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Showing content from http://cloud.google.com/appengine/docs/legacy/standard/python/ndb/db_to_ndb below:

DB to NDB Client Library Migration | App Engine standard environment for Python 2

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In case you wondered, despite the different APIs, NDB and the old ext.db package write exactly the same data to the Datastore. That means you don’t have to do any conversion to your datastore, and you can happily mix and match NDB and ext.db code, as long as the schema you use is equivalent. You can even convert between ext.db and NDB keys using ndb.Key.from_old_key() and key.to_old_key().

• NDB is picky about types. E.g. in db, when a key is required, you can also pass an entity or a string. In NDB you must pass a key.

• NDB is picky about lists. E.g. in db, db.put() takes either an entity or a list of entities. In NDB, you use entity.put() to put a single entity, but ndb.put_multi(<list>) to put a list of entities.

• NDB prefers methods over functions. E.g. instead of db.get(key), and db.put(entity), NDB uses key.get() and entity.put().

• NDB doesn't like offering two APIs that do the same thing. (On the other hand it does sometimes offer two APIs that do slightly different things.)

The tables below show similarities and differences between ndb and the old ext.db module. See the Official NDB Docs for an introduction to and reference for NDB.

class MyModel(db.Model):
  foo = db.StringProperty()

class MyModel(ndb.Model):
  foo = ndb.StringProperty()

@classmethod
def kind(cls):
  return 'Foo'

@classmethod
def _get_kind(cls):
  return 'Foo'

MyModel.kind()

MyModel._get_kind()

MyModel.properties()
model_instance.properties()

MyModel._properties  # No () !!
model_entity._properties

MyExpando.dynamic_properties()

MyExpando._properties  # No () !!

MyModel(key_name='my_key')

MyModel(id='my_key')

MyModel(key_name='my_key',
  parent=model_instance)

MyModel(id='my_key',
  parent=model_instance.key)

key = model_instance.key()

key = model_instance.key  # No () !!

model_instance = MyModel(
  foo='foo',
  bar='bar',
  baz='baz')

model_instance = MyModel(
  foo='foo',
  bar='bar',
  baz='baz')

model_instance.foo = 'foo'
model_instance.bar = 'bar'
model_instance.baz = 'baz'

model_instance.foo = 'foo'
model_instance.bar = 'bar'
model_instance.baz = 'baz'
# or a shortcut...
model_instance.populate(
  foo='foo',
  bar='bar',
  baz='baz')

model_instance.is_saved()

No direct equivalent; see Stack Overflow for a possible solution.

MyModel.get_by_key_name('my_key')

MyModel.get_by_id('my_key')

MyModel.get_by_id(42)

MyModel.get_by_id(42)

db.get(key)

key.get()

MyModel.get(key)

key.get()

db.get(model_instance)

model_instance.key.get()

db.get(list_of_keys)

ndb.get_multi(list_of_keys)

db.get(list_of_instances)

ndb.get_multi([x.key for x in
               list_of_instances])

MyModel.get_or_insert('my_key',
  parent=model_instance,
  foo='bar')

MyModel.get_or_insert('my_key',
  parent=model_instance.key,
  foo='bar')

db.put(model_instance)

model_instance.put()

db.put(list_of_model_instances)

ndb.put_multi(
  list_of_model_instances)

model_instance.delete()

model_instance.key.delete()

db.delete(model_instance)

model_instance.key.delete()

db.delete(key)

key.delete()

db.delete(list_of_model_instances)

ndb.delete_multi([m.key for m in
  list_of_model_instances])

db.delete(list_of_keys)

ndb.delete_multi(list_of_keys)

db.BlobProperty()

ndb.BlobProperty()

db.BooleanProperty()

ndb.BooleanProperty()

db.ByteStringProperty()

ndb.BlobProperty(indexed=True)

db.CategoryProperty()

ndb.StringProperty()

db.DateProperty()

ndb.DateProperty()

db.DateTimeProperty()

ndb.DateTimeProperty()

db.EmailProperty()

ndb.StringProperty()

db.FloatProperty()

ndb.FloatProperty()

db.GeoPtProperty()

ndb.GeoPtProperty()

db.IMProperty()

No equivalent.

db.IntegerProperty()

ndb.IntegerProperty()

db.LinkProperty()

ndb.StringProperty()

Has a max size of 500. For longer URLs, use ndb.TextProperty().

db.ListProperty(bool)
db.ListProperty(float)
db.ListProperty(int)
db.ListProperty(db.Key)
# etc.

ndb.BooleanProperty(repeated=True)
ndb.FloatProperty(repeated=True)
ndb.IntegerProperty(repeated=True)
ndb.KeyProperty(repeated=True)
# etc.

db.PhoneNumberProperty()

ndb.StringProperty()

db.PostalAddressProperty()

ndb.StringProperty()

db.RatingProperty()

ndb.IntegerProperty()

db.ReferenceProperty(AnotherModel)
model_instance.prop
MyModel.prop \
  .get_value_for_datastore \
  (model_instance)

ndb.KeyProperty(kind=AnotherModel)
model_instance.prop.get()
model_instance.prop

# Using the backreference set
other = model_instance.prop
other.prop_set.fetch(N)

# No direct equivalent; emulation:
other = model_instance.prop.get()
MyModel.query(
  MyModel.prop == other.key).fetch(N)

db.SelfReferenceProperty()

ndb.KeyProperty(kind='ThisModelClass')

db.StringProperty()

ndb.StringProperty()

db.StringProperty(multiline=True)

