Key

Provides a Key for Google Cloud Datastore.

A key encapsulates the following pieces of information, which together uniquely designate a (possible) entity in Google Cloud Datastore:

  • a Google Cloud Platform project (a string)

  • a list of one or more (kind, id) pairs where kind is a string and id is either a string or an integer

  • an optional namespace (a string)

The application ID must always be part of the key, but since most applications can only access their own entities, it defaults to the current application ID and you rarely need to worry about it.

The namespace designates a top-level partition of the key space for a particular application. If you’ve never heard of namespaces, you can safely ignore this feature.

Most of the action is in the (kind, id) pairs. A key must have at least one (kind, id) pair. The last (kind, id) pair gives the kind and the ID of the entity that the key refers to, the others merely specify a “parent key”.

The kind is a string giving the name of the model class used to represent the entity. In more traditional databases this would be the table name. A model class is a Python class derived from Model. Only the class name itself is used as the kind. This means all your model classes must be uniquely named within one application. You can override this on a per-class basis.

The ID is either a string or an integer. When the ID is a string, the application is in control of how it assigns IDs. For example, you could use an email address as the ID for Account entities.

To use integer IDs, it’s common to let the datastore choose a unique ID for an entity when first inserted into the datastore. The ID can be set to None to represent the key for an entity that hasn’t yet been inserted into the datastore. The completed key (including the assigned ID) will be returned after the entity is successfully inserted into the datastore.

A key for which the ID of the last (kind, id) pair is set to None is called an incomplete key or partial key. Such keys can only be used to insert entities into the datastore.

A key with exactly one (kind, id) pair is called a top level key or a root key. Top level keys are also used as entity groups, which play a role in transaction management.

If there is more than one (kind, id) pair, all but the last pair represent the “ancestor path”, also known as the key of the “parent entity”.

Other constraints:

  • Kinds and string IDs must not be empty and must be at most 1500 bytes long (after UTF-8 encoding)

  • Integer IDs must be at least 1 and at most 2**63 - 1 (i.e. the positive part of the range for a 64-bit signed integer)

In the “legacy” Google App Engine runtime, the default namespace could be set via the namespace manager (google.appengine.api.namespace_manager). On the gVisor Google App Engine runtime (e.g. Python 3.7), the namespace manager is not available so the default is to have an unset or empty namespace. To explicitly select the empty namespace pass namespace="".

class google.cloud.ndb.key.Key(*path_args, **kwargs)[source]

Bases: object

An immutable datastore key.

For flexibility and convenience, multiple constructor signatures are supported.

The primary way to construct a key is using positional arguments:

>>> ndb.Key(kind1, id1, kind2, id2)
Key('Parent', 'C', 'Child', 42)

This is shorthand for either of the following two longer forms:

>>> ndb.Key(pairs=[(kind1, id1), (kind2, id2)])
Key('Parent', 'C', 'Child', 42)
>>> ndb.Key(flat=[kind1, id1, kind2, id2])
Key('Parent', 'C', 'Child', 42)

Either of the above constructor forms can additionally pass in another key via the parent keyword. The (kind, id) pairs of the parent key are inserted before the (kind, id) pairs passed explicitly.

>>> parent = ndb.Key(kind1, id1)
>>> parent
Key('Parent', 'C')
>>> ndb.Key(kind2, id2, parent=parent)
Key('Parent', 'C', 'Child', 42)

You can also construct a Key from a “urlsafe” encoded string:

>>> ndb.Key(urlsafe=b"agdleGFtcGxlcgsLEgRLaW5kGLkKDA")
Key('Kind', 1337, project='example')

For rare use cases the following constructors exist:

>>> # Passing in a low-level Reference object
>>> reference
app: "example"
path {
  Element {
    type: "Kind"
    id: 1337
  }
}

>>> ndb.Key(reference=reference)
Key('Kind', 1337, project='example')
>>> # Passing in a serialized low-level Reference
>>> serialized = reference.SerializeToString()
>>> serialized
b'j\x07exampler\x0b\x0b\x12\x04Kind\x18\xb9\n\x0c'
>>> ndb.Key(serialized=serialized)
Key('Kind', 1337, project='example')
>>> # For unpickling, the same as ndb.Key(**kwargs)
>>> kwargs = {"pairs": [("Cheese", "Cheddar")], "namespace": "good"}
>>> ndb.Key(kwargs)
Key('Cheese', 'Cheddar', namespace='good')

The “urlsafe” string is really a websafe-base64-encoded serialized Reference, but it’s best to think of it as just an opaque unique string.

