سلام، یه وب سرویس نوشتم که یه متد به صورت زیر داره:



ServiceDataClassesDataContext db = newServiceDataClassesDataContext();
 


return db.tblAssistants.SingleOrDefault(p => p.Username == Username && p.Password == Pass);

حالا وقتی این وب سرویس به صو رت زیر فراخوانی میکونم error میده


AriaService.Service1SoapClient srv = new AriaService.Service1SoapClient();

 AriaService.tblAssistant User= srv.GetByIDAndPass("ad", "1");


این هم error:


System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> System.InvalidOperationException: There was an error generating the XML document. ---> System.InvalidOperationException: A circular reference was detected while serializing an object of type AriaWebService.tblAssistant.


 


at System.Xml.Serialization.XmlSerializationWriter.Wr  iteStartElement(String name, String ns, Object o, Boolean writePrefixed, XmlSerializerNamespaces xmlns)
 


at Microsoft.Xml.Serialization.GeneratedAssembly.XmlS  erializationWriter1.Write11_tblAssistant(String n, String ns, tblAssistant o, Boolean isNullable, Boolean needType)

at Microsoft.Xml.Serialization.GeneratedAssembly.XmlS  erializationWriter1.Write2_tblWihdrawal(String n, String ns, tblWihdrawal o, Boolean isNullable, Boolean needType)

at Microsoft.Xml.Serialization.GeneratedAssembly.XmlS  erializationWriter1.Write11_tblAssistant(String n, String ns, tblAssistant o, Boolean isNullable, Boolean needType)

at Microsoft.Xml.Serialization.GeneratedAssembly.XmlS  erializationWriter1.Write12_GetByIDAndPassResponse  (Object[] p)

at Microsoft.Xml.Serialization.GeneratedAssembly.Arra  yOfObjectSerializer1.Serialize(Object objectToSerialize, XmlSerializationWriter writer)

at System.Xml.Serialization.XmlSerializer.Serialize(X  mlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)

--- End of inner exception stack trace ---

at System.Xml.Serialization.XmlSerializer.Serialize(X  mlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)

at System.Xml.Serialization.XmlSerializer.Serialize(X  mlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle)

at System.Web.Services.Protocols.SoapServerProtocol.W  riteReturns(Object[] returnValues, Stream outputStream)

at System.Web.Services.Protocols.WebServiceHandler.Wr  iteReturns(Object[] returnValues)

at System.Web.Services.Protocols.WebServiceHandler.In  voke()
 


--- End of inner exception stack trace ---


 


خود وب سرویس کار میکونه تستش کردم ولی وقتی با linq میخوام اطلاعات بخونم این error میده. سرچ هم کردم ولی به جوابی نرسیدم