循環引用防止對象圖的序列化

Question

我有一個涉及雜草和雜草家庭的簡單數據模型。

WeedFamily <-1---*-> Weed （WeedFamily和Weed有一對多的關系）

我正在嘗試完成我的第一個ApiController，以便我可以輕松地將我的數據檢索為AngularJS應用程序的JSON。 當我在我的應用程序中訪問/WeedAPI/ URL時，出現以下錯誤。 我很確定問題是我在Weed和WeedFamily之間有循環引用。

我應該如何更改我的數據模型，以便JSON序列化能夠在保持Weed - WeedFamily關系的雙向質量的同時WeedFamily ？

（即我仍然希望能夠構建如下表達式：

 WeedData.GetFamilies()["mustard"].Weeds.Count

和

WeedData.GetWeeds()[3].Family.Weeds

）

錯誤：

<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>
            Object graph for type 'WeedCards.Models.WeedFamily' contains cycles and cannot be serialized if reference tracking is disabled.
        </ExceptionMessage>
        <ExceptionType>
            System.Runtime.Serialization.SerializationException
        </ExceptionType>
        <StackTrace>
            at System.Runtime.Serialization.XmlObjectSerializerWriteContext.OnHandleReference(XmlWriterDelegator xmlWriter, Object obj, Boolean canContainCyclicReference) at WriteWeedToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , ClassDataContract ) at System.Runtime.Serialization.ClassDataContract.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.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDecl...etc
        </StackTrace>
    </InnerException>
</Error>

我的數據：

public class WeedData
{
    public static Dictionary<string,WeedFamily> GetFamilies(){
        return new Dictionary<string,WeedFamily>
        {
             {"mustard",new WeedFamily("Mustard","Brassicaceae")}
            ,{"pigweed",new WeedFamily("Pigweed","Amaranthus")}
            ,{"sunflower",new WeedFamily("Sunflower","Asteraceae")}
        };
    }

    public static List<Weed> GetWeeds(){
        var Families = GetFamilies();
        return new List<Weed>
        {
             new Weed("Hairy Bittercress","Cardamine hirsuta",Families["mustard"])
            ,new Weed("Little Bittercress","Cardamine oligosperma",Families["mustard"])
            ,new Weed("Shepherd's-Purse","Capsella bursa-pastoris",Families["mustard"])
            ,new Weed("Wild Mustard","Sinapis arvensis / Brassica kaber",Families["mustard"])
            ,new Weed("Wild Radish","Raphanus raphanistrum",Families["mustard"])
            ,new Weed("Radish","Raphanus sativus",Families["mustard"])
            ,new Weed("Redroot Pigweed","Amaranthus retroflexus",Families["pigweed"])
            ,new Weed("Prickly Lettuce","Lactuca serriola",Families["sunflower"])
            ,new Weed("Spiny Sowthistle","Sonchus asper",Families["sunflower"])
            ,new Weed("Annual Sowthistle","Sonchus oleraceus",Families["sunflower"])

        };
    }
}

我的模型類：

[Serializable]
public class Weed
{
    public string CommonName;
    public string LatinName;
    public List<WeedPhoto> Photos;
    public WeedFamily Family;

    public Weed(string commonName, string latinName)
    {
        CommonName = commonName;
        LatinName = latinName;
    }

    public Weed(string commonName, string latinName, WeedFamily family)
    {
        CommonName = commonName;
        LatinName = latinName;
        Family = family;
        Family.Weeds.Add(this);
    }

    override public string ToString()
    {
        return CommonName + " (" + LatinName + ")";
    }
}

和

[Serializable]
public class WeedFamily
{
    public string CommonName;
    public string LatinName;
    public List<Weed> Weeds;

    public WeedFamily(string commonName, string latinName)
    {
        CommonName = commonName;
        LatinName = latinName;
        Weeds = new List<Weed>();
    }
}

最后，ApiController：

public class WeedAPIController : ApiController
{
    //
    // GET: /WeedAPI/

    public IEnumerable<Weed> GetAllWeeds()
    {
        return WeedData.GetWeeds();
    }

}

Answer 1

將[DataContract(IsReference = true)]到具有循環引用的對象。

[Serializable]
[DataContract(IsReference = true)]
public class WeedFamily

[Serializable]
[DataContract(IsReference = true)]
public class Weed

請參閱http://msdn.microsoft.com/en-us/library/vstudio/hh241056(v=vs.100).aspx