Package com.google.appengine.api.datastore

Class Entity

java.lang.Object

com.google.appengine.api.datastore.PropertyContainer

com.google.appengine.api.datastore.Entity

All Implemented Interfaces:

Serializable, Cloneable

public final class Entity
extends PropertyContainer
implements Cloneable

Entity is the fundamental unit of data storage. It has an immutable identifier (contained in the Key) object, a reference to an optional parent Entity, a kind (represented as an arbitrary string), and a set of zero or more typed properties.

See Also:

• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
static final String	KEY_RESERVED_PROPERTY	A reserved property name used to refer to the key of the entity.
static final String	SCATTER_RESERVED_PROPERTY	A reserved property name used to refer to the scatter property of the entity.
static final String	VERSION_RESERVED_PROPERTY	A reserved property name used to report an entity group's version.

Constructor Summary

Constructors

Constructor	Description
Entity(Key key)	Create a new Entity uniquely identified by the provided Key.
Entity(String kind)	Create a new Entity with the specified kind and no parent Entity.
Entity(String kind, long id)	Create a new Entity with the specified kind and ID and no parent Entity.
Entity(String kind, long id, Key parent)	Create a new Entity with the specified kind and ID and parent Entity.
Entity(String kind, @Nullable Key parent)	Create a new Entity with the specified kind and parent Entity.
Entity(String kind, String keyName)	Create a new Entity with the specified kind and key name and no parent Entity.
Entity(String kind, String keyName, Key parent)	Create a new Entity with the specified kind, key name, and parent Entity.

Method Summary

Modifier and Type	Method	Description
Entity	clone()	Returns a shallow copy of this Entity instance.
boolean	equals(@Nullable Object object)	Two Entity objects are considered equal if they refer to the same entity (i.e. their Key objects match).
String	getAppId()	Returns the identifier of the application that owns this Entity.
Key	getKey()	Returns the Key that represents this Entity.
String	getKind()	Returns a logical type that is associated with this Entity.
String	getNamespace()	Returns the namespace of the application/namespace that owns this Entity.
@Nullable Key	getParent()	Get a Key that corresponds to this the parent Entity of this Entity.
int	hashCode()
void	setPropertiesFrom(Entity src)
String	toString()

Methods inherited from class com.google.appengine.api.datastore.PropertyContainer

getProperties, getProperty, hasProperty, isUnindexedProperty, removeProperty, setIndexedProperty, setPropertiesFrom, setProperty, setUnindexedProperty

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Details

KEY_RESERVED_PROPERTY

public static final String KEY_RESERVED_PROPERTY

A reserved property name used to refer to the key of the entity. This string can be used for filtering and sorting by the entity key itself.

See Also:

• Constant Field Values

SCATTER_RESERVED_PROPERTY

public static final String SCATTER_RESERVED_PROPERTY

A reserved property name used to refer to the scatter property of the entity. Used for finding split points (e.g. for mapping over a kind).

See Also:

• Constant Field Values

VERSION_RESERVED_PROPERTY

public static final String VERSION_RESERVED_PROPERTY

A reserved property name used to report an entity group's version.

See Also:

• Constant Field Values

Constructor Details

Entity

public Entity(String kind)

Create a new Entity with the specified kind and no parent Entity. The instantiated Entity will have an incomplete Key when this constructor returns. The Key will remain incomplete until you put the Entity, after which time the Key will have its id set.

Entity

public Entity(String kind,
 @Nullable Key parent)

Create a new Entity with the specified kind and parent Entity. The instantiated Entity will have an incomplete Key when this constructor returns. The Key will remain incomplete until you put the Entity, after which time the Key will have its id set.

Entity

public Entity(String kind,
 String keyName)

Create a new Entity with the specified kind and key name and no parent Entity. The instantiated Entity will have a complete Key when this constructor returns. The Key's name field will be set to the value of keyName.

This constructor is syntactic sugar for new Entity(KeyFactory.createKey(kind, keyName)).

Entity

public Entity(String kind,
 long id)

Create a new Entity with the specified kind and ID and no parent Entity. The instantiated Entity will have a complete Key when this constructor returns. The Key's id field will be set to the value of id.

Creating an entity for the purpose of insertion (as opposed to update) with this constructor is discouraged unless the id was obtained from a key returned by a KeyRange obtained from AsyncDatastoreService.allocateIds(String, long) or DatastoreService.allocateIds(String, long) for the same kind.

This constructor is syntactic sugar for new Entity(KeyFactory.createKey(kind, id)).

Entity

public Entity(String kind,
 String keyName,
 Key parent)

Create a new Entity with the specified kind, key name, and parent Entity. The instantiated Entity will have a complete Key when this constructor returns. The Key's name field will be set to the value of keyName.

This constructor is syntactic sugar for new Entity(KeyFactory.createKey(parent, kind, keyName)).

Entity

public Entity(String kind,
 long id,
 Key parent)

Create a new Entity with the specified kind and ID and parent Entity. The instantiated Entity will have a complete Key when this constructor returns. The Key's id field will be set to the value of id.

Creating an entity for the purpose of insertion (as opposed to update) with this constructor is discouraged unless the id was obtained from a key returned by a KeyRange obtained from AsyncDatastoreService.allocateIds(Key, String, long) or DatastoreService.allocateIds(Key, String, long) for the same parent and kind.

This constructor is syntactic sugar for new Entity(KeyFactory.createKey(parent, kind, id)).

Entity

public Entity(Key key)

Create a new Entity uniquely identified by the provided Key. Creating an entity for the purpose of insertion (as opposed to update) with a key that has its id field set is strongly discouraged unless the key was returned by a KeyRange.

See Also:

• KeyRange

Method Details

equals

public boolean equals(@Nullable Object object)

Two Entity objects are considered equal if they refer to the same entity (i.e. their Key objects match).

Overrides:

equals in class Object

getKey

public Key getKey()

Returns the Key that represents this Entity. If the entity has not yet been saved (e.g. via DatastoreService.put), this Key will not be fully specified and cannot be used for certain operations (like DatastoreService.get). Once the Entity has been saved, its Key will be updated to be fully specified.

getKind

public String getKind()

Returns a logical type that is associated with this Entity. This is simply a convenience method that forwards to the Key for this Entity.

getParent

public @Nullable Key getParent()

Get a Key that corresponds to this the parent Entity of this Entity. This is simply a convenience method that forwards to the Key for this Entity.

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

getAppId

public String getAppId()

Returns the identifier of the application that owns this Entity. This is simply a convenience method that forwards to the Key for this Entity.

getNamespace

public String getNamespace()

Returns the namespace of the application/namespace that owns this Entity. This is simply a convenience method that forwards to the Key for this Entity.

clone

public Entity clone()

Returns a shallow copy of this Entity instance. Collection properties are cloned as an ArrayList, the type returned from the datastore. Instances of mutable datastore types are cloned as well. Instances of all other types are reused.

Returns:

a shallow copy of this Entity

setPropertiesFrom

public void setPropertiesFrom(Entity src)