5
我尝试做以下...的LINQ to SQL - 指定的转换是无效的 - 的SingleOrDefault（）
Request request = (
from r in db.Requests
where r.Status == "Processing" && r.Locked == false
select r
).SingleOrDefault();
它抛出以下异常...
Message:
Specified cast is not valid.
StackTrace:
at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source)
at GDRequestProcessor.Worker.GetNextRequest()
任何人都可以帮助我吗？ 在此先感谢！
模式的详细信息可以在下面找到...
[Table(Name="dbo.Requests")]
public partial class Request : INotifyPropertyChanging, INotifyPropertyChanged
{
private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
private int _RequestId;
private string _LoanNumber;
private string _ClientCode;
private int _RequestTypeId;
private bool _HasParameters;
private string _Status;
private bool _Locked;
private string _ErrorMessage;
private int _ReferenceId;
private EntitySet<RequestParameter> _RequestParameters;
private EntityRef<RequestType> _RequestType;
#region Extensibility Method Definitions
partial void OnLoaded();
partial void OnValidate(System.Data.Linq.ChangeAction action);
partial void OnCreated();
partial void OnRequestIdChanging(int value);
partial void OnRequestIdChanged();
partial void OnLoanNumberChanging(string value);
partial void OnLoanNumberChanged();
partial void OnClientCodeChanging(string value);
partial void OnClientCodeChanged();
partial void OnRequestTypeIdChanging(int value);
partial void OnRequestTypeIdChanged();
partial void OnHasParametersChanging(bool value);
partial void OnHasParametersChanged();
partial void OnStatusChanging(string value);
partial void OnStatusChanged();
partial void OnLockedChanging(bool value);
partial void OnLockedChanged();
partial void OnErrorMessageChanging(string value);
partial void OnErrorMessageChanged();
partial void OnReferenceIdChanging(int value);
partial void OnReferenceIdChanged();
#endregion
public Request()
{
this._RequestParameters = new EntitySet<RequestParameter>(new Action<RequestParameter>(this.attach_RequestParameters), new Action<RequestParameter>(this.detach_RequestParameters));
this._RequestType = default(EntityRef<RequestType>);
OnCreated();
}
[Column(Storage="_RequestId", AutoSync=AutoSync.OnInsert, DbType="Int NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
public int RequestId
{
get
{
return this._RequestId;
}
set
{
if ((this._RequestId != value))
{
this.OnRequestIdChanging(value);
this.SendPropertyChanging();
this._RequestId = value;
this.SendPropertyChanged("RequestId");
this.OnRequestIdChanged();
}
}
}
[Column(Storage="_LoanNumber", DbType="VarChar(50) NOT NULL", CanBeNull=false)]
public string LoanNumber
{
get
{
return this._LoanNumber;
}
set
{
if ((this._LoanNumber != value))
{
this.OnLoanNumberChanging(value);
this.SendPropertyChanging();
this._LoanNumber = value;
this.SendPropertyChanged("LoanNumber");
this.OnLoanNumberChanged();
}
}
}
[Column(Storage="_ClientCode", DbType="VarChar(50) NOT NULL", CanBeNull=false)]
public string ClientCode
{
get
{
return this._ClientCode;
}
set
{
if ((this._ClientCode != value))
{
this.OnClientCodeChanging(value);
this.SendPropertyChanging();
this._ClientCode = value;
this.SendPropertyChanged("ClientCode");
this.OnClientCodeChanged();
}
}
}
[Column(Storage="_RequestTypeId", DbType="Int NOT NULL")]
public int RequestTypeId
{
get
{
return this._RequestTypeId;
}
set
{
if ((this._RequestTypeId != value))
{
if (this._RequestType.HasLoadedOrAssignedValue)
{
throw new System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException();
}
this.OnRequestTypeIdChanging(value);
this.SendPropertyChanging();
this._RequestTypeId = value;
this.SendPropertyChanged("RequestTypeId");
this.OnRequestTypeIdChanged();
}
}
}
[Column(Storage="_HasParameters", DbType="Bit NOT NULL")]
public bool HasParameters
{
get
{
return this._HasParameters;
}
set
{
if ((this._HasParameters != value))
{
this.OnHasParametersChanging(value);
this.SendPropertyChanging();
this._HasParameters = value;
this.SendPropertyChanged("HasParameters");
this.OnHasParametersChanged();
}
}
}
[Column(Storage="_Status", DbType="VarChar(50) NOT NULL", CanBeNull=false)]
public string Status
{
get
{
return this._Status;
}
set
{
if ((this._Status != value))
{
this.OnStatusChanging(value);
this.SendPropertyChanging();
this._Status = value;
this.SendPropertyChanged("Status");
this.OnStatusChanged();
}
}
}
[Column(Storage="_Locked", DbType="Bit NOT NULL")]
public bool Locked
{
get
{
return this._Locked;
}
set
{
if ((this._Locked != value))
{
this.OnLockedChanging(value);
this.SendPropertyChanging();
this._Locked = value;
this.SendPropertyChanged("Locked");
this.OnLockedChanged();
}
}
}
[Column(Storage="_ErrorMessage", DbType="VarChar(255)")]
public string ErrorMessage
{
get
{
return this._ErrorMessage;
}
set
{
if ((this._ErrorMessage != value))
{
this.OnErrorMessageChanging(value);
this.SendPropertyChanging();
this._ErrorMessage = value;
this.SendPropertyChanged("ErrorMessage");
this.OnErrorMessageChanged();
}
}
}
[Column(Storage="_ReferenceId", DbType="Int NOT NULL")]
public int ReferenceId
{
get
{
return this._ReferenceId;
}
set
{
if ((this._ReferenceId != value))
{
this.OnReferenceIdChanging(value);
this.SendPropertyChanging();
this._ReferenceId = value;
this.SendPropertyChanged("ReferenceId");
this.OnReferenceIdChanged();
}
}
}
这通常发生在C＃对象上的一个或多个属性的类型与列的类型不匹配时。你能发布Request表的模式和Request类的属性类型吗？ – 2010-03-12 22:12:22
请求类型是什么？如果你使用var请求怎么办？ SingleOrDefault的返回类型是什么？ – 2010-03-12 21:56:14
请求反映在数据库表中的记录请求... 我试着用下面的代码和stil得到错误... var query =（from r in db.Requests where r.Status.Equals（“Processing” ）&& r.Locked.Equals（false）select r）.SingleOrDefault（）; SingleOrDefault的返回类型是请求 – NullReference 2010-03-12 22:04:08