java - 使用 graphdb 在节点之间建立关系

Question

我对 graph-db 非常陌生，现在我正在尝试使用示例来了解它的基础知识。下面是我尝试过的示例代码，我试图在三个节点之间建立关系。我正在尝试将以下内容作为 o/p。

我的代码

        private static final String DB_PATH = "/home/nnn/Documents/softwares/neo4j-community-2.0.1";

public String greeting;


GraphDatabaseService graphDb;
Node firstNode;
Node secondNode;
Node thirdNode;

Relationship relationship;

private static enum RelTypes implements RelationshipType
{
    LIKES
}

public static void main( final String[] args )
{
    G1 hello = new G1();
    hello.createDb();
    hello.removeData();
    hello.shutDown();
}

void createDb()
{
    clearDb();

    graphDb = new GraphDatabaseFactory().newEmbeddedDatabase( DB_PATH );
    registerShutdownHook( graphDb );

    try ( Transaction tx = graphDb.beginTx() )
    {

        firstNode = graphDb.createNode();
        firstNode.setProperty( "message", "Alice " );
        secondNode = graphDb.createNode();
        secondNode.setProperty( "message", "Bob" );
        thirdNode = graphDb.createNode();
        thirdNode.setProperty( "message", "Anu" );

        relationship = firstNode.createRelationshipTo( secondNode, RelTypes.LIKES);
        relationship.setProperty( "message", "likes " );

        relationship = firstNode.createRelationshipTo( thirdNode, RelTypes.LIKES);
        relationship.setProperty( "message", "likes " );

        System.out.print( firstNode.getProperty("message"));
        System.out.print( relationship.getProperty( "message" ) );
        System.out.print( secondNode.getProperty( "message" ) );


        System.out.print( firstNode.getProperty( "message" ) );
       //System.out.print( relationship.getProperty( "message" ) );
        //System.out.print( thirdNode.getProperty( "message" ) );


        greeting = ( (String) firstNode.getProperty( "message" ) )
                   + ( (String) relationship.getProperty( "message" ) )
                   + ( (String) secondNode.getProperty( "message" ) )
                   + ( (String) thirdNode.getProperty( "message" ) );

        tx.success();
    }

}

private void clearDb()
{
    try
    {
        FileUtils.deleteRecursively( new File( DB_PATH ) );
    }
    catch ( IOException e )
    {
        throw new RuntimeException( e );
    }
}

void removeData()
{
    try ( Transaction tx = graphDb.beginTx() )
    {

        firstNode.getSingleRelationship( RelTypes.LIKES, Direction.OUTGOING ).delete();
        firstNode.delete();
        secondNode.delete();
        thirdNode.delete();

        tx.success();
    }
}

void shutDown()
{
    System.out.println();
    System.out.println( "Shutting down database ..." );

    graphDb.shutdown();

}


private static void registerShutdownHook( final GraphDatabaseService graphDb )
{

    Runtime.getRuntime().addShutdownHook( new Thread()
    {
        @Override
        public void run()
        {
            graphDb.shutdown();
        }
    } );
}

}

Answer 1

正如异常所示，您正在调用

firstNode.getSingleRelationship( RelTypes.KNOWS, Direction.OUTGOING ).delete();

当你有多个来自firstNode的KNOWS类型的传出关系时(第一个节点->第二个节点和第一个节点->第三个节点)

也许您想使用http://api.neo4j.org/2.0.1/org/neo4j/graphdb/Node.html#getRelationships(org.neo4j.graphdb.RelationshipType,%20org.neo4j.graphdb.Direction)相反

对于输出，您希望从第一个节点开始获取所有关系，以便能够获取每个关系的结束节点。