Question

我通过嵌入式Java API试验Neo4J。我的构建路径似乎没问题（运行时没有异常）。当我创建一些节点和关系时，我可以在它成功之后直接查询它。但是在关闭并重新运行我的程序之后，我只获取了我在新运行时创建的数据，而不是之前的数据。但是，如果我查看我的目录，我看到，每个运行时的大小都在增长，我执行数据创建。

这是我的代码：

public static void main(String[] args)
{
    GraphDatabaseService gdb = new GraphDatabaseFactory().newEmbeddedDatabase( "/mytestdb/" );

    create( gdb );
    query( gdb );

    gdb.shutdown();
}

private static void query( GraphDatabaseService gdb )
{
    StringLogger sl = StringLogger.wrap( new Writer()
    {

        @Override
        public void write( char[] arg0, int arg1, int arg2 ) throws IOException
        {
            for( int i=arg1; i<=arg2; i++ ) System.out.print( arg0[i] );

        }

        @Override
        public void flush() throws IOException
        {}

        @Override
        public void close() throws IOException
        {}
    } );
    ExecutionEngine ee = new ExecutionEngine( gdb, sl );
    ExecutionResult result = ee.execute( "MATCH (p:Privilleg) RETURN p" );
    System.out.println( result.dumpToString() );
}

private static void create( GraphDatabaseService gdb )
{
    Transaction tx = gdb.beginTx(); 
    Node project = gdb.createNode( MyLabels.Project );
    Node user = gdb.createNode( MyLabels.User );
    Node priv1 = gdb.createNode( MyLabels.Privilleg );
    Node priv2 = gdb.createNode( MyLabels.Privilleg );

    user.setProperty( "name", "Heinz" );
    user.setProperty( "email", "heinz@gmx.net" );
    priv1.setProperty( "name", "Allowed to read all" );
    priv1.setProperty( "targets", Short.MAX_VALUE );
    priv1.setProperty( "read", true );
    priv1.setProperty( "write", false );
    priv2.setProperty( "name", "Allowed to write all" );
    priv2.setProperty( "targets", Short.MAX_VALUE );
    priv2.setProperty( "read", false );
    priv2.setProperty( "write", true );
    project.setProperty( "name", "My first project" );
    project.setProperty( "sname", "STARTUP" );
    user.createRelationshipTo( priv1, MyRelationships.UserPrivilleg );
    user.createRelationshipTo( priv2, MyRelationships.UserPrivilleg );
    priv1.createRelationshipTo( project, MyRelationships.ProjectPrivilleg );
    priv2.createRelationshipTo( project, MyRelationships.ProjectPrivilleg );
    tx.success();
}

Answer 1

您的代码不会关闭交易。通常，您使用try-with-resources块：

try (Transaction tx=gdb.beginTx()) {
    // do stuff in the graph
    tx.success();
}

由于Transaction为AutoClosable，因此在离开代码块时将隐式调用其close()方法。如果（出于任何原因）您决定不使用try-with-resources，请务必明确调用close()。

另有说明：您的代码使用ExecutionEngine。自Neo4j 2.2起，您可以直接拨打gdb.execute(myCypherString)。

Answer 2

谢谢！这有效。此外，在我关闭事务之前，大约需要20秒才能将数据库缩小。现在这还不到一秒钟。

Neo4j仅在一个运行时内嵌入存储

2 个答案: