-to-one relationship between a component and a type. When I delete a type, I would like to delete all the components which has a foreign key of that type. But if I\'m not mistaken, cascade delete will delete the type when the component is deleted. Is there any way to do what I described? 回答1: Here's what you'd include in your components table. CREATE TABLE `components` ( `id` int(10) unsigned NOT

What is the meaning of the CascadeType.ALL for a @ManyToOne JPA association

由 心已入冬 提交于 2019-11-26 00:57:02
问题 I think I misunderstood the meaning of cascading in the context of a @ManyToOne relationship. The case: public class User { @OneToMany(fetch = FetchType.EAGER) protected Set<Address> userAddresses; } public class Address { @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL) protected User addressOwner; } What is the meaning of the cascade = CascadeType.ALL ? For example, if I delete a certain address from the database, how does the fact that I added the cascade = CascadeType.ALL

What is the meaning of the CascadeType.ALL for a @ManyToOne JPA association

由 余生长醉 提交于 2019-11-25 23:42:16
I think I misunderstood the meaning of cascading in the context of a @ManyToOne relationship. The case: public class User { @OneToMany(fetch = FetchType.EAGER) protected Set<Address> userAddresses; } public class Address { @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL) protected User addressOwner; } What is the meaning of the cascade = CascadeType.ALL ? For example, if I delete a certain address from the database, how does the fact that I added the cascade = CascadeType.ALL affect my data (the User , I guess)? The meaning of CascadeType.ALL is that the persistence will propagate

MySQL外键约束

由 谁都会走 提交于 2019-11-25 20:37:26
CASCADE ：父表delete、update的时候，子表会delete、update掉关联记录； SET NULL ：父表delete、update的时候，子表会将关联记录的外键字段所在列设为null，所以注意在设计子表时外键不能设为not null； RESTRICT ：如果想要删除父表的记录时，而在子表中有关联该父表的记录，则不允许删除父表中的记录； NO ACTION ：同 RESTRICT，也是首先先检查外键； 来源： oschina 链接： https://my.oschina.net/depeng414/blog/3133606
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