public final class Key extends java.lang.Object implements java.io.Serializable, java.lang.Comparable<Key>
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(java.lang.String, long)
or getChild(java.lang.String, long)
.
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.
KeyFactory
,
Serialized FormModifier and Type | Method and Description |
---|---|
int |
compareTo(Key other)
Compares two
Key objects. |
boolean |
equals(java.lang.Object object)
Compares two
Key objects by comparing ids, kinds, parent and appIdNamespace. |
java.lang.String |
getAppId()
Returns the appId for this
Key . |
Key |
getChild(java.lang.String kind,
long id)
Creates a new key having
this as parent and the given numeric identifier. |
Key |
getChild(java.lang.String kind,
java.lang.String name)
Creates a new key having
this as parent and the given name. |
long |
getId()
Returns the numeric identifier of this
Key . |
java.lang.String |
getKind()
Returns the kind of the
Entity represented by this Key . |
java.lang.String |
getName()
Returns the name of this
Key . |
java.lang.String |
getNamespace()
Returns the namespace for this
Key . |
Key |
getParent()
If this
Key has a parent, return a Key that represents it. |
int |
hashCode() |
boolean |
isComplete()
Returns true if this Key has a name specified or has been assigned an identifier.
|
java.lang.String |
toString() |
public java.lang.String getKind()
Entity
represented by this Key
.public Key getParent()
Key
has a parent, return a Key
that represents it. If not, simply
return null.public int hashCode()
hashCode
in class java.lang.Object
public java.lang.String toString()
toString
in class java.lang.Object
public boolean equals(java.lang.Object object)
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.equals
in class java.lang.Object
public java.lang.String getAppId()
Key
.public java.lang.String getNamespace()
Key
.public long getId()
Key
.public java.lang.String getName()
Key
.public Key getChild(java.lang.String kind, long id)
this
as parent and the given numeric identifier. The parent
key must be complete.kind
- the kind of the child key to createid
- the numeric identifier of the key in kind
, unique for this parentpublic Key getChild(java.lang.String kind, java.lang.String name)
this
as parent and the given name. The parent key must be
complete.kind
- the kind of the child key to createname
- the name of the key in kind
, as an arbitrary string unique for this parentpublic boolean isComplete()
public int compareTo(Key other)
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.
compareTo
in interface java.lang.Comparable<Key>