Why on_delete of Django Rest Framework not work as expected on Image and File Fields?-CodePudding

When I delete the parent table using Django rest due to on_delete it deletes the child table also (due to foreign key) but the Image and File content of the child table not deleted. I want to delete those images and Files also..! How to do that..?

My tables 1:Group 2:Posts One To Many Relation

I delete the Group table as follows:

GroupsModel.objects.filter(id=py_data.get('group_id')).delete()

GroupsModel :

class GroupsModel(models.Model):
    group_name = models.CharField(max_length=20, unique=True)
    group_description = models.CharField(max_length=50)
    group_joining_link = models.CharField(max_length=50, default='', unique=True)
    user_id = models.ManyToManyField(UserModel, through='UserModelGroupsModel', related_name='u_g')

    class Meta:
        db_table = 'groups'

GroupPostsModel:

class GroupPostsModel(models.Model):
    post_text = models.CharField(max_length=1000)
    post_type = models.CharField(max_length=20)
    image = models.ImageField(blank=True, null=True, upload_to='post_images/')
    document = models.FileField(blank=True,null=True, upload_to='post_documents/')
    likes = models.IntegerField(default=0)
    time_stamp = models.DateTimeField(auto_now=True)
    group = models.ForeignKey(GroupsModel, on_delete=models.CASCADE)
    user = models.ForeignKey(UserModel, on_delete=models.CASCADE)

    class Meta:
        db_table = 'group_posts'

I want to delete image and document file also automatically.

CodePudding user response：

When an instance is removed referred files are not deleted, since the ImageField/FileField is only a reference to the files. You can override the delete method of your model:

import os

class GroupPostsModel(models.Model):
    post_text = models.CharField(max_length=1000)
    post_type = models.CharField(max_length=20)
    image = models.ImageField(blank=True, null=True, upload_to='post_images/')
    document = models.FileField(blank=True,null=True, upload_to='post_documents/')
    likes = models.IntegerField(default=0)
    time_stamp = models.DateTimeField(auto_now=True)
    group = models.ForeignKey(GroupsModel, on_delete=models.CASCADE)
    user = models.ForeignKey(UserModel, on_delete=models.CASCADE)
    
    def delete(self):
       if self.image:
          if os.path.isfile(self.image.path):
             os.remove(self.image.path)

       if self.document:
          if os.path.isfile(self.document.path):
             os.remove(self.document.path)
       
       super().delete()

    class Meta:
        db_table = 'group_posts'

The delete method will not be called in the queryset you wrote, you need to delete each instance individually:

for instance in GroupsModel.objects.filter(id=py_data.get('group_id')):
   instance.delete()

CodePudding user response：

on_delete=models.CASCADE on a ForeignKey is something written and managed on the database schema. It is not Django that delete the child model on delete, but your database (MySQL, Postgres, ...) that automaticaly detect a failure on ForeignKey and perform a Cascade action (like a contraint).

models.ImageField and models.FileField are (at database level) just a CharField with the location on the file system of your file. The database cannot remove a file, so you cannot delegate this action to the database.

If you want automatic removal of file on Model .delete(), you have multiple possible strategy :

Periodic check that for each file, a model exists (if not, remove the file)
Overwrite the .delete() method of GroupPostsModel (but it will only work if you call .delete() on an instance of the model, not on a queryset, like on your exemple)
Add the removal feature on the delete endpoint.