If a Reference is passed (using one of the reference, serialized or urlsafe keywords), the positional arguments and namespace must match what is already present in the Reference (after decoding if necessary). The parent keyword cannot be combined with a Reference in any form.

Keys are immutable, which means that a Key object cannot be modified once it has been created. This is enforced by the implementation as well as Python allows.

Keys also support interaction with the datastore; the methods get(), get_async(), delete() and delete_async() are the only ones that engage in any kind of I/O activity.

Keys may be pickled.

Subclassing Key is best avoided; it would be hard to get right.

Parameters
  • path_args (Union[Tuple[str, ..], Tuple[Dict]]) – Either a tuple of (kind, id) pairs or a single dictionary containing only keyword arguments.

  • reference (Optional[ Reference]) – A reference protobuf representing a key.

  • serialized (Optional[bytes]) – A reference protobuf serialized to bytes.

  • urlsafe (Optional[str]) – A reference protobuf serialized to bytes. The raw bytes are then converted to a websafe base64-encoded string.

  • pairs (Optional[Iterable[Tuple[str, Union[str, int]]]]) – An iterable of (kind, id) pairs. If this argument is used, then path_args should be empty.

  • flat (Optional[Iterable[Union[str, int]]]) – An iterable of the (kind, id) pairs but flattened into a single value. For example, the pairs [("Parent", 1), ("Child", "a")] would be flattened to ["Parent", 1, "Child", "a"].

  • project (Optional[str]) – The Google Cloud Platform project (previously on Google App Engine, this was called the Application ID).

  • app (Optional[str]) – DEPRECATED: Synonym for project.

  • namespace (Optional[str]) – The namespace for the key.

  • parent (Optional[Key]) – The parent of the key being constructed. If provided, the key path will be relative to the parent key’s path.

Raises

TypeError – If none of reference, serialized, urlsafe, pairs or flat is provided as an argument and no positional arguments were given with the path.

__eq__(other)[source]

Equality comparison operation.

__ge__(other)[source]

Greater than or equal ordering.

__getnewargs__()[source]

Private API used to specify __new__ arguments when unpickling.

Note

This method is provided for backwards compatibility, though it isn’t needed.

Returns

A tuple containing a single dictionary of state to pickle. The dictionary has three keys pairs, app and namespace.

Return type

Tuple[Dict[str, Any]]

__getstate__()[source]

Private API used for pickling.

Returns

A tuple containing a single dictionary of state to pickle. The dictionary has three keys pairs, app and namespace.

Return type

Tuple[Dict[str, Any]]

__gt__(other)[source]

Greater than ordering.

__hash__()[source]

Hash value, for use in dictionary lookups.

Note

This ignores app and namespace. Since hash() isn’t expected to return a unique value (it just reduces the chance of collision), this doesn’t try to increase entropy by including other values. The primary concern is that hashes of equal keys are equal, not the other way around.

__le__(other)[source]

Less than or equal ordering.

__lt__(other)[source]

Less than ordering.

__ne__(other)[source]

The opposite of __eq__.

__repr__()[source]

String representation used by str() and repr().

We produce a short string that conveys all relevant information, suppressing project and namespace when they are equal to the default. In many cases, this string should be able to be used to invoke the constructor.

For example:

>>> key = ndb.Key("hi", 100)
>>> repr(key)
"Key('hi', 100)"
>>>
>>> key = ndb.Key(
...     "bye", "hundred", project="specific", namespace="space"
... )
>>> str(key)
"Key('bye', 'hundred', project='specific', namespace='space')"
__setstate__(state)[source]

Private API used for unpickling.

