Question

我使用流畅的api制作了实体框架代码。

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();
    }
}

如果我发出获取请求，我会收到错误：

此XML文件似乎没有与之关联的任何样式信息。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>

如果我只是返回一份新闻列表，那就会被罚款。我注意到这些文章附有某种我不知道的名字？

如何让webapi工作？

Answer 1

我相信您会因为为您的实体生成动态代理而获得此异常。如果查看异常消息，则实际上并不是序列化新闻类型，而是System.Data.Entity.DynamicProxies.News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C类型。此类型是由Entity Framework为您创建的，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，但例外实际上说明了需要做什么：

输入带有数据合约名称的'System.Data.Entity.DynamicProxies.News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C' 'News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C：HTTP：//schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' 不是预期的。考虑使用DataContractResolver或将任何静态未知的类型添加到已知类型列表中 - 例如，通过使用KnownTypeAttribute 属性或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，因此无法放置属性。因此，我将重点关注“考虑使用DataContractResolver”和“将它们添加到传递给DataContractSerializer的已知类型列表”部分。

顺便问一下您使用的EF版本是什么？我想我之前看过这个问题，它已在EF5 RTM中修复。

Answer 2

我在Mcv5项目中遇到同样的问题，当我禁用代理创建时，每件事情都像魅力一样。我希望它也能帮到你。

DbContext.Configuration.ProxyCreationEnabled = false;

Answer 3

而不是.AsEnumerable，使用.ToList（）。我也很好奇你是如何创建和破坏数据上下文的。

实体框架在我的WebAPI Mvc4解决方案中无法使用

3 个答案: