Question

I am building a block system with a base block model with each type of block a separate subclass like so:

class BlockType(models.Model):
    ''' Defines properties of a block '''
    title = models.CharField(max_length=50)
    class_name = models.CharField(max_length=50)

class Block(models.Model):  
    ''' Implementation of the block '''
    product = models.ForeignKey('product.Product', related_name='blocks')
    block_type = models.ForeignKey('product.BlockType', related_name='used_blocks')
    order = models.IntegerField(default=0)

class ImageBlock(Block):
    ''' An image block '''
    image = models.CharField(max_length=255)

class TextBlock(Block):
    ''' A text block '''
    text = models.TextField()

What I’d like to be able to do is:

b = product.blocks.all()

And instead of this being a list of Block objects. Being a list of relevant subclasses.

So if a product had a TextBlock and 2 ImageBlocks. The above would have returned a TextBlock object and 2 ImageBlocks rather than 3 Block objects.

Answer 1

I’m affraid you can’t do that. But the question is: why you want to do that?

Before continuing, i have another question: Did you know that modeling these “blocks” the way you did you will get 3 different tables (4 with the “BlockType” table) in your database? Is that what you want?

I don’t know what you are going to do with these models and how you want to use them, so i will give you some links i think can help you a lot. If you want, you could give us more information about what you are going to do with these models and why you want to have a single queryset with two different models so we can really help you.

This could help you: https://docs.djangoproject.com/en/dev/topics/db/models/#proxy-models

or this: https://docs.djangoproject.com/en/dev/topics/db/models/#abstract-base-classes

Hope it helps! If no, please add more info in order to help us understand your problem and try to give you an answer