使用Java API的Neo4j Cypher Query 1.9.6问题

Question

我使用以下查询

     START n=node(*)
     MATCH(n)
     WHERE n.Gender ?="Female"
     RETURN n

它在服务器中完美运行。

我的计划如下

    void query()
      {
      ExecutionResult result,;
       Transaction tx=null;
     ExecutionEngine engine = new ExecutionEngine( graphDb );

    try
    {
        String name="Female";
        tx=graphDb.beginTx();
     result=engine.execute("start n=node(*)match(n)where n.Gender ?={Female} return n");
       System.out.println(result.dumpToString());
       tx.success();
    }

    catch(Exception e)
    {
        try
        {           
            File f=new File("trace.txt");
            BufferedWriter br=new BufferedWriter(new FileWriter(f,true));
            tx.failure();
            k=Arrays.toString(e.getStackTrace());
            System.out.println(k);
            br.write(k);
            br.close();
            throw new IOException();
        }
        catch (Exception ex)
        {
        }
      }
    finally
    {
        tx.finish();
    }

}

当我尝试通过程序执行它时，它进入catch块并打印下面的堆栈跟踪

            [org.neo4j.cypher.internal.pipes.QueryState$$anonfun$getParam$1.apply(QueryState.scala:60),
             org.neo4j.cypher.internal.pipes.QueryState$$anonfun$getParam$1.apply(QueryState.scala:60),
             scala.collection.MapLike$class.getOrElse(MapLike.scala:128), 
             scala.collection.AbstractMap.getOrElse(Map.scala:58), 
             org.neo4j.cypher.internal.pipes.QueryState.getParam(QueryState.scala:60), 
             org.neo4j.cypher.internal.commands.expressions.ParameterExpression.apply(ParameterExpression.scala:27), 
             org.neo4j.cypher.internal.commands.Equals.isMatch(ComparablePredicate.scala:59),
             org.neo4j.cypher.internal.commands.NullablePredicate.isMatch(Predicate.scala:59),
             org.neo4j.cypher.internal.pipes.FilterPipe$$anonfun$internalCreateResults$1.apply(FilterPipe.scala:30), 
             org.neo4j.cypher.internal.pipes.FilterPipe$$anonfun$internalCreateResults$1.apply(FilterPipe.scala:30),
             scala.collection.Iterator$$anon$14.hasNext(Iterator.scala:390), 
             org.neo4j.cypher.internal.ClosingIterator$$anonfun$next$1.apply(ClosingIterator.scala:45), 
             org.neo4j.cypher.internal.ClosingIterator.failIfThrows(ClosingIterator.scala:86),
             org.neo4j.cypher.internal.ClosingIterator.next(ClosingIterator.scala:43),
             scala.collection.Iterator$class.foreach(Iterator.scala:727), 
             org.neo4j.cypher.internal.ClosingIterator.foreach(ClosingIterator.scala:31),
             scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:48), 
             scala.collection.mutable.ListBuffer.$plus$plus$eq(ListBuffer.scala:178),
             scala.collection.mutable.ListBuffer.$plus$plus$eq(ListBuffer.scala:45), 
             scala.collection.TraversableOnce$class.to(TraversableOnce.scala:259),
             org.neo4j.cypher.internal.ClosingIterator.to(ClosingIterator.scala:31),
             scala.collection.TraversableOnce$class.toList(TraversableOnce.scala:243), 
             org.neo4j.cypher.internal.ClosingIterator.toList(ClosingIterator.scala:31),
             org.neo4j.cypher.PipeExecutionResult.eagerResult(PipeExecutionResult.scala:100),
             org.neo4j.cypher.PipeExecutionResult.dumpToString(PipeExecutionResult.scala:103),
             org.neo4j.cypher.PipeExecutionResult.dumpToString$lzycompute(PipeExecutionResult.scala:143), 
             org.neo4j.cypher.PipeExecutionResult.dumpToString(PipeExecutionResult.scala:140),
             org.neo4j.cypher.javacompat.ExecutionResult.dumpToString(ExecutionResult.java:102),
             Neo4jQuery.query(Neo4jQuery.java:90), Neo4jQuery.main(Neo4jQuery.java:35),
             __SHELL3.run(__SHELL3.java:6), sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method), 
             sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57), 
             sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43), 
             java.lang.reflect.Method.invoke(Method.java:606), bluej.runtime.ExecServer$3.run(ExecServer.java:725)]

我想我以错误的方式传递参数“女性”。

Answer 1

我应该首先说我不熟悉Neo4j的Java API。 但从我所看到的：

在Cypher

MATCH (n)

是不正确的。 你需要描述一个完整的路径，比如MATCH (n)-->(m)或MATCH (n)-[:friend_of]-(m) ，或者一起跳过匹配子句。 在您的特定示例中，您不需要match子句，因此您可以跳过它。

第二件事是 - 是的，你没有正确地传递参数 - 你可以看到一些关于如何将参数传递给ExecutionEgine的例子： http ： //docs.neo4j.org/chunked/stable/tutorials-cypher-parameters- java.html

在您的示例中，您可以：

void query() {
    ExecutionResult result,;
    Transaction tx=null;
    ExecutionEngine engine = new ExecutionEngine( graphDb );

    try
    {
        Map<String, Object> params = new HashMap<String, Object>();
        params.put("gender", "Female");
        tx=graphDb.beginTx();
        result = engine.execute("start n=node(*) where n.Gender ?= {gender} return n",params);
        System.out.println(result.dumpToString());
        tx.success();
    }
    catch(Exception e)
    {
        try
        {           
            File f=new File("trace.txt");
            BufferedWriter br=new BufferedWriter(new FileWriter(f,true));
            tx.failure();
            k=Arrays.toString(e.getStackTrace());
            System.out.println(k);
            br.write(k);
            br.close();
            throw new IOException();
        }
        catch (Exception ex)
        {
        }
      }
    finally
    {
        tx.finish();
    }

}