[英]Strange null reference exception in LINQ query with EF
我有以下三个相关的实体类:
public class ContextInstance
{
public Int64 Id { get; set; }
public virtual List<ContextParamValue> ContextParamValues { get; set; }
}
public class ContextParamValue
{
public Int64 Id { get; set; }
public virtual Int64 ContextParamId { get; set; }
public virtual ContextParam ContextParam { get; set; }
public virtual ContextInstance ContextInstance { get; set; }
public virtual Int64 ContextInstanceId { get; set; }
public string Value { get; set; }
}
public class ContextParam
{
public Int64 Id { get; set; }
[Required]
public string Name { get; set; }
[DefaultValue("")]
public string Description { get; set; }
}
我建立了流畅的关系如下:
modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
modelBuilder.Entity<ContextInstance>()
.HasMany(ci => ci.ContextParamValues)
.WithRequired(cpv => cpv.ContextInstance)
.HasForeignKey(cpv => cpv.ContextInstanceId)
.WillCascadeOnDelete(true);
我有以下“Helper”类,其ParamValueToList方法间歇性地抛出空引用异常 :
public class RuntimeHelper : IDisposable
{
DocumentDbContext db;
ConfigurationHelper ch;
private RuntimeHelper()
{
}
public RuntimeHelper(DocumentDbContext context)
{
db = context;
ch = new ConfigurationHelper(context);
}
public List<ContextParamValue> ParamValuesToList(string[] ParamNames, string[] ParamValues)
{
Trace.TraceInformation("-- ParamValuesToList invoked --");
if (ParamNames != null && ParamNames.Length != ParamValues.Length)
throw new System.ArgumentException("ParamNames and ParamValues may not differ in length.");
Dictionary<string, string> d = new Dictionary<string, string>();
for (int i = 0; i < ParamNames.Length; i++)
{
string pName = ParamNames[i];
string pValue = ParamValues[i];
d.Add(pName, pValue);
Trace.TraceInformation("ParamValuesToList Key: " + pName + "; Value: " + pValue + ";");
}
Trace.TraceInformation("Value of db:" + db.ContextParamValues.ToString());
var cpvList = db.ContextParamValues
.Include(x => x.ContextParam)
.ToArray<ContextParamValue>();
List<ContextParamValue> lst = cpvList
.Where(pv => d.Contains(new KeyValuePair<string, string>(pv.ContextParam.Name, pv.Value)))
//.Where(pv => true == true)
.ToList<ContextParamValue>();
Trace.TraceInformation("-- ParamValuesToList executed --");
return lst;
}
public List<ContextInstance> GetContextInstances(List<ContextParamValue> ContextParamValues, bool AsNoTracking = false)
{
if (!AsNoTracking)
return db.ContextInstances
.Include(x => x.ContextClass)
.Include(x => x.ContextParamValues.Select(p => p.ContextParam))
.Include(x => x.Documents)
.AsEnumerable<ContextInstance>() // <-- Allows boolean method as part of LINQ query
.Where(ci => IsSubset(ci.ContextParamValues, ContextParamValues))
.ToList<ContextInstance>();
else
return db.ContextInstances
.Include(x => x.ContextClass)
.Include(x => x.ContextParamValues.Select(p => p.ContextParam))
.Include(x => x.Documents)
.AsNoTracking()
.AsEnumerable<ContextInstance>()// <-- Allows boolean method as part of LINQ query
.Where(ci => IsSubset(ci.ContextParamValues, ContextParamValues))
.ToList<ContextInstance>();
}
public List<ContextInstance> GetContextInstances(string[] ParamNames, string[] ParamValues, bool AsNoTracking = false)
{
return GetContextInstances(ParamValuesToList(ParamNames, ParamValues), AsNoTracking);
}
}
上面抛出错误的方法的具体说法是
List<ContextParamValue> lst = cpvList
.Where(pv => d.Contains(new KeyValuePair<string, string>(pv.ContextParam.Name, pv.Value)))
.ToList<ContextParamValue>();
在以下条件下不引发空引用异常:
空引用异常在以下条件下抛出:
我可以确认以下关于有问题的帮助方法:
运行时期间会生成以下跟踪和堆栈 跟踪信息:
应用程序:2014-05-16T19:00:20 PID [4800]错误System.NullReferenceException:对象引用未设置为对象的实例。 应用程序:在DocumentManagement.Helpers.RuntimeHelper。<> c__DisplayClass28.b__27(ContextParamValue pv)中的c:\\ Users \\ xxx \\ Dropbox \\ xxx \\ Active Projects \\ xxx \\ DocumentManagement \\ Helpers \\ DocsHelper_RT.cs:第229行应用程序:at System。 Linq.Enumerable.WhereArrayIterator1.MoveNext()Application:at System.Collections.Generic.List1..ctor(IEnumerable1 collection)Application:at System.Linq.Enumerable.ToList [TSource](IEnumerable1 source)Application:at DocumentManagement.Helpers。 RuntimeHelper.ParamValuesToList(String [] ParamNames,String [] ParamValues)在c:\\ Users \\ xxx \\ Dropbox \\ xxx \\ Active Projects \\ xxx \\ DocumentManagement \\ Helpers \\ DocsHelper_RT.cs:第228行应用程序:在DocumentManagement.Helpers.RuntimeHelper。 GetContextInstances(String [] ParamNames,String [] ParamValues,Boolean AsNoTracking)在c:\\ Users \\ xxx \\ Dropbox \\ xxx \\ Active Projects \\ xxx \\ DocumentManagement \\ Helpers \\ DocsHelper_RT.cs:第262行应用程序:at xxx.Controllers.ClientController c:\\ Users \\ xxx \\ D中的.LoadStep2(Int64 ClientId,String Error) ropbox \\ xxx \\ Active Projects \\ xxx \\ xxx \\ Views \\ Client \\ ClientController.cs:第198行
如果pv.ContextParam为null,则代码抛出异常的唯一方法是,因为这是您解除引用可能导致空指针异常的内容的唯一位置。
如果您具有ContextParamValues记录而没有相应的ContextParam记录,则会发生这种情况,因此ContextParam将为null。 由于我们无法看到您的数据模型,因此您必须检查它。
添加这行代码并检查调试器以查看它是否为真:
bool containsNulls = db.ContextParamValues
.Include(x => x.ContextParam)
.Any(x => x.ContextParam == null)
编辑(删除所有中间步骤,如果您感兴趣,请查看历史记录):
嗯,这实际上并没有回答这个问题,但它可以解决你的问题。 让我们重写您的代码,使其更简单,更高效。 如果我正确地阅读了您的代码,那么您要做的就是返回与所提供的名称/值对相关联的ContextInstances,正确吗?
为什么不这样做(根据需要添加包括):
public List<ContextInstance> GetContextInstances(
string[] ParamNames, string[] ParamValues, bool AsNoTracking = false)
{
var p = ParamNames.Zip(ParamValues, (a,b) => a+b);
var ctx = db.ContextInstances
.Where(x => p.All(y => x.ContextParamValues
.Select(z => z.ContextParam.Name + z.Value).Contains(y)));
return (AsNoTracking ? ctx.AsNoTracking() : ctx).ToList();
}
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.