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Asked: 2026-06-12T06:05:52+00:00

I have made Entity Framework Code First with fluent api. I have a web

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I have made Entity Framework Code First with fluent api.

I have a web api controller:

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();
    }
}

If i make a get request i get an error:

This XML file does not appear to have any style information associated with it. The document tree is shown below.

<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>

If i just return a List of News it work fines. I noticed the clases are appended with some kind of name that i do not know what is?

What do i do to get the webapi to work?

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1 Answer

  1. Editorial Team

    I believe that you get this exception because of dynamic proxies generated for your entities. If you look at the exception message you don’t actually serialize News type but the System.Data.Entity.DynamicProxies.News_786DE29B12691F869E9C9DF523A808EABE06546C3FCE3354F77875B83B9EB51C type. This type was created for you by Entity Framework to support lazy loading. You can find more details about dynamic proxies here: http://msdn.microsoft.com/en-US/data/jj592886.
    I don’t know WebAPI very well but the exception actually says what’s need to be done:

    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.

    Since the type is created automatically you cannot put the attribute. Therefore I would focus on the “Consider using a DataContractResolver” and “adding them to the list of known types passed to DataContractSerializer” parts.

    Btw what version of EF are you using? I think I saw this issue before and it was fixed in EF5 RTM.

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