Module org.eclipse.persistence.core
Package org.eclipse.persistence.internal.indirection

Class DatabaseValueHolder<T>

java.lang.Object
org.eclipse.persistence.internal.indirection.DatabaseValueHolder<T>
All Implemented Interfaces:
Serializable, Cloneable, ValueHolderInterface<T>, WeavedAttributeValueHolderInterface<T>
Direct Known Subclasses:
BackupValueHolder, CacheBasedValueHolder, ProtectedValueHolder, QueryBasedValueHolder, RemoteValueHolder, TransformerBasedValueHolder, UnitOfWorkValueHolder
public abstract class DatabaseValueHolder<T> extends Object implements WeavedAttributeValueHolderInterface<T>, Cloneable, Serializable
DatabaseValueHolder wraps a database-stored object and implements behavior to access it. The object is read only once from database after which is cached for faster access.
See Also:

  • Field Details

    • value

      protected volatile T value
      Stores the object after it is read from the database.

    • isInstantiated

      protected volatile boolean isInstantiated
      Indicates whether the object has been read from the database or not.

    • session

      protected transient AbstractSession session
      Stores the session for the database that contains the object.

    • row

      protected AbstractRecord row
      Stores the row representation of the object.

    • isCoordinatedWithProperty

      protected boolean isCoordinatedWithProperty
      The variable below is used as part of the implementation of WeavedAttributeValueHolderInterface It is used to track whether a valueholder that has been weaved into a class is coordinated with the underlying property Set internally in EclipseLink when the state of coordination between a weaved valueholder and the underlying property is known

  • Constructor Details

    • DatabaseValueHolder

      protected DatabaseValueHolder()
      Default constructor.

  • Method Details

    • clone

      public Object clone()
      Description copied from interface: ValueHolderInterface
      PUBLIC: Copy the value holder (but not its' reference, shallow).
      Specified by:
      clone in interface ValueHolderInterface<T>
      Overrides:
      clone in class Object

    • getRow

      public AbstractRecord getRow()
      Return the row.

    • getSession

      public AbstractSession getSession()
      Return the session.

    • getWrappedValueHolder

      public ValueHolderInterface<?> getWrappedValueHolder()

    • getValue

      public T getValue()
      Return the object.
      Specified by:
      getValue in interface ValueHolderInterface<T>

    • getValue

      public T getValue(UnitOfWorkImpl uow)
      Process against the UOW and attempt to load a local copy before going to the shared cache If null is returned then the calling UOW will instantiate as normal.

    • instantiate

      protected abstract T instantiate() throws DatabaseException
      Instantiate the object.
      Throws:
      DatabaseException

    • instantiateForUnitOfWorkValueHolder

      public abstract T instantiateForUnitOfWorkValueHolder(UnitOfWorkValueHolder<T> unitOfWorkValueHolder)
      Triggers UnitOfWork valueholders directly without triggering the wrapped valueholder (this).

      When in transaction and/or for pessimistic locking the UnitOfWorkValueHolder needs to be triggered directly without triggering the wrapped valueholder. However only the wrapped valueholder knows how to trigger the indirection, i.e. it may be a batchValueHolder, and it stores all the info like the row and the query. Note: Implementations of this method are not necessarily thread-safe. They must be used in a synchronized manner

    • isCoordinatedWithProperty

      public boolean isCoordinatedWithProperty()
      This method is used as part of the implementation of WeavedAttributeValueHolderInterface It is used to check whether a valueholder that has been weaved into a class is coordinated with the underlying property
      Specified by:
      isCoordinatedWithProperty in interface WeavedAttributeValueHolderInterface<T>

    • isNewlyWeavedValueHolder

      public boolean isNewlyWeavedValueHolder()
      This method is used as part of the implementation of WeavedAttributeValueHolderInterface. A DatabaseValueHolder is set up by TopLink and will never be a newly weaved valueholder. As a result, this method is stubbed out.
      Specified by:
      isNewlyWeavedValueHolder in interface WeavedAttributeValueHolderInterface<T>

    • isEasilyInstantiated

      public boolean isEasilyInstantiated()
      INTERNAL: Answers if this valueholder is easy to instantiate.
      Returns:
      true if getValue() won't trigger a database read.

