按ManyToMany字段长度过滤：values_list()返回，但过滤结果为空

Question

I have such a model in Django :

class VariantTag():                                                                                           
    saved_variants = models.ManyToManyField('SavedVariant')                                                                
    variant_tag_type = models.ForeignKey('VariantTagType', on_delete=models.CASCADE)  

Then, I am trying to get the VariantTag models with saved_variants field of length 2 which contain at least one of the id from the variant_ids pk list:

het_tags = (VariantTag.objects.annotate(variant_len=Count('saved_variants'))) \                                     
            .filter(saved_variants__in=variant_ids, variant_len=2)                                                      
logger.info(het_tags.all())                                                                                         
het_variant_ids = het_tags.values_list('saved_variants', flat=True)                                               
logger.info('******* het_variant_ids: {}'.format(het_variant_ids))

Logger output that I get is the following:

<QuerySet []>
******* het_variant_ids: <QuerySet [150, 149]>

Where 150 and 149 are correct ids that I am looking for. However, I need to get full QuerySet objects, how to get them? Why is it not working?

Update

Both query conditions are working on their own separately, but applied together they give an empty result. According to the data I have in the models that should not happen.

Answer 1

I am not sure why but restructuring of the query to do the filtering first for ids, then annotation, and only then filtering by length of ManyToMany field worked out:

het_tags = (VariantTag.objects.filter(saved_variants__in=variant_ids)
                              .annotate(variant_len=Count('saved_variants')))
                              .filter(variant_len=2)

If you have any idea of why this works, please, post another answer.