Question

我想使用cypher查询在java中获取特定节点但我无法获取它。并且在debbuging时间debbuger从fetchNodes（）方法中的特定for循环返回。我无法正确地解读它。

类：NewCypherQuery（bean）

public class NewCypherQuery {
private static final String DB_PATH = "/var/lib/neo4j/data/";
private static String resultString, columnsString, nodeResult, rows = "",
        query;
private static ExecutionResult result;
private static ExecutionEngine engine;
private static GraphDatabaseService db;
private static Node amad = null,pari=null,sona=null;
private static Relationship rel;

public static void callAllMethods() {
    clearDbPath();
    setUp();
    createNodes();
    // fetchNodes();
    matchData();

}

private static void setUp() {
    db = new GraphDatabaseFactory().newEmbeddedDatabase(DB_PATH);
    engine = new ExecutionEngine(db);

}

private static void createNodes() {
    try (Transaction tx = db.beginTx();) {

        amad = db.createNode();
        amad.setProperty("name", "Amad");
        amad.setProperty("age", 24);
        amad.setProperty("edu", "mscit");

        pari = db.createNode();
        pari.setProperty("name", "Pari");
        pari.setProperty("age", 20);
        pari.setProperty("edu", "mscit");

        sona = db.createNode();
        sona.setProperty("name", "Sona");
        sona.setProperty("age", 21);
        sona.setProperty("edu", "mscit");

        rel=amad.createRelationshipTo(pari, RelTypes.KNOWS);
        rel.setProperty("rel", "friend");
        rel=pari.createRelationshipTo(sona, RelTypes.KNOWS);
        rel.setProperty("rel", "friend");

        /*query = "CREATE (amad:User1 { name: 'Amad1',age : 20,education : 'Mscit' }),(pari:User1 { name : 'Pari1' }),(sona:User1 { name : 'Sona1'}),(amad)-[:FRIEND]->(pari),(pari)-[:FRIEND]->(sona)";
        result = engine.execute(query);*/
        System.out.println("Nodes created.....");
        tx.success();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

private static void fetchNodes() {
    try (Transaction ignored = db.beginTx();) {
        result = engine
                .execute("start n=node(*) where n.name = 'Rita' return n, n.name");
        // END SNIPPET: execute
        // START SNIPPET: items
        Iterator<Node> n_column = result.columnAs("n");

        for (Node node : IteratorUtil.asIterable(n_column)) {
            // note: we're grabbing the name property from the node,
            // not from the n.name in this case.
            nodeResult = node + ": " + node.getProperty("name");
            System.out.println(nodeResult.length());
        }

        List<String> columns = result.columns();
        // END SNIPPET: columns
        // the result is now empty, get a new one
        result = engine
                .execute("start n=node(*) where n.name = 'Rita' return n, n.name");
        // START SNIPPET: rows
        for (Map<String, Object> row : result) {
            for (Entry<String, Object> column : row.entrySet()) {
                rows += column.getKey() + ": " + column.getValue() + "; ";
            }
            rows += "\n";

            // END SNIPPET: rows
            resultString = engine
                    .execute(
                            "start n=node(*) where n.name = 'Rita' return n, n.name")
                    .dumpToString();
            System.out.println(resultString);
            columnsString = columns.toString();
            db.shutdown();
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
}

private static void clearDbPath() {
    try {
        deleteRecursively(new File(DB_PATH));
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}
}

servlet：（InsertNodes）

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws   ServletException, IOException {
    // TODO Auto-generated method stub

    NewCypherQuery ncq=new NewCypherQuery();
    ncq.callAllMethods();
}

的index.jsp

<form method="post" action="InsertNodes">
<input type="text" name="txtname" value="Hello World !!!!!"></input>
<input type="submit" value="Neo4j World"></input> 
</form>

Answer 1

我绝对不确定我是否理解你的问题。

您只能在ExecutionResult上进行一次迭代。由于迭代器已经用完，后续迭代将不执行任何操作。这可能看起来很奇怪。当您想要在使用它之前记录查询结果时。内部Cypher尽可能保持内存保守，并试图避免在使用迭代器时构建有利于直接遍历图形的集合。

如果您想多次迭代，您需要填充一个集合，您可以使用例如IteratorUtil.asList。这样做的结果就是能够以内存消耗为代价进行多次迭代。

Answer 2

Chauhan保持，

你不应该得到任何结果。您创建了三个节点，名称为Amad，Pari和Sona。然后，您搜索名为Rita的节点。没有名为Rita的节点。您的编码也存在许多其他问题，但Neo4j正在按照您的要求进行操作。

恩典与和平，

吉姆

我想使用cypher查询在java中获取特定节点但我无法获取它

2 个答案: