Relevant knowledge of DRF

1.default_permissions = (), Clear the four default permissions , Namely add model, change model and delete model.

 2.

on_delete = None：
When deleting the data of the associated table , Current table and associated table filed act .
 on_delete = models.CASCADE：
Indicates cascade delete , When associated table （ Sub table ） When deleting data in , The corresponding foreign key （ Parent table ） Also delete the data in .
on_delete = models.DO_NOTHING:
You delete your , father （ Foreign keys ） I don't want to care about you
on_delete = models.PROTECT:
Protected mode , If this method is adopted , When the associated data is deleted, an ProtectError error
(5)、on_delete = models.SET_DEFAULT:
Set the default value , When deleting sub table fields , The foreign key field is set to the default value , So when defining a foreign key, you should add a default value .
(6)、on_delete = models.SET（ value ）:
When deleting associated data , Customize a value , The value can only correspond to the specified entity
3.order_by Usage of
Test.objects.all().order_by('id')   Ascending   From small to large

Test.objects.all().order_by('-id')   Descending   From big to small