Entity framework 在ASP.NET Web API中序列化对象时出现循环引用错误_Entity Framework_Asp.net Mvc 4_Serialization_Asp.net Web Api_Circular Reference

Entity framework 在ASP.NET Web API中序列化对象时出现循环引用错误

entity-framework asp.net-mvc-4 serialization asp.net-web-api

Entity framework 在ASP.NET Web API中序列化对象时出现循环引用错误,entity-framework,asp.net-mvc-4,serialization,asp.net-web-api,circular-reference,Entity Framework,Asp.net Mvc 4,Serialization,Asp.net Web Api,Circular Reference,我正在用C#编写一个Web API项目，它使用实体框架从数据库中提取数据，将其序列化并发送给客户机我的项目有两个类，Post和Comment（来自Post的外键）这些是我的课邮班： public partial class Post { public Post() { this.Attachment = new HashSet<Attachment>(); this.Comment = new HashSet<Comment

我正在用C#编写一个Web API项目，它使用实体框架从数据库中提取数据，将其序列化并发送给客户机

我的项目有两个类，Post和Comment（来自Post的外键）

这些是我的课

邮班：

public partial class Post
{
    public Post()
    {
        this.Attachment = new HashSet<Attachment>();
        this.Comment = new HashSet<Comment>();
    }

    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public System.DateTime Created { get; set; }
    public Nullable<System.DateTime> Modified { get; set; }

    public virtual ICollection<Attachment> Attachment { get; set; }
    public virtual ICollection<Comment> Comment { get; set; }
}

我的问题是，当我试图通过Web API获取帖子时，它向我抛出以下错误：

Object graph for type 'APIServer.Models.Comment' contains cycles and cannot be serialized if reference tracking is disabled.

当我试图通过Web API获取评论时，错误如下：

Object graph for type 'System.Collections.Generic.HashSet`1[[APIServer.Models.Comment, APIServer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]'  contains cycles and cannot be serialized if reference tracking is disabled.

[OperationContract]
Comment FindComment(string criteria);

如果我用

[DataContract(IsReference = true)]

错误消失，但序列化只返回注释的ID，而忽略其他字段

对如何解决这个问题有什么建议吗

提前感谢,

Lester

您可以通过从Post属性定义中删除virtual来禁用注释类上的延迟加载

public partial class Comment
{
    public int CommentId { get; set; }
    public string Content { get; set; }
    public System.DateTime Posted { get; set; }
    public bool Approved { get; set; }
    public int AnswersTo { get; set; }
    public int PostId { get; set; }

    public Post Post { get; set; }
}

这应该可以解决循环引用异常。

这里有两种解决方案 解决方案#1:

我也有同样的问题，所以我用

DataContract

装饰了我的类，并且像你提到的那样用

DataMember

装饰了成员。但是，我不喜欢直接编辑自动生成的代码，因为每次重新生成文件时我都必须重做。为了解决这个问题，我使用了

MetadataType

属性。在你的情况下，看起来是这样的

首先，您将保持自动生成的实体的原样：

public partial class Comment
{
    public int CommentId { get; set; }
    public string Content { get; set; }
    public System.DateTime Posted { get; set; }
    public bool Approved { get; set; }
    public int AnswersTo { get; set; }
    public int PostId { get; set; }

    public virtual Post Post { get; set; }
}

接下来，在另一个文件中，您将创建另一个分部类，并按如下方式装饰它：

[MetadataType(typeof(Metadata))]
[DataContract(IsReference = true)]
public partial class Comment
{
    private class Metadata
    {
        [DataMember]
        public int CommentId { get; set; }
        [DataMember]
        public string Content { get; set; }
        [DataMember]
        public System.DateTime Posted { get; set; }
        [DataMember]
        public bool Approved { get; set; }
        [DataMember]
        public int AnswersTo { get; set; }
        [DataMember]
        public int PostId { get; set; }

        [DataMember]
        public virtual Post Post { get; set; } // you can remove "virtual" if you wish
    }
}

