Package com.googlecode.objectify

Class Ref<T>

java.lang.Object
com.googlecode.objectify.Ref<T>
All Implemented Interfaces:
Serializable, Comparable<Ref<T>>
Direct Known Subclasses:
DeadRef, LiveRef
public abstract class Ref<T>
extends Object
implements Serializable, Comparable<Ref<T>>

Ref is a Key which allows the entity value to be fetched directly.

Note that the methods might or might not throw runtime exceptions related to datastore operations; ConcurrentModificationException, DatastoreTimeoutException, DatastoreFailureException, and DatastoreNeedIndexException. Some Refs hide datastore operations that could throw these exceptions.

Author:
Jeff Schnitzer
See Also:
Serialized Form

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    protected Key<T>
    key
    The key associated with this ref

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    Ref()
    For GWT serialization
    protected
    Ref​(Key<T> key)
    Create a Ref based on the key, with the specified session

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    compareTo​(Ref<T> o)
    Comparison is based on key
    static <T> Ref<T>
    create​(Key<T> key)
    Key.create(Blah.class, id) is easier to type than new Key(Blah.class, id)
    static <T> Ref<T>
    create​(T value)
    Creates a Ref from a registered pojo entity
    boolean
    equals​(Object obj)
    Equality comparison is based on key equivalence
    boolean
    equivalent​(Key<T> other)
    Type safe comparison for key equivalence
    boolean
    equivalent​(Ref<T> other)
    Type-safe comparison for key equivalence
    abstract T
    get()
    Obtain the entity value associated with the key.
    Key<T>
    getKey()
    Same as key() but conforms to JavaBeans conventions in case this is being processed by a JSON converter or expression language.
    T
    getValue()
    This method exists to facilitate serialization via javabeans conventions.
    int
    hashCode()
    Hash code is simply that of key
    abstract boolean
    isLoaded()
    If an entity has been loaded into the session or is otherwise available, this will return true.
    Key<T>
    key()
     
    T
    safe()
    Obtain the entity value, throwing an exception if the entity was not found.
    String
    toString()
    Renders some info about the key

    Methods inherited from class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

  • Field Details

    • key

      protected Key<T> key
      The key associated with this ref

  • Constructor Details

    • Ref

      protected Ref()
      For GWT serialization

    • Ref

      protected Ref​(Key<T> key)
      Create a Ref based on the key, with the specified session

  • Method Details

    • create

      public static <T> Ref<T> create​(Key<T> key)
      Key.create(Blah.class, id) is easier to type than new Key(Blah.class, id)

    • create

      public static <T> Ref<T> create​(T value)
      Creates a Ref from a registered pojo entity

    • key

      public Key<T> key()
      Returns:
      the key associated with this Ref

    • get

      public abstract T get()
      Obtain the entity value associated with the key. Will pull from session if present, otherwise will fetch from the datastore.
      Returns:
      the entity referenced, or null if the entity was not found

    • isLoaded

      public abstract boolean isLoaded()
      If an entity has been loaded into the session or is otherwise available, this will return true. Calls to get() will not require a trip to backing store. Note that even when loaded, get() can still return null if there is no entity which corresponds to the key.
      Returns:
      true if the value is in the session or otherwise immediately available; false if get() will require a trip to the datastore or memcache.

    • getValue

      public final T getValue()
      This method exists to facilitate serialization via javabeans conventions. Unlike get(), it will return null if isLoaded() is false.
      Returns:
      the entity referenced, or null if either the entity was not found or isLoaded() is false.

    • getKey

      public final Key<T> getKey()
      Same as key() but conforms to JavaBeans conventions in case this is being processed by a JSON converter or expression language.

    • safe

      public final T safe() throws NotFoundException
      Obtain the entity value, throwing an exception if the entity was not found.
      Returns:
      the entity referenced. Never returns null.
      Throws:
      NotFoundException - if the specified entity was not found

    • compareTo

      public int compareTo​(Ref<T> o)
      Comparison is based on key
      Specified by:
      compareTo in interface Comparable<T>

    • equals

      public boolean equals​(Object obj)
      Equality comparison is based on key equivalence
      Overrides:
      equals in class Object

    • equivalent

      public boolean equivalent​(Ref<T> other)
      Type-safe comparison for key equivalence

    • equivalent

      public boolean equivalent​(Key<T> other)
      Type safe comparison for key equivalence

    • hashCode

      public int hashCode()
      Hash code is simply that of key
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Renders some info about the key
      Overrides:
      toString in class Object