Not supported; strings are always allowed to contain \n.

db.StringListProperty()

ndb.StringProperty(repeated=True)

db.TextProperty()

ndb.TextProperty()

db.TimeProperty()

ndb.TimeProperty()

db.UserProperty()

ndb.UserProperty()

blobstore.BlobReferenceProperty()

ndb.BlobKeyProperty()

key = db.Key(encoded_key)

key = ndb.Key(urlsafe=encoded_key)

key = db.Key.from_path(
  'MyKind', 'some_id',
  'MyKind', 'some_id')

key = ndb.Key(
  'MyKind', 'some_id',
  'MyKind', 'some_id')

key = db.Key.from_path(
  MyModel, 'some_id',
  parent=model_instance,
  namespace='my_namespace')

key = ndb.Key(
  MyModel, 'some_id',
  parent=model_instance.key,
  namespace='my_namespace')

key.id_or_name()

key.id()

key.id()

key.integer_id()

key.name()

key.string_id()

key.has_id_or_name()

key.id() is None
# or...
model_instance.has_complete_key()

key.app(), key.namespace(),
key.parent(), key.kind()

Same.

str(key)

key.urlsafe()

key.to_path()

key.flat()

db.allocate_ids(MyModel, size)

S, E = MyModel.allocate_ids(size)

db.allocate_id_range(MyModel,X,Y)

S, E = MyModel.allocate_ids(max=Y)
assert S <= X

db.run_in_transaction(function)

ndb.transaction(function)

db.run_in_transaction(
  function, *args, **kwds)

ndb.transaction(
  lambda: function(*args, **kwds))

db.run_in_transaction_custom_retries(n, function)

ndb.transaction(function, retries=n)

opts = \
  db.create_transaction_options(xg=True)
db.run_in_transaction_options(opts, fun)

ndb.transaction(fun, xg=True)

q = MyModel.all()

q = MyModel.query()

for result in q.run(): ...

for result in q.iter(): ...

q = MyModel.all() \
  .filter('foo =', 'bar') \
  .filter('baz >=', 'ding')

q = MyModel.query(
  MyModel.foo == 'bar',
  MyModel.baz >= 'ding')

q = MyModel.all()
q.filter('foo =', 'bar')
q.filter('baz >=', 'ding')
q.order('-foo')
results = q.fetch(10)

q = MyModel.query()
q = q.filter(MyModel.foo == 'bar')
q = q.filter(MyModel.baz >= 'ding')
q = q.order(-MyModel.foo)
results = q.fetch(10)

q.filter('__key__', k)
# k is a db.Key instance

q = q.filter(MyModel._key == k)
# k is an ndb.Key instance

a.filter('__key__ >=', k)
# k is a db.Key instance

q = q.filter(MyModel._key >= k)
# k is an ndb.Key instance

class MyExpando(Expando): pass
q = MyExpando.all()
q.filter('foo =', 'bar')

class MyExpando(Expando): pass
q = MyExpando.query(
 ndb.GenericProperty('foo') == 'bar')

class Foo(Model): ...
class Bar(Model):
  foo = ReferenceProperty(Foo)
myfoo = <some Foo instance>
for bar in myfoo.bar_set(): ...

class Foo(Model): ...
class Bar(Model):
  foo = KeyProperty(kind=Foo)
myfoo = <some Foo instance>
for bar in \
  Bar.query(Bar.foo == myfoo.key): ...

q = MyModel.all()
q.ancestor(ancestor_key)

q =
  MyModel.query(ancestor=ancestor_key)

q = MyModel.all(keys_only=True)
r = q.fetch(N)

r = MyModel.query() \
    .fetch(N, keys_only=True)
# Alternatively:
q = MyModel.query(
      default_options=QueryOptions(
                      keys_only=True))
r = q.fetch(N)

q = MyModel.gql(...)

# same thing

q = MyModel.all()
a = q.fetch(20)
cur = q.cursor()

q = MyModel.query()
a, cur, more = q.fetch_page(20)

In NDB, more is a bool indicating whether there are more entities at the cursor.

q.with_cursor(cur)
b = q.fetch(20)

b, cur, more = \
  q.fetch_page(20, start_cursor=cur)

q.with_cursor(end_cursor=cur)
b = q.fetch(20)

q.fetch(20, end_cursor=cur)

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2025-06-16 UTC.

[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-06-16 UTC."],[[["NDB and ext.db write the same data to the Datastore, allowing you to mix and match code from both APIs without needing to convert your existing datastore."],["NDB is stricter about types, requiring you to pass keys directly instead of entities or strings, and using dedicated methods like `entity.put()` or `ndb.put_multi(\u003clist\u003e)` instead of `db.put()`."],["NDB utilizes methods over functions for common operations, such as `key.get()` instead of `db.get(key)`."],["The side-by-side comparison tables show the similarities and the differences between `ndb` and the older `ext.db` module."],["`NDB` offers a similar API to the old `ext.db` module for Model class, Entities, Get, Put, Delete, Properties, Building a key, Key operations, Transactions, Queries and Cursors, allowing for easy migration."]]],[]]

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