Parameters

state (Tuple[Dict[str, Any]]) – A tuple containing a single dictionary of pickled state. This should match the signature returned from __getstate__(), in particular, it should have three keys pairs, app and namespace.

Raises
  • TypeError – If the state does not have length 1.

  • TypeError – If the single element in state is not a dictionary.

__str__()[source]

Alias for __repr__().

app()

The project ID for the key.

Warning

This may differ from the original app passed in to the constructor. This is because prefixed application IDs like s~example are “legacy” identifiers from Google App Engine. They have been replaced by equivalent project IDs, e.g. here it would be example.

>>> key = ndb.Key("A", "B", project="s~example")
>>> key.project()
'example'
>>>
>>> key = ndb.Key("A", "B", project="example")
>>> key.project()
'example'
delete(**kwargs)[source]

Synchronously delete the entity for this key.

This is a no-op if no such entity exists.

Note

If in a transaction, the entity can only be deleted at transaction commit time. In that case, this function will schedule the entity to be deleted as part of the transaction and will return immediately, which is effectively the same as calling delete_async() and ignoring the returned future. If not in a transaction, this function will block synchronously until the entity is deleted, as one would expect.

Parameters
  • timeout (float) – Override the gRPC timeout, in seconds.

  • deadline (float) – DEPRECATED: Synonym for timeout.

  • use_cache (bool) – Specifies whether to store entities in in-process cache; overrides in-process cache policy for this operation.

  • use_global_cache (bool) – Specifies whether to store entities in global cache; overrides global cache policy for this operation.

  • use_datastore (bool) – Specifies whether to store entities in Datastore; overrides Datastore policy for this operation.

  • global_cache_timeout (int) – Maximum lifetime for entities in global cache; overrides global cache timeout policy for this operation.

  • use_memcache (bool) – DEPRECATED: Synonym for use_global_cache.

  • memcache_timeout (int) – DEPRECATED: Synonym for global_cache_timeout.

  • max_memcache_items (int) – No longer supported.

  • force_writes (bool) – No longer supported.

delete_async(**kwargs)[source]

Schedule deletion of the entity for this key.

The result of the returned future becomes available once the deletion is complete. In all cases the future’s result is None (i.e. there is no way to tell whether the entity existed or not).

Parameters
  • timeout (float) – Override the gRPC timeout, in seconds.

  • deadline (float) – DEPRECATED: Synonym for timeout.

  • use_cache (bool) – Specifies whether to store entities in in-process cache; overrides in-process cache policy for this operation.

  • use_global_cache (bool) – Specifies whether to store entities in global cache; overrides global cache policy for this operation.

  • use_datastore (bool) – Specifies whether to store entities in Datastore; overrides Datastore policy for this operation.

  • global_cache_timeout (int) – Maximum lifetime for entities in global cache; overrides global cache timeout policy for this operation.

  • use_memcache (bool) – DEPRECATED: Synonym for use_global_cache.

  • memcache_timeout (int) – DEPRECATED: Synonym for global_cache_timeout.

  • max_memcache_items (int) – No longer supported.

  • force_writes (bool) – No longer supported.

flat()[source]

The flat path for the key.

>>> key = ndb.Key("Satellite", "Moon", "Space", "Dust")
>>> key.flat()
('Satellite', 'Moon', 'Space', 'Dust')
>>>
>>> partial_key = ndb.Key("Known", None)
>>> partial_key.flat()
('Known', None)
classmethod from_old_key(old_key)[source]

Factory constructor to convert from an “old”-style datastore key.

The old_key was expected to be a google.appengine.ext.db.Key (which was an alias for google.appengine.api.datastore_types.Key).

However, the google.appengine.ext.db module was part of the legacy Google App Engine runtime and is not generally available.

Raises

NotImplementedError – Always.

get(**kwargs)[source]

Synchronously get the entity for this key.

Returns the retrieved Model or None if there is no such entity.

Parameters
  • read_consistency – Set this to ndb.EVENTUAL if, instead of waiting for the Datastore to finish applying changes to all returned results, you wish to get possibly-not-current results faster. You can’t do this if using a transaction.

