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Neo4j kernel is a lightweight, embedded Java database designed to
store data structured as graphs rather than tables. For more
information, see http://neo4j.org.
/**
* Copyright (c) 2002-2013 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see
*
* @param the type of entity created by this {@link UniqueFactory}.
*/
public abstract class UniqueFactory
{
/**
* Implementation of {@link UniqueFactory} for {@link Node}.
*
* @author Tobias Lindaaker
*/
public static abstract class UniqueNodeFactory extends UniqueFactory
{
/**
* Create a new {@link UniqueFactory} for nodes.
*
* @param index the index to store entities uniquely in.
*/
public UniqueNodeFactory( Index index )
{
super( index );
}
/**
* Create a new {@link UniqueFactory} for nodes.
*
* @param graphdb the graph database to get the index from.
* @param index the name of the index to store entities uniquely in.
*/
public UniqueNodeFactory( GraphDatabaseService graphdb, String index )
{
super( graphdb.index().forNodes( index ) );
}
/**
* Default implementation of {@link UniqueFactory#create(Map)}, creates a plain node. Override to
* retrieve the node to add to the index by some other means than by creating it. For initialization of the
* {@link Node}, use the {@link UniqueFactory#initialize(PropertyContainer, Map)} method.
*
* @see UniqueFactory#create(Map)
* @see UniqueFactory#initialize(PropertyContainer, Map)
*/
@Override
protected Node create( Map properties )
{
return graphDatabase().createNode();
}
/**
* Default implementation of {@link UniqueFactory#delete(PropertyContainer)}. Invokes
* {@link Node#delete()}.
*
* @see UniqueFactory#delete(PropertyContainer)
*/
@Override
protected void delete( Node node )
{
node.delete();
}
}
/**
* Implementation of {@link UniqueFactory} for {@link Relationship}.
*
* @author Tobias Lindaaker
*/
public static abstract class UniqueRelationshipFactory extends UniqueFactory
{
/**
* Create a new {@link UniqueFactory} for relationships.
*
* @param index the index to store entities uniquely in.
*/
public UniqueRelationshipFactory( Index index )
{
super( index );
}
/**
* Create a new {@link UniqueFactory} for relationships.
*
* @param graphdb the graph database to get the index from.
* @param index the name of the index to store entities uniquely in.
*/
public UniqueRelationshipFactory( GraphDatabaseService graphdb, String index )
{
super( graphdb.index().forRelationships( index ) );
}
/**
* Default implementation of {@link UniqueFactory#initialize(PropertyContainer, Map)}, does nothing
* for {@link Relationship Relationships}. Override to perform some action with the guarantee that this method
* is only invoked for the transaction that succeeded in creating the {@link Relationship}.
*
* @see UniqueFactory#initialize(PropertyContainer, Map)
* @see UniqueFactory#create(Map)
*/
@Override
protected void initialize( Relationship relationship, Map properties )
{
// this class has the create() method, initialize() is optional
}
/**
* Default implementation of {@link UniqueFactory#delete(PropertyContainer)}. Invokes
* {@link Relationship#delete()}.
*
* @see UniqueFactory#delete(PropertyContainer)
*/
@Override
protected void delete( Relationship relationship )
{
relationship.delete();
}
}
/**
* Implement this method to create the {@link Node} or {@link Relationship} to index.
*
* This method will be invoked exactly once per transaction that attempts to create an entry in the index.
* The created entity might be discarded if another thread creates an entity with the same mapping concurrently.
*
* @param properties the properties that this entity will is to be indexed uniquely with.
* @return the entity to add to the index.
*/
protected abstract T create( Map properties );
/**
* Implement this method to initialize the {@link Node} or {@link Relationship} created for being stored in the index.
*
* This method will be invoked exactly once per created unique entity.
*
* The created entity might be discarded if another thread creates an entity concurrently.
* This method will however only be invoked in the transaction that succeeds in creating the node.
*
* @param created the created entity to initialize.
* @param properties the properties that this entity was indexed uniquely with.
*/
protected abstract void initialize( T created, Map properties );
/**
* Invoked after a new entity has been {@link #create(Map) created}, but adding it to the index failed (due to being
* added by another transaction concurrently). The purpose of this method is to undo the {@link #create(Map)
* creation of the entity}, the default implementations of this method remove the entity. Override this method to
* define a different behavior.
*
* @param created the entity that was created but was not added to the index.
*/
protected abstract void delete( T created );
/**
* Get the indexed entity, creating it (exactly once) if no indexed entity exists.
* @param key the key to find the entity under in the index.
* @param value the value the key is mapped to for the entity in the index.
* @return the unique entity in the index.
*/
public final T getOrCreate( String key, Object value )
{
T result = index.get( key, value ).getSingle();
if ( result == null )
{
Transaction tx = graphDatabase().beginTx();
try
{
Map properties = Collections.singletonMap( key, value );
T created = create( properties );
result = index.putIfAbsent( created, key, value );
if ( result == null )
{
initialize( created, properties );
result = created;
}
else
{
delete( created );
}
tx.success();
}
finally
{
tx.finish();
}
}
return result;
}
/**
* Get the {@link GraphDatabaseService graph database} of the referenced index.
* @return the {@link GraphDatabaseService graph database} of the referenced index.
*/
protected final GraphDatabaseService graphDatabase()
{
return index.getGraphDatabase();
}
/**
* Get the referenced index.
* @return the referenced index.
*/
protected final Index index()
{
return index;
}
private final Index index;
private UniqueFactory( Index index )
{
this.index = index;
}
}
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