com.google.appengine.api.datastore
Class Entity

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

public final class Entity
extends java.lang.Object
implements java.io.Serializable

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.
 
Constructor Summary
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, 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
 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.
 Key getParent()
          Get a Key that corresponds to this the parent Entity of this Entity.
 java.util.Map<java.lang.String,java.lang.Object> getProperties()
          Gets all of the properties belonging to this Entity.
 java.lang.Object getProperty(java.lang.String propertyName)
          Gets the property with the specified name.
 int hashCode()
           
 boolean hasProperty(java.lang.String propertyName)
          Returns true if a property has been set.
 void removeProperty(java.lang.String propertyName)
          Removes any property with the specified name.
 void setProperty(java.lang.String propertyName, java.lang.Object value)
          Sets the property named, propertyName, to value.
 java.lang.String toString()
           
 
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
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.


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.

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.


getProperty

public java.lang.Object getProperty(java.lang.String propertyName)
Gets the property with the specified name. The value returned may not be the same type as originally set via setProperty(java.lang.String, java.lang.Object).

Returns:
the property corresponding to propertyName.

getProperties

public java.util.Map<java.lang.String,java.lang.Object> getProperties()
Gets all of the properties belonging to this Entity.

Returns:
an unomdifiable Map of properties.

hashCode

public int hashCode()
Overrides:
hashCode in class java.lang.Object

hasProperty

public boolean hasProperty(java.lang.String propertyName)
Returns true if a property has been set. This function can be used to test if a property has been specifically set to null.

Returns:
true iff the property named propertyName exists.

removeProperty

public void removeProperty(java.lang.String propertyName)
Removes any property with the specified name. If there is no property with this name set, simply does nothing.

Throws:
java.lang.NullPointerException - If propertyName is null.

setProperty

public void setProperty(java.lang.String propertyName,
                        java.lang.Object value)
Sets the property named, propertyName, to value.

As the value is stored in the datastore, it is converted to the datastore's native type. This may include widening, such as converting a Short to a Long.

All Collections are prone to losing their sort order and their original types as they are stored in the datastore. For example, a TreeSet may be returned as a List from getProperty(java.lang.String), with an arbitrary re-ordering of elements.

Parameters:
value - may be one of the supported datatypes, or a heterogenous Collection of one of the supported datatypes.
Throws:
java.lang.IllegalArgumentException - If the value is not of a type that the data store supports.

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.