Move ndb entities code snippets into github

Author: Jerjou Cheng

appengine/ndb/entities/README.md

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+## App Engine Datastore NDB Entities Samples
+
+This contains snippets used in the NDB entity documentation, demonstrating
+various operation on ndb entities.
+
+<!-- auto-doc-link -->
+These samples are used on the following documentation page:
+
+> https://cloud.google.com/appengine/docs/python/ndb/entities
+
+<!-- end-auto-doc-link -->

appengine/ndb/entities/snippets.py

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+# Copyright 2016 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from google.appengine.ext import ndb
+
+
+class Account(ndb.Model):
+    username = ndb.StringProperty()
+    userid = ndb.IntegerProperty()
+    email = ndb.StringProperty()
+
+
+def create_model_using_keyword_arguments():
+    sandy = Account(
+        username='Sandy', userid=123, email='[email protected]')
+    return sandy
+
+
+def create_model_using_attributes():
+    sandy = Account()
+    sandy.username = 'Sandy'
+    sandy.userid = 123
+    sandy.email = '[email protected]'
+    return sandy
+
+
+def demonstrate_model_constructor_type_checking():
+    bad = Account(
+        username='Sandy', userid='not integer')  # raises an exception
+    return bad
+
+
+def dmonstrate_model_attribute_type_checking(sandy):
+    sandy.username = 42  # raises an exception
+
+
+def save_model(sandy):
+    sandy_key = sandy.put()
+    return sandy_key
+
+
+def get_url_safe_key(sandy_key):
+    url_string = sandy_key.urlsafe()
+    return url_string
+
+
+def get_model_from_url_safe_key(url_string):
+    sandy_key = ndb.Key(urlsafe=url_string)
+    sandy = sandy_key.get()
+    return sandy
+
+
+def get_key_and_numeric_id_from_url_safe_key(url_string):
+    key = ndb.Key(urlsafe=url_string)
+    kind_string = key.kind()
+    ident = key.id()
+    return key, ident, kind_string
+
+
+def update_model_from_key(key):
+    sandy = key.get()
+    sandy.email = '[email protected]'
+    sandy.put()
+
+
+def delete_model(sandy):
+    sandy.key.delete()
+
+
+def create_model_with_named_key():
+    account = Account(
+        username='Sandy', userid=1234, email='[email protected]',
+        id='[email protected]')
+
+    return account.key.id()  # returns '[email protected]'
+
+
+def set_key_directly(account):
+    account.key = ndb.Key('Account', '[email protected]')
+
+    # You can also use the model class object itself, rather than its name,
+    # to specify the entity's kind:
+    account.key = ndb.Key(Account, '[email protected]')
+
+
+def create_model_with_generated_id():
+    # note: no id kwarg
+    account = Account(username='Sandy', userid=1234, email='[email protected]')
+    account.put()
+    # Account.key will now have a key of the form: ndb.Key(Account, 71321839)
+    # where the value 71321839 was generated by Datastore for us.
+    return account
+
+
+class Revision(ndb.Model):
+    message_text = ndb.StringProperty()
+
+
+def demonstrate_models_with_parent_hierarchy():
+    ndb.Key('Account', '[email protected]', 'Message', 123, 'Revision', '1')
+    ndb.Key('Account', '[email protected]', 'Message', 123, 'Revision', '2')
+    ndb.Key('Account', '[email protected]', 'Message', 456, 'Revision', '1')
+    ndb.Key('Account', '[email protected]', 'Message', 789, 'Revision', '2')
+
+
+def equivalent_ways_to_define_key_with_parent():
+    ndb.Key('Account', '[email protected]', 'Message', 123, 'Revision', '1')
+
+    ndb.Key('Revision', '1', parent=ndb.Key(
