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Entities (Google App Engine API for Java)

com.google.appengine.api.datastore

Class Entities

  • java.lang.Object
    • com.google.appengine.api.datastore.Entities

  • public final class Entities
extends java.lang.Object
    Utility functions and constants for entities.

    • Field Summary

      Fields 
      Modifier and Type Field and Description
      static long ENTITY_GROUP_METADATA_ID
      ID for __entity_group__ entities.
      static java.lang.String ENTITY_GROUP_METADATA_KIND
      A metadata kind that can be used to get information about entity groups.
      static java.lang.String KIND_METADATA_KIND
      A metadata kind that can be used to query for kinds that exist in the datastore.
      static long NAMESPACE_METADATA_EMPTY_ID
      The numeric ID for __namespace__ keys representing the empty namespace.
      static java.lang.String NAMESPACE_METADATA_KIND
      A metadata kind that can be used to query for namespaces that exist in the datastore.
      static java.lang.String PROPERTY_METADATA_KIND
      A metadata kind that can be used to query for properties that exist in the datastore.

    • Constructor Summary

      Constructors 
      Constructor and Description
      Entities() 

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method and Description
      static Key createEntityGroupKey(Key key)
      Create an __entity_group__ key for the entity group containing key.
      static Key createKindKey(java.lang.String kind)
      Create a __kind__ key for kind.
      static Key createNamespaceKey(java.lang.String namespace)
      Create a __namespace__ key for namespace.
      static Key createPropertyKey(java.lang.String kind, java.lang.String property)
      Create a __property__ key for property of kind.
      static java.lang.String getNamespaceFromNamespaceKey(Key namespaceKey)
      Extract the namespace name from a __namespace__ key.
      static long getVersionProperty(Entity entity)
      Get the value of the __version__ property from entity.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • KIND_METADATA_KIND

        public static final java.lang.String KIND_METADATA_KIND
        A metadata kind that can be used to query for kinds that exist in the datastore.
        See Also:
        Constant Field Values

      • PROPERTY_METADATA_KIND

        public static final java.lang.String PROPERTY_METADATA_KIND
        A metadata kind that can be used to query for properties that exist in the datastore.
        See Also:
        Constant Field Values

      • NAMESPACE_METADATA_KIND

        public static final java.lang.String NAMESPACE_METADATA_KIND
        A metadata kind that can be used to query for namespaces that exist in the datastore.
        See Also:
        Constant Field Values

      • NAMESPACE_METADATA_EMPTY_ID

        public static final long NAMESPACE_METADATA_EMPTY_ID
        The numeric ID for __namespace__ keys representing the empty namespace.
        See Also:
        Constant Field Values

      • ENTITY_GROUP_METADATA_KIND

        public static final java.lang.String ENTITY_GROUP_METADATA_KIND
        A metadata kind that can be used to get information about entity groups. The metadata for the entity group with root entity key R is fetched using a DatastoreService.get(com.google.appengine.api.datastore.Key) call on key KeyFactory.createKey(R, ENTITY_GROUP_METADATA_KIND, ENTITY_GROUP_METADATA_ID).

        The resulting entity has a Entity.VERSION_RESERVED_PROPERTY numeric property whose value is guaranteed to increase on every change to the entity group. This value may also occasionally increase without any user-visible change to the entity group.

        See Also:
        Constant Field Values

    • Constructor Detail

      • Entities

        public Entities()

    • Method Detail

      • createKindKey

        public static Key createKindKey(java.lang.String kind)
        Create a __kind__ key for kind.
        Parameters:
        kind - Kind to create key for.
        Returns:
        __kind__ key.

      • createPropertyKey

        public static Key createPropertyKey(java.lang.String kind,
                                    java.lang.String property)
        Create a __property__ key for property of kind.
        Parameters:
        kind - Kind to create key for.
        property - Property to create key for.
        Returns:
        __property__ key.

      • createNamespaceKey

        public static Key createNamespaceKey(java.lang.String namespace)
        Create a __namespace__ key for namespace.
        Parameters:
        namespace - Namespace to create key for.
        Returns:
        __namespace__ key.

      • getNamespaceFromNamespaceKey

        public static java.lang.String getNamespaceFromNamespaceKey(Key namespaceKey)
        Extract the namespace name from a __namespace__ key.
        Parameters:
        namespaceKey - Key to extract namespace from.
        Returns:
        The namespace name.

      • createEntityGroupKey

        public static Key createEntityGroupKey(Key key)
        Create an __entity_group__ key for the entity group containing key.
        Parameters:
        key - Key of any entity in the entity group.
        Returns:
        __entity_group__ key.

      • getVersionProperty

        public static long getVersionProperty(Entity entity)
        Get the value of the __version__ property from entity.
        Parameters:
        entity - Entity to fetch __version__ from (must have a numeric __version__ property).
        Returns:
        __version__ property value.