Admin generic inlines for multi-table subclassed models broken --- any alternatives?
Here's what I'm trying to do, and failing...
I have a File model which has a generic-relation to other objects:
class File(models.Model): content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey() file = models.FileField(upload_to='files/%Y/%m/%d') # etc....
I also want to have a sub-class of File to deal with the specific case of images to be displayed in-page, rather than downloaded:
class Image(File): file = models.ImageField(upload_to='files/%Y/%m/%d')
All of the above works fine, including generic inlines of the File model, until I want to use a generic-inline of the Image model --- the save process fails to create the base class instance and so raises an error stating that the Image.file_ptr (the 'secret' foreign key to the base class) cannot be None.
So, basically, generic inlines do not properly support multi-table inheritance at the moment.
It's quite likely that I'm making this more complicated than it need be, so can anyone suggest either a fix for this problem, or a better way of achieving the same end?
Please let me know if you need further clarification.
Asked by: Arthur846 | Posted: 01-10-2021
Inheritance can be implemented two ways in a relational model.
A subclass can be a new table with all the same columns as the superclass repeated. This works well when you have an abstract superclass or subclass features that override the superclass.
A subclass can be just the unique columns with a join to the superclass table. This works well when you have a concrete superclass.
In your case, it looks you might have the following.
class FileFacts( models.Model ): content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey() class DownloadFile( models.Model ): facts = models.ForeignKey( FileFacts ) file = models.FileField(upload_to='files/%Y/%m/%d') class InlineImage( models.Model ): facts = models.ForeignKey( FileFacts ) file = models.ImageField(upload_to='files/%Y/%m/%d')
This is my preference for handling a subclass-like model.Answered by: Brad472 | Posted: 02-11-2021
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