I asked a while back about having generic relations and someone pointed
me to
http://docs.djangoproject.com/en/1.2/ref/contrib/contenttypes/#generic-relations
This wasn't what I was looking for.
What I was looking for is this model I made:
class Relationship(models.Model):
id = fields.UUID(auto_add=True,primary_key=True, unique=True)
created_by = fields.UUID(db_index=True,null=True,blank=True)
created_on = models.DateField(auto_now=False,auto_now_add=True)
modfied_on = models.DateField(auto_now=True,auto_now_add=False)
title = models.CharField(max_length=255)
source_id = fields.UUID(db_index=True)
source_app_label = models.CharField(db_index=True,max_length=255)
source_model = models.CharField(db_index=True,max_length=255)
destination_id = fields.UUID(db_index=True)
destination_app_label = models.CharField(db_index=True,max_length=255)
destination_model = models.CharField(db_index=True,max_length=255)
description = models.TextField(null=True,blank=True)
type =
models.CharField(max_length=64,null=True,blank=True,db_index=True)
priority = models.PositiveIntegerField()
Then an abstract model that all my "digital assets (ie: images,
articles, comments, audio files, video files, etc)" extend contain these
methods:
def getType(self):
if (self._type == None):
self._type = ContentType.objects.get_for_model(self)
return self._type
def relatedTo(self):
rels = Relationship.objects
return
rels.filter(source_app_label=self.getType().app_label).filter(source_model=self.getType().model).filter(source_id=self.id)
def addRelation(self,destModel,type=None,priority=0):
rel = Relationship()
rel.destination_app_label = destModel._getType().app_label
rel.destination_model = destModel.getType().model
rel.destination_id = destModel.id
rel.source_app_label = self.getType().app_label
rel.source_model = self.getType().model
rel.source_id = self.id
rel.type = type
rel.priority = priority
rel.save()
This APPEARS to do what I want it to do:
1) it describes the relationship with some meta data
2) it allows me to use filters to find relationships
3) it's not a constraint, so no cascading deletes
4) it's many-to-many. Any asset can be related to any other asset. It
seems GenericForeignKey can do: "this tag is related to this bookmark",
but it can't do "this bookmark, this article, and this photo, have these
tags related to them"
However, I see problems:
1) It's a single point of failure!!
2) This is a db table that can grow very quickly
3) I lose other functionality, like being able to quickly get an
instance of the referenced object
So I wonder if anyone has any advice. I'm new to Python and don't fully
understand it's limitations, so I might not be thinking big enough (ie:
I could be having behind-the-scenes functionality that automatically
creates tables for relationships between specific model classes, but is
that performant?).
Perhaps even an existing open source project to handle these kinds of
relationships.
Thank you
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