//From http://blogs.msdn.com/b/sowmy/archive/2006/03/26/561188.aspx and https://stackoverflow.com/questions/4266008/endless-loop-in-a-code-sample-on-serialization
public class ReferencePreservingDataContractFormatAttribute : Attribute, IOperationBehavior
{
    public void AddBindingParameters(OperationDescription description, BindingParameterCollection parameters)
    {
    }

    public void ApplyClientBehavior(OperationDescription description, System.ServiceModel.Dispatcher.ClientOperation proxy)
    {
        IOperationBehavior innerBehavior = new ReferencePreservingDataContractSerializerOperationBehavior(description);
        innerBehavior.ApplyClientBehavior(description, proxy);
    }

    public void ApplyDispatchBehavior(OperationDescription description, System.ServiceModel.Dispatcher.DispatchOperation dispatch)
    {
        IOperationBehavior innerBehavior = new ReferencePreservingDataContractSerializerOperationBehavior(description);
        innerBehavior.ApplyDispatchBehavior(description, dispatch);
    }

    public void Validate(OperationDescription description)
    {
    }

}
class ReferencePreservingDataContractSerializerOperationBehavior : DataContractSerializerOperationBehavior
{
    public ReferencePreservingDataContractSerializerOperationBehavior(OperationDescription operationDescription) : base(operationDescription) { }
    public override XmlObjectSerializer CreateSerializer(Type type, string name, string ns, IList<Type> knownTypes)
    {
        return new DataContractSerializer(type, name, ns, knownTypes,
            0x7FFF, //maxItemsInObjectGraph
            false,  //ignoreExtensionDataObject
            true,   //preserveObjectReferences
            null    //dataContractSurrogate
            );
    }

    public override XmlObjectSerializer CreateSerializer(Type type, XmlDictionaryString name, XmlDictionaryString ns, IList<Type> knownTypes)
    {
        return new DataContractSerializer(type, name, ns, knownTypes,
            0x7FFF, //maxItemsInObjectGraph
            false,  //ignoreExtensionDataObject
            true,   //preserveObjectReferences
            null    //dataContractSurrogate
            );
    }
}

MetadataType

基本上会将

元数据

好友类中的属性添加到

注释

中同名的属性中（不是直接添加，但出于我们的目的，它已经足够接近了……这是另一篇文章的主题）。当然，如果您的

注释

实体发生了更改，您需要相应地更新它

解决方案#2:

与直接编辑自动生成的文件相比，每次进行更改时都必须编辑第二个文件只是一个小小的改进。幸运的是，还有另一种更容易维护的方法。可以找到详细信息，但作为一个总结，您需要做的就是使用一个附加属性，

ReferencePreservingDataContractFormat

来修饰您的

OperationContract

。请注意，该页面上提供的代码中有一个微小的错误，它将导致无限递归。正如在文章中所指出的，修复非常简单：只需创建一个新的

DataContractSerializer

这种方法的优点是，无论您对

注释做了多少更改，您仍然不需要更新任何内容
作为代码示例，假设您正在使用Comment
，如下所示：
Object graph for type 'System.Collections.Generic.HashSet`1[[APIServer.Models.Comment, APIServer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]'  contains cycles and cannot be serialized if reference tracking is disabled.

[OperationContract]
Comment FindComment(string criteria);

您只需添加
[OperationContract]
[ReferencePreservingDataContractFormat]
Comment FindComment(string criteria);

然后在其他地方需要定义ReferencePreservingDataContractFormat
，如下所示：
[MetadataType(typeof(Metadata))]
[DataContract(IsReference = true)]
public partial class Comment
{
    private class Metadata
    {
        [DataMember]
        public int CommentId { get; set; }
        [DataMember]
        public string Content { get; set; }
        [DataMember]
        public System.DateTime Posted { get; set; }
        [DataMember]
        public bool Approved { get; set; }
        [DataMember]
        public int AnswersTo { get; set; }
        [DataMember]
        public int PostId { get; set; }

        [DataMember]
        public virtual Post Post { get; set; } // you can remove "virtual" if you wish
    }
}