  • transaction (bytes) – Any results returned will be consistent with the Datastore state represented by this transaction id. Defaults to the currently running transaction. Cannot be used with read_consistency=ndb.EVENTUAL.

  • retries (int) – Number of times to retry this operation in the case of transient server errors. Operation will potentially be tried up to retries + 1 times. Set to 0 to try operation only once, with no retries.

  • timeout (float) – Override the gRPC timeout, in seconds.

  • deadline (float) – DEPRECATED: Synonym for timeout.

  • use_cache (bool) – Specifies whether to store entities in in-process cache; overrides in-process cache policy for this operation.

  • use_global_cache (bool) – Specifies whether to store entities in global cache; overrides global cache policy for this operation.

  • use_datastore (bool) – Specifies whether to store entities in Datastore; overrides Datastore policy for this operation.

  • global_cache_timeout (int) – Maximum lifetime for entities in global cache; overrides global cache timeout policy for this operation.

  • use_memcache (bool) – DEPRECATED: Synonym for use_global_cache.

  • memcache_timeout (int) – DEPRECATED: Synonym for global_cache_timeout.

  • max_memcache_items (int) – No longer supported.

  • read_policy – DEPRECATED: Synonym for read_consistency.

  • force_writes (bool) – No longer supported.

Returns

Union[Model, None]

get_async(**kwargs)[source]

Asynchronously get the entity for this key.

The result for the returned future will either be the retrieved Model or None if there is no such entity.

Parameters
  • read_consistency – Set this to ndb.EVENTUAL if, instead of waiting for the Datastore to finish applying changes to all returned results, you wish to get possibly-not-current results faster. You can’t do this if using a transaction.

  • transaction (bytes) – Any results returned will be consistent with the Datastore state represented by this transaction id. Defaults to the currently running transaction. Cannot be used with read_consistency=ndb.EVENTUAL.

  • retries (int) – Number of times to retry this operation in the case of transient server errors. Operation will potentially be tried up to retries + 1 times. Set to 0 to try operation only once, with no retries.

  • timeout (float) – Override the gRPC timeout, in seconds.

  • deadline (float) – DEPRECATED: Synonym for timeout.

  • use_cache (bool) – Specifies whether to store entities in in-process cache; overrides in-process cache policy for this operation.

  • use_global_cache (bool) – Specifies whether to store entities in global cache; overrides global cache policy for this operation.

  • use_datastore (bool) – Specifies whether to store entities in Datastore; overrides Datastore policy for this operation.

  • global_cache_timeout (int) – Maximum lifetime for entities in global cache; overrides global cache timeout policy for this operation.

  • use_memcache (bool) – DEPRECATED: Synonym for use_global_cache.

  • memcache_timeout (int) – DEPRECATED: Synonym for global_cache_timeout.

  • max_memcache_items (int) – No longer supported.

  • read_policy – DEPRECATED: Synonym for read_consistency.

  • force_writes (bool) – No longer supported.

Returns

Future

id()[source]

The string or integer ID in the last (kind, id) pair, if any.

>>> key_int = ndb.Key("A", 37)
>>> key_int.id()
37
>>> key_str = ndb.Key("A", "B")
>>> key_str.id()
'B'
>>> key_partial = ndb.Key("A", None)
>>> key_partial.id() is None
True
integer_id()[source]

The string ID in the last (kind, id) pair, if any.

>>> key_int = ndb.Key("A", 37)
>>> key_int.integer_id()
37
>>> key_str = ndb.Key("A", "B")
>>> key_str.integer_id() is None
True
>>> key_partial = ndb.Key("A", None)
>>> key_partial.integer_id() is None
True
kind()[source]

The kind of the entity referenced.

This comes from the last (kind, id) pair.

>>> key = ndb.Key("Satellite", "Moon", "Space", "Dust")
>>> key.kind()
'Space'
>>>
>>> partial_key = ndb.Key("Known", None)
>>> partial_key.kind()
'Known'
namespace()[source]

The namespace for the key, if set.

