Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you about the role of on_delete parameters in Model foreign keys. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.

Parameter introduction models.CASCADE

Cascaded deletion. Django simulates the behavior of SQL constraints, and when deleting this piece of data, colleagues delete objects associated with foreign keys. For example, if a user has a foreign key associated with the user's health record table, when the user deletes, the data related to the user in the health record table configured with this parameter will also be deleted.



Reminder: cascading deletion will not call model-level behavior, but will send pre_delete and post_delete signals for all deleted objects. If you use Django's signaling mechanism, you should consider the impact of this cascade deletion.

"models.PROTECT

Prevents referenced objects from being deleted. On the contrary, it prevents the associated data from being deleted.

Models.SET_NULL

Set the associated foreign key content to null. Available only if null=True is set. When the data is deleted, the associated foreign key content is set to null.

Models.SET_DEFAULT

Set the value of the foreign key to the default value. Foreign keys must be set to a default value.

Models.SET () takes the value set by SET () as the value of the foreign key and, if callable is passed, calls its result.

DO_NOTHING does not take action. If the back-end database has a mandatory association operation, it is easy to report an error: IntegrityError, unless you manually add SQL's ON DELETE constraint to the database.

The above is the role of the on_delete parameter in the Model foreign key shared by the editor. If you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.