Class Key (2.0.0)

public final class Key implements Serializable, Comparable<Key>

The primary key for a datastore entity.

A datastore GUID. A Key instance uniquely identifies an entity across all apps, and includes all information necessary to fetch the entity from the datastore with DatastoreService.get(Key).

You can create Key objects directly by using KeyFactory#createKey or #getChild.

You can also retrieve the Key automatically created when you create a new Entity, or serialize Key objects, or use KeyFactory to convert them to and from websafe String values. See Also: KeyFactory

Inheritance

java.lang.Object > Key

Methods

compareTo(Key other)

public int compareTo(Key other)

Compares two Key objects. The algorithm proceeds as follows: Turn each Key into an iterator where the first element returned is the top-most ancestor, the next element is the child of the previous element, and so on. The last element will be the Key we started with. Once we have assembled these two iterators (one for 'this' and one for the Key we're comparing to), consume them in parallel, comparing the next element from each iterator. If at any point the comparison of these two elements yields a non-zero result, return that as the result of the overall comparison. If we exhaust the iterator built from 'this' before we exhaust the iterator built from the other Key, we return less than. An example:

app1.type1.4.app1.type2.9 < app1.type1.4.app1.type2.9.app1.type3.2

If we exhaust the iterator built from the other Key before we exhaust the iterator built from 'this', we return greater than. An example:

app1.type1.4.app1.type2.9.app1.type3.2 > app1.type1.4.app1.type2.9

The relationship between individual Key Keys is performed by comparing app followed by kind followed by id. If both keys are assigned names rather than ids, compares names instead of ids. If neither key has an id or a name we return an arbitrary but consistent result. Assuming all other components are equal, all ids are less than all names.

Parameter
Name Description
other Key
Returns
Type Description
int

equals(@Nullable Object object)

public boolean equals(@Nullable Object object)

Compares two Key objects by comparing ids, kinds, parent and appIdNamespace. If both keys are assigned names rather than ids, compares names instead of ids. If neither key has an id or a name, the keys are only equal if they reference the same object.

Parameter
Name Description
object @org.checkerframework.checker.nullness.qual.Nullable java.lang.Object
Returns
Type Description
boolean
Overrides

getAppId()

public String getAppId()

Returns the appId for this Key.

Returns
Type Description
String

getChild(String kind, String name)

public Key getChild(String kind, String name)

Creates a new key having this as parent and the given name. The parent key must be complete.

Parameters
Name Description
kind String

the kind of the child key to create

name String

the name of the key in kind, as an arbitrary string unique for this parent

Returns
Type Description
Key

getChild(String kind, long id)

public Key getChild(String kind, long id)

Creates a new key having this as parent and the given numeric identifier. The parent key must be complete.

Parameters
Name Description
kind String

the kind of the child key to create

id long

the numeric identifier of the key in kind, unique for this parent

Returns
Type Description
Key

getId()

public long getId()

Returns the numeric identifier of this Key.

Returns
Type Description
long

getKind()

public String getKind()

Returns the kind of the Entity represented by this Key.

Returns
Type Description
String

getName()

public @Nullable String getName()

Returns the name of this Key.

Returns
Type Description
@org.checkerframework.checker.nullness.qual.Nullable java.lang.String

getNamespace()

public String getNamespace()

Returns the namespace for this Key.

Returns
Type Description
String

getParent()

public @Nullable Key getParent()

If this Key has a parent, return a Key that represents it. If not, simply return null.

Returns
Type Description
@org.checkerframework.checker.nullness.qual.Nullable com.google.appengine.api.datastore.Key

hashCode()

public int hashCode()
Returns
Type Description
int
Overrides

isComplete()

public boolean isComplete()

Returns true if this Key has a name specified or has been assigned an identifier.

Returns
Type Description
boolean

toString()

public String toString()
Returns
Type Description
String
Overrides