>>> key = ndb.Key("A", "B")
>>> key.namespace() is None
True
>>>
>>> key = ndb.Key("A", "B", namespace="rock")
>>> key.namespace()
'rock'
pairs()[source]

The (kind, id) pairs for the key.

>>> key = ndb.Key("Satellite", "Moon", "Space", "Dust")
>>> key.pairs()
(('Satellite', 'Moon'), ('Space', 'Dust'))
>>>
>>> partial_key = ndb.Key("Known", None)
>>> partial_key.pairs()
(('Known', None),)
parent()[source]

Parent key constructed from all but the last (kind, id) pairs.

If there is only one (kind, id) pair, return None.

>>> key = ndb.Key(
...     pairs=[
...         ("Purchase", "Food"),
...         ("Type", "Drink"),
...         ("Coffee", 11),
...     ]
... )
>>> parent = key.parent()
>>> parent
Key('Purchase', 'Food', 'Type', 'Drink')
>>>
>>> grandparent = parent.parent()
>>> grandparent
Key('Purchase', 'Food')
>>>
>>> grandparent.parent() is None
True
project()[source]

The project ID for the key.

Warning

This may differ from the original app passed in to the constructor. This is because prefixed application IDs like s~example are “legacy” identifiers from Google App Engine. They have been replaced by equivalent project IDs, e.g. here it would be example.

>>> key = ndb.Key("A", "B", project="s~example")
>>> key.project()
'example'
>>>
>>> key = ndb.Key("A", "B", project="example")
>>> key.project()
'example'
reference()[source]

The Reference protobuf object for this key.

The return value will be stored on the current key, so the caller promises not to mutate it.

>>> key = ndb.Key("Trampoline", 88, project="xy", namespace="zt")
>>> key.reference()
app: "xy"
path {
  Element {
    type: "Trampoline"
    id: 88
  }
}
name_space: "zt"
root()[source]

The root key.

This is either the current key or the highest parent.

>>> key = ndb.Key("a", 1, "steak", "sauce")
>>> root_key = key.root()
>>> root_key
Key('a', 1)
>>> root_key.root() is root_key
True
serialized()[source]

A Reference protobuf serialized to bytes.

>>> key = ndb.Key("Kind", 1337, project="example")
>>> key.serialized()
b'j\x07exampler\x0b\x0b\x12\x04Kind\x18\xb9\n\x0c'
string_id()[source]

The string ID in the last (kind, id) pair, if any.

>>> key_int = ndb.Key("A", 37)
>>> key_int.string_id() is None
True
>>> key_str = ndb.Key("A", "B")
>>> key_str.string_id()
'B'
>>> key_partial = ndb.Key("A", None)
>>> key_partial.string_id() is None
True
to_legacy_urlsafe(location_prefix)[source]

A urlsafe serialized Reference protobuf with an App Engine prefix.

This will produce a urlsafe string which includes an App Engine location prefix (“partition”), compatible with the Google Datastore admin console.

Parameters

location_prefix (str) – A location prefix (“partition”) to be prepended to the key’s project when serializing the key. A typical value is “s~”, but “e~” or other partitions are possible depending on the project’s region and other factors.

>>> key = ndb.Key("Kind", 1337, project="example")
>>> key.to_legacy_urlsafe("s~")
b'aglzfmV4YW1wbGVyCwsSBEtpbmQYuQoM'
to_old_key()[source]

Convert to an “old”-style datastore key.

See from_old_key() for more information on why this method is not supported.

Raises

NotImplementedError – Always.

urlsafe()[source]

A Reference protobuf serialized and encoded as urlsafe base 64.

>>> key = ndb.Key("Kind", 1337, project="example")
>>> key.urlsafe()
b'agdleGFtcGxlcgsLEgRLaW5kGLkKDA'
google.cloud.ndb.key.UNDEFINED = <object object>

Sentinel value.

Used to indicate a namespace hasn’t been explicitly set in key construction. Used to distinguish between not passing a value and passing None, which indicates the default namespace.