Webapi exception when Entity Framework has bidirectional associations - entity-framework

Question

I've created entity framework 6 boilerplate code from a database using code first and I can retrieve my data fine and see all my tables in list objects just fine, so I know retrieval is fine and any lazy loading is working.
However when returning the list from a webapi rest service it only works for my simple class (BikeStation below) which has no associated lists, when I try my classes which have references to other objects, it generates an exception to do with data contracts and seems to be linked to circular references
Here are my classes:
public partial class BikeStation
{
public int Id { get; set; }
public string CentreName { get; set; }
public string StationName { get; set; }
}
public partial class Bike
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
public Bike()
{
BikeStats = new HashSet<BikeStat>();
}
public string ShortBikeName { get; set; }
public bool Active { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<BikeStat> BikeStats { get; set; }
}
public partial class BikeStat
{
public int Id { get; set; }
public DateTime StatDate { get; set; }
public virtual Bike Bike { get; set; }
}
This works:
public IEnumerable<BikeStation> Get()
{
using (var db = new BikesContext())
{
var a = db.BikeStations.ToList();
return a;
}
}
However, changing to either of the other two gets the list fine but then fails to serialise the data:
public IEnumerable<Bike> Get()
{
using (var db = new BikesContext())
{
var a = db.Bikes.ToList();
return a;
}
}
If I remove the reference to the bike or bikestats in either of my other classes, it works just fine.
The error is this, and I don't really understand why it's trying to serialise as XML either. Any help would be appreciated.
<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.Bike_16DB1847327CF3674DCB6407C4CCB0E41EA43002E17C91F35F5B4716F57DAD1D' with data contract name 'Bike_16DB1847327CF3674DCB6407C4CCB0E41EA43002E17C91F35F5B4716F57DAD1D:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver if you are using DataContractSerializer 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 the serializer.</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 WriteArrayOfBikeToXml(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.SerializeAndVerifyType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, Boolean verifyKnownType, RuntimeTypeHandle declaredTypeHandle, Type declaredType)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithXsiTypeAtTopLevel(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle originalDeclaredTypeHandle, Type graphType)
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.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)
at System.Net.Http.Formatting.XmlMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()</StackTrace></InnerException></Error>
I then changed my code to explicitly convert the code using a custom class, which works but isn't ideal:
var newData = d.Select(x => new Bike()
{
Active = x.Active,
ShortBikeName = x.ShortBikeName,
BikeStats = (x.BikeStats.Select(item => new BikeStat()
{
Id = item.Id,
StatDate = item.StatDate
}).ToList() as ICollection<BikeStat>)
}).ToList();
This works, but is a bit pants. So I changed the serialisation to this:
var d = db.Bikes.Include("BikeStats").ToList();
string s = JsonConvert.SerializeObject(d,
Formatting.Indented,
new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Ignore, PreserveReferencesHandling=PreserveReferencesHandling.Objects });
return s;
Which works, but it doesn't. It adds "\r\n" as a string to the response, turns all quote marks into \", puts '$' in front of some values and Chrome still thinks it's XML.
I changed the class to have this and it all magically works. Why? and is there a better way so that I can still access Bike from BikeStat?
[JsonIgnore]
public Bike Bike { get; set; }

Answer 1

Try Changing your code to look like this
public class BikeStation
{
public int Id { get; set; }
public string CentreName { get; set; }
public string StationName { get; set; }
}
public class Bike
{
public string ShortBikeName { get; set; }
public bool Active { get; set; }
public IEnumerable<BikeStat> BikeStats { get; set; }
}
public class BikeStat
{
public int Id { get; set; }
public DateTime StatDate { get; set; }
public Bike Bike { get; set; }
}