You can use the Collector class Django uses to determine what objects to delete in the cascade. Instantiate it and then call collect on it passing the objects you intend to delete. It expects a list or queryset, so if you only have one object, just put in inside a list: from django.db.models.deletion import Collector … Read more
ON DELETE CASCADE is fine, but only when the dependent rows are really a logical extension of the row being deleted. For example, it’s OK for DELETE ORDERS to delete the associated ORDER_LINES because clearly you want to delete this order, which consists of a header and some lines. On the other hand, DELETE CUSTOMER … Read more
Answer d. is correct, if and only if the storage engine actually supports and enforces foreign key constraints. If the tables are created with Engine=MyISAM, then neither b. or d. is correct. If the tables are created with Engine=InnoDB, then d. is correct. NOTE: This is true for InnoDB if and only if FOREIGN_KEY_CHECKS = … Read more
Cascade will work when you delete something on table Courses. Any record on table BookCourses that has reference to table Courses will be deleted automatically. But when you try to delete on table BookCourses only the table itself is affected and not on the Courses follow-up question: why do you have CourseID on table Category? … Read more
In SQL Server Management Studio, go to Options / SQL Server Object Explorer / Scripting, and enable ‘Generate script for dependent objects’. Then right click the table, script > drop to > new query window and it will generate it for you.
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 Phone … Read more
I’m pretty sure you can’t simply add on delete cascade to an existing foreign key constraint. You have to drop the constraint first, then add the correct version. In standard SQL, I believe the easiest way to do this is to start a transaction, drop the foreign key, add a foreign key with on delete … Read more
Summary of what I’ve seen so far: Some people don’t like cascading at all. Cascade Delete Cascade Delete may make sense when the semantics of the relationship can involve an exclusive “is part of” description. For example, an OrderLine record is part of its parent order, and OrderLines will never be shared between multiple orders. … Read more
Here’s what you’d include in your components table. CREATE TABLE `components` ( `id` int(10) unsigned NOT NULL auto_increment, `typeId` int(10) unsigned NOT NULL, `moreInfo` VARCHAR(32), — etc PRIMARY KEY (`id`), KEY `type` (`typeId`) CONSTRAINT `myForeignKey` FOREIGN KEY (`typeId`) REFERENCES `types` (`id`) ON DELETE CASCADE ON UPDATE CASCADE ) Just remember that you need to use … Read more
orphanRemoval has nothing to do with ON DELETE CASCADE. orphanRemoval is an entirely ORM-specific thing. It marks “child” entity to be removed when it’s no longer referenced from the “parent” entity, e.g. when you remove the child entity from the corresponding collection of the parent entity. ON DELETE CASCADE is a database-specific thing, it deletes … Read more