com.google.appengine.api.datastore
Class Entity

java.lang.Object
  extended by com.google.appengine.api.datastore.PropertyContainer
      extended by com.google.appengine.api.datastore.Entity
All Implemented Interfaces:
java.io.Serializable, java.lang.Cloneable

public final class Entity
extends PropertyContainer
implements java.lang.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
static java.lang.String KEY_RESERVED_PROPERTY
          A reserved property name used to refer to the key of the entity.
static java.lang.String SCATTER_RESERVED_PROPERTY
          A reserved property name used to refer to the scatter property of the entity.
static java.lang.String VERSION_RESERVED_PROPERTY
          A reserved property name used to report an entity group's version.
 
Constructor Summary
Entity(Key key)
          Create a new Entity uniquely identified by the provided Key.
Entity(java.lang.String kind)
          Create a new Entity with the specified kind and no parent Entity.
Entity(java.lang.String kind, Key parent)
          Create a new Entity with the specified kind and parent Entity.
Entity(java.lang.String kind, long id)
          Create a new Entity with the specified kind and ID and no parent Entity.
Entity(java.lang.String kind, long id, Key parent)
          Create a new Entity with the specified kind and ID and parent Entity.
Entity(java.lang.String kind, java.lang.String keyName)
          Create a new Entity with the specified kind and key name and no parent Entity.
Entity(java.lang.String kind, java.lang.String keyName, Key parent)
          Create a new Entity with the specified kind, key name, and parent Entity.
 
Method Summary
 Entity clone()
          Returns a shallow copy of this Entity instance.
 boolean equals(java.lang.Object object)
          Two Entity objects are considered equal if they refer to the same entity (i.e.
 java.lang.String getAppId()
          Returns the identifier of the application that owns this Entity.
 Key getKey()
          Returns the Key that represents this Entity.
 java.lang.String getKind()
          Returns a logical type that is associated with this Entity.
 java.lang.String getNamespace()
          Returns the namespace of the application/namespace that owns this Entity.
 Key getParent()
          Get a Key that corresponds to this the parent Entity of this Entity.
 int hashCode()
           
 void setPropertiesFrom(Entity src)
           
 java.lang.String toString()
           
 
Methods inherited from class com.google.appengine.api.datastore.PropertyContainer
getProperties, getProperty, hasProperty, isUnindexedProperty, removeProperty, setPropertiesFrom, setProperty, setUnindexedProperty
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

KEY_RESERVED_PROPERTY

public static final java.lang.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 java.lang.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 java.lang.String VERSION_RESERVED_PROPERTY
A reserved property name used to report an entity group's version.

See Also:
Constant Field Values
Constructor Detail

Entity

public Entity(java.lang.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(java.lang.String kind,
              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(java.lang.String kind,
              java.lang.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(java.lang.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(java.lang.String kind,
              java.lang.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(java.lang.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 Detail

equals

public boolean equals(java.lang.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 java.lang.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 java.lang.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 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 java.lang.Object

toString

public java.lang.String toString()
Overrides:
toString in class java.lang.Object

getAppId

public java.lang.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 java.lang.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)