    • isInstantiated

      public boolean isInstantiated()
      Return a boolean indicating whether the object has been read from the database or not.
      Specified by:
      isInstantiated in interface ValueHolderInterface<T>

    • isPessimisticLockingValueHolder

      public abstract boolean isPessimisticLockingValueHolder()
      Answers if this valueholder is a pessimistic locking one. Such valueholders are special in that they can be triggered multiple times by different UnitsOfWork. Each time a lock query will be issued. Hence even if instantiated it may have to be instantiated again, and once instantiated all fields can not be reset. Note: Implementations of this method are not necessarily thread-safe. They must be used in a synchronizaed manner

    • isTransactionalValueHolder

      protected boolean isTransactionalValueHolder()
      Answers if this valueholder is referenced only by a UnitOfWork valueholder. I.e. it was built in valueFromRow which was called by buildCloneFromRow.

      Sometimes in transaction a UnitOfWork clone, and all valueholders, are built directly from the row; however a UnitOfWorkValueHolder does not know how to instantiate itself so wraps this which does.

      On a successful merge must be released to the session cache with releaseWrappedValueHolder.

    • isSerializedRemoteUnitOfWorkValueHolder

      public boolean isSerializedRemoteUnitOfWorkValueHolder()
      Used to determine if this is a remote uow value holder that was serialized to the server. It has no reference to its wrapper value holder, so must find its original object to be able to instantiate.

    • postInstantiate

      public void postInstantiate()
      INTERNAL: Run any extra code required after the valueholder instantiates
      See Also:

    • privilegedSetValue

      public void privilegedSetValue(T value)
      Set the object. This is used only by the privileged methods. One must be very careful in using this method.

    • releaseWrappedValueHolder

      public void releaseWrappedValueHolder(AbstractSession targetSession)
      Releases a wrapped valueholder privately owned by a particular unit of work.

      When unit of work clones are built directly from rows no object in the shared cache points to this valueholder, so it can store the unit of work as its session. However once that UnitOfWork commits and the valueholder is merged into the shared cache, the session needs to be reset to the root session, ie. the server session.

    • resetFields

      protected void resetFields()
      Reset all the fields that are not needed after instantiation.

    • setIsCoordinatedWithProperty

      public void setIsCoordinatedWithProperty(boolean coordinated)
      This method is used as part of the implementation of WeavedAttributeValueHolderInterface It is used internally by EclipseLink to set whether a valueholder that has been weaved into a class is coordinated with the underlying property
      Specified by:
      setIsCoordinatedWithProperty in interface WeavedAttributeValueHolderInterface<T>

    • setIsNewlyWeavedValueHolder

      public void setIsNewlyWeavedValueHolder(boolean isNew)
      This method is used as part of the implementation of WeavedAttributeValueHolderInterface A DatabaseValueHolder is set up by EclipseLink and will never be a newly weaved valueholder As a result, this method is stubbed out.
      Specified by:
      setIsNewlyWeavedValueHolder in interface WeavedAttributeValueHolderInterface<T>

    • setInstantiated

      public void setInstantiated()
      Set the instantiated flag to true.

    • setRow

      public void setRow(AbstractRecord row)
      Set the row.

    • setSession

      public void setSession(AbstractSession session)
      Set the session.

    • setUninstantiated

      public void setUninstantiated()
      Set the instantiated flag to false.

    • setValue

      public void setValue(T value)
      Set the object.
      Specified by:
      setValue in interface ValueHolderInterface<T>

    • shouldAllowInstantiationDeferral

      public boolean shouldAllowInstantiationDeferral()
      INTERNAL: Return if add/remove should trigger instantiation or avoid. Current instantiation is avoided is using change tracking.
      Specified by:
      shouldAllowInstantiationDeferral in interface WeavedAttributeValueHolderInterface<T>

    • toString

      public String toString()
      Overrides:
      toString in class Object