data modeling - Google Datastore deletes and multiple parents -

i have data model in entity a contains references 2 other entities, b , c. if either b or c deleted, want a deleted.

when creating a, it's possible name either b or c parent. possible name both b , c parents if either b or c deleted, a deleted?

in more concrete terms, search results, result might have both category , region, web page birds in north america. result stored reference category , region. later, want delete category birds , want result deleted. likewise, delete region north america , want result deleted.

i hate go on @ such length such trivial scenario. doesn't seem covered in of datastore documentation. missing? flawed data model?

single-parent limitation:

a child can have 1 parent in datastore. in other words, a can child of b or c, not both. of course, parent can have multiple children, though.

alternative:

you can use keyproperty repeated=true argument , store many entity keys on it. in python, this:

class a(ndb.model):     associated_with = ndb.keyproperty(repeated=true)     some_other_property = ndb.stringproperty()  a_entity = a(     associated_with = [b_key, c_key],     some_other_property = 'any value' ) a_entity.put() 

automatically triggering deletes:

datastore doesn't offer functionality out of box, can mimic in application. 1 idea implementing in python, example, extend model class own delete method (haven't tested code, it's illustration):

class a(ndb.model):     associated_with = ndb.keyproperty(repeated=true)     some_other_property = ndb.stringproperty()      def delete_ext(entity):  # entity object         if entity.associated_with:             associated in entity.associated_with:                 associated.delete()         entity.key.delete() 

you may want wrap deletes in transaction. beware single transaction can operate on 25 entity groups.