Fetching just the Key/id from a ReferenceProperty in App Engine
- by ozone
Hi SO, I could use a little help in AppEngine land...
Using the [Python] API I create relationships like this example from the docs:
class Author(db.Model):
name = db.StringProperty()
class Story(db.Model):
author = db.ReferenceProperty(Author)
story = db.get(story_key)
author_name = story.author.name
As I understand it, that example will make two datastore queries. One to fetch the Story and then one to deference the Author inorder to access the name. But I want to be able to fetch the id, so do something like:
story = db.get(story_key)
author_id = story.author.key().id()
I want to just get the id from the reference. I do not want to have to deference (therefore query the datastore) the ReferenceProperty value.
From reading the documentation it says that
the value of a ReferenceProperty is a Key
Which leads me to think that I could just call .id() on the reference's value. But it also says:
The ReferenceProperty model provides features for Key property values such as automatic dereferencing.
I can't find anything that explains when this referencing takes place?
Is it safe to call .id() on the ReferenceProperty's value?
Can it be assumed that calling .id() will not cause a datastore lookup?
