DB 遷移至 NDB 用戶端程式庫

無需對 Datastore 進行任何變更

如果您想知道，儘管 API 不同，NDB 和舊版 ext.db 套件會寫入「完全」相同的資料到 Datastore。這代表您不用執行任何轉換到資料儲存庫的作業，而且只要使用相同的結構定義，就能輕鬆混合和比對 NDB 與 ext.db 程式碼。您甚至還可使用 ndb.Key.from_old_key() 和 key.to_old_key() 在 ext.db 和 NDB 索引鍵之間轉換。

一般差異

  • NDB 有嚴格的類型要求。例如在 DB 中，如果需要的是索引鍵，您也可以傳送實體或字串。在 NDB 中，您就必須傳送索引鍵。

  • NDB 有嚴格的清單要求。例如在資料庫中，db.put() 會接收實體或實體清單。在 NDB 中，您可以使用 entity.put() 放置單一實體，但使用 ndb.put_multi(<list>) 放置實體清單。

  • NDB 偏好方法而非函式。例如，NDB 使用 key.get() 和 entity.put()，而非 db.get(key) 和 db.put(entity)。

  • NDB 不喜歡提供兩個 API 來執行相同的工作 (另一方面，NDB 有時會提供兩個 API 來執行有些許不同的工作)。

API 呼叫並行比較

下表列出 ndb 和舊版 ext.db 模組之間的相同與相異之處。請參閱 NDB 官方文件，瞭解 NDB 的簡介說明與參考資料。

模型類別

google.appengine.ext.db ndb.model 
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 () !!

實體

google.appengine.ext.db ndb.model 
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()

沒有直接對應項目；請查看 Stack Overflow 解答以取得可能的解決方案。

取得

google.appengine.ext.db ndb.model 
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')

Put

google.appengine.ext.db ndb.model 
db.put(model_instance)
 
model_instance.put()
 
db.put(list_of_model_instances)
 
ndb.put_multi(
  list_of_model_instances)

刪除

google.appengine.ext.db ndb.model 
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)

屬性

google.appengine.ext.db ndb.model 
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()

沒有對應項目。

 
db.IntegerProperty()
 
ndb.IntegerProperty()
 
db.LinkProperty()
 
ndb.StringProperty()

大小上限為 500。如需更長的網址，請使用 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)

不支援；字串一律可包含 \n。

 
db.StringListProperty()
 
ndb.StringProperty(repeated=True)
 
db.TextProperty()
 
ndb.TextProperty()
 
db.TimeProperty()
 
ndb.TimeProperty()
 
db.UserProperty()
 
ndb.UserProperty()
 
blobstore.BlobReferenceProperty()
 
ndb.BlobKeyProperty()

建構索引鍵

google.appengine.ext.db ndb.model 
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')

金鑰操作

google.appengine.ext.db ndb.model 
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()

相同。

 
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

交易

google.appengine.ext.db ndb.model 
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)

查詢

google.appengine.ext.db ndb.model 
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

游標

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

在 NDB 中，more 是指示游標位置是否有更多實體的 bool。

 
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)