我在asp.net中为我的数据库创建了四个模型类，ideia是为问卷调查创建模型，其中调查问卷有多个问题，每个问题都是多个答案，答案有3种类型，多个答案在哪里用户只能选择一个答案，多个答案，用户可以选择多个答案，并完成文本答案。一个问题只有答案类型。
我可以在数据库中插入数据但是当我对问题表或答案表进行GET（使用邮递员）时，我收到以下错误：
"Message": "An error has occurred.",
"ExceptionMessage": "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.",
"ExceptionType": "System.InvalidOperationException",
"StackTrace": null,
"InnerException": {
"Message": "An error has occurred.",
"ExceptionMessage": "Error getting value from 'Questionnaire' on 'System.Data.Entity.DynamicProxies.Question_A710DEFF3886CBDE62F28495FD980EB31736277C66BCA5CDB9DCFB9CD2A69007'.",
"ExceptionType": "Newtonsoft.Json.JsonSerializationException",
"StackTrace": " em Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)\r\n em Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)\r\n em Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n em Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n em Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n em Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n em Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n em Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n em System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n em System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n em System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)\r\n em System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\r\n--- Fim do rastreio da pilha da localização anterior em que a excepção foi emitida ---\r\n em System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n em System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n em System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()",
"InnerException": {
"Message": "An error has occurred.",
"ExceptionMessage": "An error occurred while executing the command definition. See the inner exception for details.",
"ExceptionType": "System.Data.Entity.Core.EntityCommandExecutionException",
"StackTrace": " em System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior)\r\n em System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlan.Execute[TResultType](ObjectContext context, ObjectParameterCollection parameterValues)\r\n em System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()\r\n em System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)\r\n em System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()\r\n em System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)\r\n em System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)\r\n em System.Data.Entity.Core.Objects.ObjectQuery`1.Execute(MergeOption mergeOption)\r\n em System.Data.Entity.Core.Objects.DataClasses.EntityReference`1.Load(MergeOption mergeOption)\r\n em System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.DeferredLoad()\r\n em System.Data.Entity.Core.Objects.Internal.LazyLoadBehavior.LoadProperty[TItem](TItem propertyValue, String relationshipName, String targetRoleName, Boolean mustBeNull, Object wrapperObject)\r\n em System.Data.Entity.Core.Objects.Internal.LazyLoadBehavior.<>c__DisplayClass7`2.<GetInterceptorDelegate>b__2(TProxy proxy, TItem item)\r\n em System.Data.Entity.DynamicProxies.Question_A710DEFF3886CBDE62F28495FD980EB31736277C66BCA5CDB9DCFB9CD2A69007.get_Inqueritov()\r\n em GetInqueritov(Object )\r\n em Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)",
"InnerException": {
"Message": "An error has occurred.",
"ExceptionMessage": "Já existe um DataReader aberto associado a este Command, que tem de ser fechado primeiro.",
"ExceptionType": "System.InvalidOperationException",
"StackTrace": " em System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command)\r\n em System.Data.SqlClient.SqlConnection.ValidateConnectionFor
表格
public class TypeAnswerv
{
public TypeAnswerv()
{
Questions=new HashSet<Question>();
}
[Key]
public int TypeAnswerId { get; set; }
[Required]
public string TypesAnswer { get; set; }
public ICollection<Question> Questions { get; set; }
}
public class Answer
{
[Key]
public int AnswerId { get; set; }
[Required]
public string Answerv { get; set; }
