实体框架在我的WebAPI Mvc4解决方案中不可用

Question

我用流利的api制作了实体框架代码优先。

我有一个web api控制器：

public class NewsController : ApiController
{
private TrafficTheoryContext db = new TrafficTheoryContext();
// GET api/News
public IEnumerable<News> GetNews()
{
//return new List<News> {
//  new News{ Title = "Featuring Azure ACS Authentication", Subtile="Hello "}};
return db.News.AsEnumerable();
}
} 

如果我提出获取请求，我会得到一个错误：

此XML文件似乎没有任何关联的样式信息。文档树如下所示。

<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'.
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace/>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Type 'System.Data.Entity.DynamicProxies.News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C' with data contract name 'News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.
</ExceptionMessage>
<ExceptionType>
System.Runtime.Serialization.SerializationException
</ExceptionType>
<StackTrace>
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeAndVerifyType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, Boolean verifyKnownType, RuntimeTypeHandle declaredTypeHandle, Type declaredType) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithXsiType(XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle objectTypeHandle, Type objectType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle, Type declaredType) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle) at WriteArrayOfNewsToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , CollectionDataContract ) at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithoutXsiType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObject(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.WriteObject(XmlWriter writer, Object graph) at System.Net.Http.Formatting.XmlMediaTypeFormatter.<>c__DisplayClass7.<WriteToStreamAsync>b__6() at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)
</StackTrace>
</InnerException>
</Error>

如果我只是返回一个新闻列表，它工作罚款。我注意到类被附加了某种我不知道是什么的名字？

我该怎么做才能让webapi正常工作？

Answer 1

我相信您之所以会出现此异常，是因为为实体生成了动态代理。如果查看异常消息，则实际上并没有序列化News类型，而是序列化System.Data.Entity.DynamicProxies.News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C类型。实体框架为您创建了此类型，以支持延迟加载。您可以在此处找到有关动态代理的更多详细信息：http://msdn.microsoft.com/en-US/data/jj592886.我不太了解WebAPI，但这个例外实际上说明了需要做什么：

键入"System.Data.Entity.DynamicProxies.News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C"和数据协定名称'新闻_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies'不应为考虑使用DataContractResolver或将任何未知类型静态添加到已知类型列表中，例如使用KnownTypeAttribute属性，或者将它们添加到传递给DataContractSerializer的已知类型列表中

由于类型是自动创建的，因此不能放置属性。因此，我将重点关注"考虑使用DataContractResolver"one_answers"将它们添加到传递给DataContractSerializer的已知类型列表中"部分。

顺便问一下，你用的是什么版本的EF？我想我以前看到过这个问题，它在EF5 RTM中得到了修复。

Answer 2

在我的Mcv5项目中，当我禁用代理创建时，我也遇到了同样的问题——一切都像魅力一样。我希望它也能帮助你。

DbContext.Configuration.ProxyCreationEnabled = false;

Answer 3

使用.ToList()代替.AsEnumerable。我也很好奇你是如何创建和销毁数据上下文的。