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Getting Datastore Key before inserting data

Cloud Datastore (Entities, Properties, and Keys) allows entities to be identified with an automatically generated numeric ID (or enter a custom name).

I'd like to use the automatically generated numeric ID in some business logic before the entity is written to the Datastore.

from google.cloud import datastore

ds = datastore.Client('my-project-id')

# Use automatically generated numeric ID.
key = ds.key('MyEntity')

# https://googlecloudplatform.github.io/google-cloud-python/latest/datastore/keys.html
my_id = key.id()

# Some business logic requiring unique ID for MyEntity
data = my_business_logic(my_id)

entity = datastore.Entity(key=key)
entity.update(data)
ds.put(entity)


However, key.id() is None and so I get a Python TypeError:

key.id()

None

TypeError: 'NoneType' object is not callable


Key is documented, so perhaps I'm using the wrong getter?

1 Answer
1

By default, entities won't have a complete key (with the numeric ID) until they're put() into the datastore.

put()

For a case like yours where you want to know the auto-generated numeric ID before writing the entity to the datastore, you can use the datastore client's allocate_ids method, like so:

allocate_ids

from google.cloud import datastore

ds = datastore.Client('my-project-id')

key = ds.allocate_ids(ds.key('MyEntity'), 1)[0]

my_id = key.id

data = my_business_logic(my_id)

entity = datastore.Entity(key=key)
entity.update(data)
ds.put(entity)


Note that allocate_ids takes 2 arguments, incomplete_key and num_ids, so even if you just want one key, you'll need to specify that and extract the first (and only) member of the resulting list.

allocate_ids

incomplete_key

num_ids

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