Annotate function give me a wrong result

Question

I have set the following three models in my django app:

class SubCategory(models.Model):
    name = models.CharField('Nome della sottocategoria', max_length=30)

class Materials(models.Model):
    subcategory= models.ForeignKey(SubCategory)
    quantity=models.DecimalField()
    price=models.DecimalField()

class Costs_materials(models.Model):
    subcategory= models.ForeignKey(SubCategory)
    quantity=models.DecimalField()

In my views I have set the following code:

agg=Subcategory.objects.annotate(giacenza=Coalesce(Sum('materials__quantity'), 0)).annotate(
        utilizzato=Coalesce(Sum('costs_materials__quantity'), 0))

All works perfectly but If I try to add another annotate function, ad example:

agg=Subcategory.objects.annotate(giacenza=Coalesce(Sum('materials__quantity'), 0)).annotate(
        utilizzato=Coalesce(Sum('costs_materials__quantity'), 0))

The result of giacenza and utilizzato are not right, but the result is double than the right. Ad example if the result must be 10, is 20.

Where is the error??

If you make use of two one-to-many relations, you make two `JOIN`s, hence these will act as a *multiplier* of each other. — Willem Van Onsem, Jul 12 '20 at 14:59
Does this answer your question? [Django Count and Sum annotations interfere with each other](https://stackoverflow.com/questions/56567841/django-count-and-sum-annotations-interfere-with-each-other) — iklinac, Jul 12 '20 at 15:23

Annotate function give me a wrong result

0 Answers0