Finding intersection of two querysets of two different models

Question

My models.py looks something like

class RelevanceRelation(TimeStampable, SoftDeletable, models.Model):
    relevance_type = models.ForeignKey(
        RelevanceType,
        on_delete=models.CASCADE,
        related_name="relevance_relations"
    )
    name = models.CharField(max_length=256,
                            verbose_name="Relevance Relation Name")

    def __str__(self):
        return self.name


class RelevanceRelationValue(TimeStampable, SoftDeletable, models.Model):
    entity = models.ForeignKey(
        Entity, on_delete=models.CASCADE,
        related_name="relevance_relation_values"
    )
    relevance_relation = models.ForeignKey(
        RelevanceRelation,
        on_delete=models.CASCADE,
        related_name="values"
    )
    name = models.CharField(max_length=256,
                             verbose_name="Relevance Relation Value")

    def __str__(self):
        return self.name

And I have two querysets

q1 = RelevanceRelationValue.objects.filter(entity=<int>)
q2 = RelevanceRelation.objects.filter(relevance_type=<int>)

Now is there a way to find intersection of q1 and q2 i.e I wan't to display all the values of q2 whose id is present in q1 as rulevance_relation

For example:

q1 = -------------------------------
     | entity | relevance_relation |
     -------------------------------
     |   1    |        1           |
     |   1    |        2           |
     |   1    |        3           |
     -------------------------------

and q2 = -------------------------------
         |   id.  | relevance_type     |
         -------------------------------
         |   1    |        1           |
         |   2    |        1           |
         |   3    |        1           |
         |   4    |        1           |
         |   5    |        1           |
         |   6    |        1           |
         ------------------------------- 

so q3 should be 
         -------------------------------
         |   id.  | relevance_type     |
         -------------------------------
         |   1    |        1           |
         |   2    |        1           |
         |   3    |        1           |
         -------------------------------

willeM_ Van Onsem · Accepted Answer · 2020-05-23 11:21:37Z

1

You can perform extra filtering:

q1 = RelevanceRelationValue.objects.filter(entity=some_value₁).values('relevance_relation')
q2 = RelevanceRelation.objects.filter(
    relevance_type=some_value₂,
    id__in=q1
)

But it makes more sense to simply filter on the related model, so:

RelevanceRelation.objects.filter(
    values__entity=some_value₁,
    relevance_type=some_value₂
).distinct()

Here we thus get all RelevanceRelations for which the relevance_type is some_value₂, and for which a related RelevanceRelationValue exists with entity=some_value₁.

edited May 23, 2020 at 11:21

answered May 23, 2020 at 11:11

willeM_ Van Onsem

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3 Comments

Jack Over a year ago

I am getting an error Original exception text was: 'RelevanceRelation' object has no attribute 'entity_type'.

willeM_ Van Onsem Over a year ago

@Jack: well that is correct, a RelevanceRelation has indeed no attriubte .entity_type, so likely further in you code you aim to obtain attributes that do not exist for the given model.

Jack Over a year ago

oh yes I was calling wrong serialiser and Thank You for the help

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