本文介绍了GraphEngine LIKQ查询引发System.NullReferenceException的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我开始使用并尝试构建一个LIKQ示例，我的代码如下：
I started to use Microsoft GraphEngine and try to build a LIKQ example, my code below:
TSL代码：
cell People
{
[Index]
string Name;
optional int Age;
[GraphEdge]
optional List<CellId> Friends;
}
主程序：
using System;
using System.Collections.Generic;
using System.Linq;
using FanoutSearch;
using FanoutSearch.LIKQ;
using PeopleModel;
using Trinity;
using Trinity.Network;
using Action = FanoutSearch.Action;
namespace People_LIKQ
{
class Program
{
static void Main(string[] args)
{
//GenerateData();
LikqQurety();
}
/// <summary>
/// Try to query with LIKQ
/// </summary>
static void LikqQurety()
{
TrinityServer server=new TrinityServer();
server.RegisterCommunicationModule<FanoutSearchModule>();
server.Start();
Global.LocalStorage.LoadStorage();
var startNodes = from node in Global.LocalStorage.People_Selector()
where node.Name == "张三"
select node;
var startNode = startNodes.FirstOrDefault();
//System.NullReferenceException here
var datas=KnowledgeGraph.StartFrom(startNode)
.FollowEdge("Friends").VisitNode(_=>Action.Continue)
.FollowEdge("Friends").VisitNode(_=>Action.Continue)
.FollowEdge("Friends").VisitNode(_=>Action.Return).ToList();
foreach (PathDescriptor path in datas)
{
var ids = path.Select(ToReachableIDs).ToList();
}
}
private static object ToReachableIDs(NodeDescriptor arg)
{
using (var cell=Global.LocalStorage.UsePeople(arg.id))
{
Console.WriteLine(cell.Name);
return cell.CellID.Value;
}
}
/// <summary>
/// Generate somet testing data
/// </summary>
static void GenerateData()
{
Console.WriteLine("开始生成测试数据");
People zhangsan=new People(Name:"张三",Age:34,Friends:new List<long>());
People lisi=new People(Name:"李四",Age:33,Friends:new List<long>());
People wangwu=new People(Name:"王五",Age:26,Friends:new List<long>());
People xiaoming=new People(Name:"小明",Age:15,Friends:new List<long>());
People xiaohua=new People(Name:"小花",Age:16,Friends:new List<long>());
People jack=new People(Name:"Jack",Age:30,Friends:new List<long>());
People rose=new People(Name:"Rose",Age:20,Friends:new List<long>());
zhangsan.Friends.AddRange(new []{lisi.CellID,wangwu.CellID});
lisi.Friends.AddRange(new []{zhangsan.CellID,xiaoming.CellID,jack.CellID});
wangwu.Friends.AddRange(new []{zhangsan.CellID,xiaoming.CellID,jack.CellID});
xiaoming.Friends.AddRange(new []{lisi.CellID,xiaohua.CellID,wangwu.CellID});
xiaohua.Friends.AddRange(new []{xiaoming.CellID,rose.CellID});
jack.Friends.AddRange(new []{lisi.CellID,wangwu.CellID,rose.CellID});
rose.Friends.AddRange(new []{jack.CellID,xiaohua.CellID});
Global.LocalStorage.SavePeople(zhangsan);
Global.LocalStorage.SavePeople(lisi);
Global.LocalStorage.SavePeople(wangwu);
Global.LocalStorage.SavePeople(xiaoming);
Global.LocalStorage.SavePeople(xiaohua);
Global.LocalStorage.SavePeople(jack);
Global.LocalStorage.SavePeople(rose);
Global.LocalStorage.SaveStorage();
Console.WriteLine("数据生成并保存成功");
}
}
}
当我生成测试数据并尝试运行LIKQ查询时，它将引发以下异常：
When I generated the testing data and try to run LIKQ query, It throws the exception below:
Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
at FanoutSearch.ExpressionSerializer.EnsureSerializer()
at FanoutSearch.ExpressionSerializer.Serialize(Expression pred)
at FanoutSearch.FanoutSearchDescriptor.<>c. <Serialize>b__22_0(Expression pred)
at System.Linq.Enumerable.SelectListIterator`2.ToList()
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at FanoutSearch.FanoutSearchDescriptor.Serialize()
at FanoutSearch.FanoutSearchDescriptor._ExecuteQuery()
at FanoutSearch.FanoutSearchDescriptor.GetEnumerator()
at System.Collections.Generic.List`1.AddEnumerable(IEnumerable`1 enumerable)
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at People_LIKQ.Program.LikqQurety() in /home/coder/Documents/NetCore/LIKQ-Examples/People-LIKQ/Program.cs:line 32
at People_LIKQ.Program.Main(String[] args) in /home/coder/Documents/NetCore/LIKQ-Examples/People-LIKQ/Program.cs:line 18
测试da tabase似乎是一个很好的例子，但是关于它的文档并不多，而且我无法正确设置它，构建成功，但会出现相同的错误。
The freebase-likq example test database seems to be a good example, but there is not much documents about it, and I can't set it up correctly, I build it successfully,but run with the same error.
我的测试环境是：
Ubuntu16.04 x64
.NetCore 2.1.4
GraphEngine.Core 1.0.9083 (I build it myself,The NuGet package outdated.)
GraphEngine.LIKQ 1.0.9083
推荐答案
我自己弄清楚，原因是这里显示了一个实现IExpressionSerializer接口的ExpressionSerializer寄存器，下面是我的示例：
I figure out with myself, the reason is there show register a ExpressionSerializer which implement the IExpressionSerializer interface, my example below:
public class ExpressionSerializer:IExpressionSerializer
{
private static XmlSerializer m_serializer = null;
private static NodeFactory m_factory = null;
public ExpressionSerializer()
{
m_serializer=new XmlSerializer();
m_serializer.AddKnownType(typeof(FanoutSearch.Action));
m_factory=new NodeFactory();
}
public string Serialize(Expression pred)
{
return pred.ToXml(m_factory,m_serializer);
}
public Func<ICellAccessor, Action> DeserializeTraverseAction(string pred)
{
var func_exp = m_serializer.Deserialize<LambdaExpressionNode>(pred)
.ToExpression<Func<ICellAccessor, FanoutSearch.Action>>();
return func_exp.Compile();
}
public Func<ICellAccessor, bool> DeserializeOriginPredicate(string pred)
{
var fun_exp = m_serializer.Deserialize<LambdaExpressionNode>(pred)
.ToExpression<Func<ICellAccessor, bool>>();
return fun_exp.Compile();
}
}
并在Program.cs中注册：
And register in Program.cs:
Global.LocalStorage.LoadStorage();
TrinityConfig.HttpPort = 80;
FanoutSearchModule.EnableExternalQuery(true);
FanoutSearchModule.SetQueryTimeout(3000);
FanoutSearchModule.RegisterIndexService(Indexer);
FanoutSearchModule.RegisterExpressionSerializerFactory(()=>new ExpressionSerializer());
TrinityServer server=new TrinityServer();
server.RegisterCommunicationModule<FanoutSearchModule>();
server.Start();
这篇关于GraphEngine LIKQ查询引发System.NullReferenceException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！