//From http://blogs.msdn.com/b/sowmy/archive/2006/03/26/561188.aspx and https://stackoverflow.com/questions/4266008/endless-loop-in-a-code-sample-on-serialization
public class ReferencePreservingDataContractFormatAttribute : Attribute, IOperationBehavior
{
    public void AddBindingParameters(OperationDescription description, BindingParameterCollection parameters)
    {
    }

    public void ApplyClientBehavior(OperationDescription description, System.ServiceModel.Dispatcher.ClientOperation proxy)
    {
        IOperationBehavior innerBehavior = new ReferencePreservingDataContractSerializerOperationBehavior(description);
        innerBehavior.ApplyClientBehavior(description, proxy);
    }

    public void ApplyDispatchBehavior(OperationDescription description, System.ServiceModel.Dispatcher.DispatchOperation dispatch)
    {
        IOperationBehavior innerBehavior = new ReferencePreservingDataContractSerializerOperationBehavior(description);
        innerBehavior.ApplyDispatchBehavior(description, dispatch);
    }

    public void Validate(OperationDescription description)
    {
    }

}
class ReferencePreservingDataContractSerializerOperationBehavior : DataContractSerializerOperationBehavior
{
    public ReferencePreservingDataContractSerializerOperationBehavior(OperationDescription operationDescription) : base(operationDescription) { }
    public override XmlObjectSerializer CreateSerializer(Type type, string name, string ns, IList<Type> knownTypes)
    {
        return new DataContractSerializer(type, name, ns, knownTypes,
            0x7FFF, //maxItemsInObjectGraph
            false,  //ignoreExtensionDataObject
            true,   //preserveObjectReferences
            null    //dataContractSurrogate
            );
    }

    public override XmlObjectSerializer CreateSerializer(Type type, XmlDictionaryString name, XmlDictionaryString ns, IList<Type> knownTypes)
    {
        return new DataContractSerializer(type, name, ns, knownTypes,
            0x7FFF, //maxItemsInObjectGraph
            false,  //ignoreExtensionDataObject
            true,   //preserveObjectReferences
            null    //dataContractSurrogate
            );
    }
}

//来自http://blogs.msdn.com/b/sowmy/archive/2006/03/26/561188.aspx 及https://stackoverflow.com/questions/4266008/endless-loop-in-a-code-sample-on-serialization
公共类ReferencePreservingDataContractFormatAttribute:属性，IOperationBehavior
{
public void AddBindingParameters（操作说明、BindingParameterCollection参数）
{
}
public void ApplyClientBehavior（操作描述，System.ServiceModel.Dispatcher.ClientOperation代理）
{
IOperationBehavior innerBehavior=新引用保留数据契约序列化属性行为（描述）；
ApplyClientBehavior（描述，代理）；
}
public void ApplyDispatchBehavior（操作描述，System.ServiceModel.Dispatcher.DispatchOperation dispatch）
{
IOperationBehavior innerBehavior=新引用保留数据契约序列化属性行为（描述）；
ApplyDispatchBehavior（描述、分派）；
}
公共无效验证（操作说明）
{
}
}
类referencePreservingDataContractSerializeRopection行为：DataContractSerializeRopection行为
{
公共引用保留DataContractSerializePropertyBehavior（OperationDescription OperationDescription）：基（OperationDescription）{}
公共重写XmlObjectSerializer CreateSerializer（类型类型、字符串名称、字符串ns、IList knownTypes）
{
返回新的DataContractSerializer（类型、名称、ns、knownTypes、，
0x7FFF，//maxItemsInObjectGraph
false，//ignoreExtensionDataObject
true，//preserveObjectReferences
null//datacontractsubrogate
);
}
公共重写XmlObjectSerializer CreateSerializer（类型类型、XmlDictionaryString名称、XmlDictionaryString ns、IList knownTypes）
{
返回新的DataContractSerializer（类型、名称、ns、knownTypes、，
0x7FFF，//maxItemsInObjectGraph
false，//ignoreExtensionDataObject
true，//preserveObjectReferences
null//datacontractsubrogate
);
}
}

就这样
任何一种方法都可以很好地工作——选择一种适合您的方法。
解决方案2应该适用于WCF项目，我在这里测试了它不起作用。@IcyBrk-您一定做错了什么，因为我一直在WCF项目中使用它，而且它工作得很好。这解决了自引用导航属性吗？