+        'Account', '[email protected]', 'Message', 123))
+
+    ndb.Key('Revision', '1', parent=ndb.Key(
+        'Message', 123, parent=ndb.Key('Account', '[email protected]')))
+
+    sandy_key = ndb.Key(Account, '[email protected]')
+    return sandy_key
+
+
+def create_model_with_parent_keys():
+    account_key = ndb.Key(Account, '[email protected]')
+
+    # Ask Datastore to allocate an ID.
+    new_id = ndb.Model.allocate_ids(size=1, parent=account_key)[0]
+
+    # Datastore returns us an integer ID that we can use to create the message
+    # key
+    message_key = ndb.Key('Message', new_id, parent=account_key)
+
+    # Now we can put the message into Datastore
+    initial_revision = Revision(
+        message_text='Hello', id='1', parent=message_key)
+    initial_revision.put()
+
+    return initial_revision
+
+
+def get_parent_key_of_model(initial_revision):
+    message_key = initial_revision.key.parent()
+    return message_key
+
+
+def operate_on_multiple_keys_at_once(list_of_entities):
+    list_of_keys = ndb.put_multi(list_of_entities)
+    list_of_entities = ndb.get_multi(list_of_keys)
+    ndb.delete_multi(list_of_keys)
+
+
+class Mine(ndb.Expando):
+    pass
+
+
+def create_expando_model():
+    e = Mine()
+    e.foo = 1
+    e.bar = 'blah'
+    e.tags = ['exp', 'and', 'oh']
+    e.put()
+
+    return e
+
+
+def get_properties_defined_on_expando(e):
+    return e._properties
+    # {
+    #     'foo': GenericProperty('foo'),
+    #     'bar': GenericProperty('bar'),
+    #     'tags': GenericProperty('tags', repeated=True)
+    # }
+
+
+class FlexEmployee(ndb.Expando):
+    name = ndb.StringProperty()
+    age = ndb.IntegerProperty()
+
+
+def create_expando_model_with_defined_properties():
+    employee = FlexEmployee(name='Sandy', location='SF')
+    return employee
+
+
+class Specialized(ndb.Expando):
+    _default_indexed = False
+
+
+def create_expando_model_that_isnt_indexed_by_default():
+    e = Specialized(foo='a', bar=['b'])
+    return e._properties
+    # {
+    #     'foo': GenericProperty('foo', indexed=False),
+    #     'bar': GenericProperty('bar', indexed=False, repeated=True)
+    # }
+
+
+def demonstrate_wrong_way_to_query_expando():
+    FlexEmployee.query(FlexEmployee.location == 'SF')
+
+
+def demonstrate_right_way_to_query_expando():
+    FlexEmployee.query(ndb.GenericProperty('location') == 'SF')
+
+
+notification = None
+
+
+def _notify(message):
+    global notification
+    notification = message
+
+
+class Friend(ndb.Model):
+    name = ndb.StringProperty()
+
+    def _pre_put_hook(self):
+        _notify('Gee wiz I have a new friend!')
+
+    @classmethod
+    def _post_delete_hook(cls, key, future):
+        _notify('I have found occasion to rethink our friendship.')
+
+
+def demonstrate_model_put_and_delete_hooks():
+    f = Friend()
+    f.name = 'Carole King'
+    f.put()  # _pre_put_hook is called
+    yield f
+    fut = f.key.delete_async()  # _post_delete_hook not yet called
+    fut.get_result()  # _post_delete_hook is called
+    yield f
+
+
+class MyModel(ndb.Model):
+    pass
+
+
+def reserve_model_ids():
+    first, last = MyModel.allocate_ids(100)
+    return first, last
+
+
+def reserve_model_ids_with_a_parent(p):
+    first, last = MyModel.allocate_ids(100, parent=p)
+    return first, last
+
+
+def construct_keys_from_range_of_reserved_ids(first, last):
+    keys = [ndb.Key(MyModel, id) for id in range(first, last+1)]
+    return keys
+
+
+def reserve_model_ids_up_to(N):
+    first, last = MyModel.allocate_ids(max=N)
+    return first, last