使用Java API的Neo4j Cypher查询1.9.6问题
我正在使用以下查询使用Java API的Neo4j Cypher查询1.9.6问题,java,neo4j,cypher,Java,Neo4j,Cypher,我正在使用以下查询 START n=node(*) MATCH(n) WHERE n.Gender ?="Female" RETURN n 它在服务器上运行得非常好 我的程序如下 void query() { ExecutionResult result,; Transaction tx=null; ExecutionEngine engine = new ExecutionEngine( grap
START n=node(*)
MATCH(n)
WHERE n.Gender ?="Female"
RETURN n
它在服务器上运行得非常好
我的程序如下
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();
}
}
当我试图通过程序执行它时,它进入catch块并打印以下stacktrace
[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)]
我认为我以错误的方式传递了参数“female”。我应该首先说我不熟悉Neo4j的Java API。但从我所看到的: 用密码
MATCH (n)
这是不正确的。您需要描述完整的路径,例如MATCH(n)-->(m)
或MATCH(n)-[:friend\u of]-(m)
,或者一起跳过MATCH子句。在您的特定示例中,您不需要match子句,因此可以跳过它
第二件事是-是的,您没有正确地传递参数-您可以在这里看到一些关于如何将参数传递给ExecutionRegine的示例:
在您的示例中,您可以执行以下操作:
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();
}
}
void查询(){
执行结果,;
事务tx=null;
ExecutionEngine=新的ExecutionEngine(graphDb);
尝试
{
Map params=新的HashMap();
params.put(“性别”、“女性”);
tx=graphDb.beginTx();
结果=engine.execute(“启动n=节点(*),其中n.Gender?={Gender}返回n”,参数);
System.out.println(result.dumpToString());
成功();
}
捕获(例外e)
{
尝试
{
文件f=新文件(“trace.txt”);
BufferedWriter br=新的BufferedWriter(新文件写入程序(f,true));
tx.故障();
k=Arrays.toString(例如getStackTrace());
系统输出println(k);
br.写(k);
br.close();
抛出新IOException();
}
捕获(例外情况除外)
{
}
}
最后
{
tx.finish();
}
}
P.S.如果您的查询根本没有改变,您也可以这样编写:engine.execute(“start n=node(*)where n.Gender?=“Female”return n”)
并完全跳过映射。您忘记将参数映射添加到执行调用。通常情况下,您只会对真正固定的值(即常量)使用文本。您的异常处理块很奇怪。只需使用日志框架(或java.util.logging)将错误消息记录到磁盘。您忘记将参数映射传递给cypher的执行方法,execute(query,params)