public virtual Question Question { get; set; }
}
public class Questionnaire
{
public Questionnaire()
{
Questions=new HashSet<Question>();
}
[Required]
[Key]
public int QuestionnaireId { get; set; }
[Required]
public string Name { get; set; }
public DateTime DateCreation { get; set; }
public DateTime ExpireDate { get; set; }
public int ExpireIn { get; set; }
public ICollection<Question> Questions { get; set; }
}
public class Question
{
public Question()
{
Answers=new HashSet<Answer>();
}
[Key]
public int QuestionId { get; set; }
public string Questionv { get; set; }
public ICollection<Answer> Answers { get; set; }
public virtual TypeAnswerv TypeAnswer { get; set; }
public virtual Questionnaire Questionnaire { get; set; }
}
控制器：
答案控制器：
public class AnswersController : ApiController
{
private QuestionarioContext db = new QuestionarioContext();
// GET: api/Answers
public IQueryable<Answer> GetAnswers()
{
return db.Answers;
}
// GET: api/Answers/5
[ResponseType(typeof(Answer))]
public async Task<IHttpActionResult> GetAnswer(int id)
{
Answer answer = await db.Answers.FindAsync(id);
if (answer == null)
{
return NotFound();
}
return Ok(answer);
}
// PUT: api/Answers/5
[ResponseType(typeof(void))]
public async Task<IHttpActionResult> PutAnswer(int id, Answer answer)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (id != answer.AnswerId)
{
return BadRequest();
}
db.Entry(answer).State = EntityState.Modified;
try
{
await db.SaveChangesAsync();
}
catch (DbUpdateConcurrencyException)
{
if (!AnswerExists(id))
{
return NotFound();
}
else
{
throw;
}
}
return StatusCode(HttpStatusCode.NoContent);
}
// POST: api/Answers
[ResponseType(typeof(Answer))]
public async Task<IHttpActionResult> PostAnswer(Answer answer)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
db.Answers.Add(answer);
await db.SaveChangesAsync();
return CreatedAtRoute("DefaultApi", new { id = answer.AnswerId }, answer);
}
// DELETE: api/Answers/5
[ResponseType(typeof(Answer))]
public async Task<IHttpActionResult> DeleteAnswer(int id)
{
Answer answer = await db.Answers.FindAsync(id);
if (answer == null)
{
return NotFound();
}
db.Answers.Remove(answer);
await db.SaveChangesAsync();
return Ok(answer);
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
db.Dispose();
}
base.Dispose(disposing);
}
private bool AnswerExists(int id)
{
return db.Answers.Count(e => e.AnswerId == id) > 0;
}
}
问题控制员：
public class QuestionsController : ApiController
{
private QuestionarioContext db = new QuestionarioContext();
// GET: api/Questions
public IQueryable<Question> GetQuestions()
{
return db.Questions;
}
// GET: api/Questions/5
[ResponseType(typeof(Question))]
public async Task<IHttpActionResult> GetQuestion(int id)
{
Question question = await db.Questions.FindAsync(id);
if (question == null)
{
return NotFound();
}
return Ok(question);
}
// PUT: api/Questions/5
[ResponseType(typeof(void))]
public async Task<IHttpActionResult> PutQuestion(int id, Question question)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
if (id != question.QuestionId)
{
return BadRequest();
}
db.Entry(question).State = EntityState.Modified;
try
{
await db.SaveChangesAsync();
}
catch (DbUpdateConcurrencyException)
{
if (!QuestionExists(id))
{
return NotFound();
}
else
{
throw;
}
}
return StatusCode(HttpStatusCode.NoContent);
}
// POST: api/Questions
[ResponseType(typeof(Question))]
public async Task<IHttpActionResult> PostQuestion(Question question)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
db.Questions.Add(question);
await db.SaveChangesAsync();
return CreatedAtRoute("DefaultApi", new { id = question.QuestionId }, question);
}
// DELETE: api/Questions/5
[ResponseType(typeof(Question))]
public async Task<IHttpActionResult> DeleteQuestion(int id)
{
Question question = await db.Questions.FindAsync(id);
if (question == null)
{
return NotFound();
}
db.Questions.Remove(question);
await db.SaveChangesAsync();
return Ok(question);
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
db.Dispose();
}
base.Dispose(disposing);
}
private bool QuestionExists(int id)
{
return db.Questions.Count(e => e.QuestionId == id) > 0;
}
}