many to many - Django QuerySet join across four tables, including ManyToMany? -

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given following models, goal create queryset pulls available tag objects given postcategory id. know how write in sql can't figure out how using django orm. believe i'm following best practices defining relationships on post object, , not tag, queryset syntax pattern seems expect me start tag.objects.filter() don't see how.

class tag(models.model):     name = models.charfield(max_length=255)  class postcategory(models.model):     name = models.charfield(max_length=100)      class post(models.model):     body_text = models.textfield()     pub_date = models.datetimefield()     mod_date = models.datetimefield(auto_now=true)     title = models.charfield(max_length=255)     subtitle = models.charfield(max_length=255)      is_featured = models.booleanfield()     image = models.imagefield(upload_to='post_images')     tags = models.manytomanyfield(tag, null=true, blank=true)     user = models.foreignkey(user)     category = models.foreignkey(postcategory) 

tags = tag.objects.filter(post__category_id=postcategory_id).distinct()

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