Question

I’m getting stuck on a complex query, trying to use Django’s ORM.

models.py

class Product(models.Model):
    deprecated = models.ForeignKey(SpecialVersion, null=True)

class Version(models.Model):
    compatible_from = models.ForeignKey(SpecialVersion)
    product = models.ForeignKey(Product)

class SpecialVersion(models.Model):
    version = models.ForeignKey(Version, null=True)
    order = models.IntegerField()

The gist of this is, Products have multiple Versions. Some of these Versions are ‘special’ – we keep track of this by making a SpecialVersion object pointing to the ‘special’ Version object. When we create a non-special version, it must indicate a compatibility with a SpecialVersion. That is, starting at the SpecialVersion indicated by compatible_from. A Product can become deprecated at a certain special version.

Now, I want to be able to find appropriate Products given a certain SpecialVersion. In other words, I want to get all Product objects where there is a Version available that has a SpecialVersion below my given SpecialVersion. Furthermore, the Product’s deprecated SpecialVersion must be either null, or below the given SpecialVersion if not null.

TL;DR:
Select all Products where the given SpecialVersion is in the range between the lowest compatible_from SpecialVersion in the product, and the deprecated SpecialVersion (if this exists).

EDIT: Example.

Products
id | deprecated
0 | None
1 | 2

Versions
id | prd | compat
0 | 0 | 1
1 | 0 | 2
2 | 1 | 2

SpecialVersions
id | ver | ord
0 | Null | 1
1 | Null | 2
2 | Null | 3
3 | Null | 4

A query for compatibility w/ SpecialVersion would return no products, because none of the products have versions that specify a compatibility as low as that. A query for compat w/ SpecialVersion would return all of the Products because they both have compatibility starting at SpecialVersion id=1 and id=2, respectively. Finally, a query for compat w/ SpecialVersion would return ONLY the product id=0 because though both products have a SpecialVersion compat low enough, the second product has been deprecated for SpecialVersions and upwards.

Answer 1

Here is what I ended up using:

products = Product.objects.annotate(min_version=Min(version_set__compatible_from__order)).filter(min_version__lte = given_special_version).filter(Q(deprecated__isnull = True) | Q(deprecated__order__gt = given_special_version))