防止对象图序列化的循环引用

Posted 2023-05-07

【中文标题】防止对象图序列化的循环引用

【英文标题】：Circular references preventing serialization of object graph

【发布时间】：2013-08-25 21:20:58

【问题描述】：

我有一个涉及杂草和杂草家族的简单数据模型。

WeedFamily <-1---*-> Weed（WeedFamily 和 Weed 是一对多的关系）

我正在尝试完成我的第一个 ApiController，以便我可以轻松地将我的数据作为 JSON 检索到 AngularJS 应用程序。当我在我的应用程序中访问 /WeedAPI/ URL 时，我收到以下错误。我很确定问题是我在Weed 和WeedFamily 之间有循环引用。

我应该如何更改我的数据模型，以便 JSON 序列化能够正常工作，同时保持Weed-WeedFamily 关系的双向质量？

（即。我仍然希望能够构建如下表达式：

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

和

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

)

错误：

<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>

我的数据：

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"])

        ;
    

我的模型类：

[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>();
    

最后是 ApiController：

public class WeedAPIController : ApiController

    //
    // GET: /WeedAPI/

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

【问题讨论】：

你为什么要覆盖ToString()？您可能只想使用 [DebuggerDisplay] 属性。

【参考方案1】：

将[DataContract(IsReference = true)] 添加到具有循环引用的对象中。

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

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

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

【讨论】：

我需要导入才能使用该属性吗？ The type or namespace name 'DataContractAttribute' could not be found

是的，它在 System.Runtime.Serialization 命名空间中

原来我需要在我的 VS 项目中添加 System.Runtime.Serialization.dll 作为参考：***.com/questions/7401795/namespace-for-datacontract 在我这样做之后，我的序列化工作正常！谢谢。

如果我使用 json 序列化器会怎样