Web API2 序列化异常

Question

我有一个使用 EF 搭建的 web api2 应用程序。

我正在尝试序列化以下类（其中包含延迟加载的导航属性）：

namespace Models
{
    public class Speciality
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int SpecialityId { get; set; }

        public string Name { get; set; }

        public virtual ICollection<Doctor> Doctors { get; set; }
        public virtual ICollection<MedicalFacility> MedicalFacilities { get; set; }
    }
} 

这是我的控制器：

namespace FindAMedicService.Controllers
{

    public class SpecialitiesController : ApiController
    {
        private ApplicationDbContext db = new ApplicationDbContext();

        // GET: api/Specialities
        public IQueryable<Speciality> GetSpeciality()
        {
            return db.Speciality;
        }
    }
}

当我尝试访问此特定服务以获取“专业”列表时，我收到以下错误：

<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>
Type 'System.Data.Entity.DynamicProxies.Speciality_DC264D6DBBAF52FB19E27F20DCC47DA1141620CEC0CCAF6E2DEF4D8907FA7C8C' with data contract name 'Speciality_DC264D6DBBAF52FB19E27F20DCC47DA1141620CEC0CCAF6E2DEF4D8907FA7C8C: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 WriteArrayOfSpecialityToXml(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.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>

在我的 Specialty 类（Doctors、MedicalFacilities）中没有两个导航属性之前，我没有出现此错误。

非常感谢任何帮助。

Answer 1

简单回顾一下 - 你为什么返回 IQueryable 和你的实体模型？

在我看来，您应该将您的实体模型转换为某种仅具有所需属性的 DTO + 将操作签名更改为 IEnumerable<T>。

序列化程序不知道如何序列化 EF 为您的 virtual 属性创建的动态代理。

Answer 2

请在 webconfig 中输入以下代码 sn-p:

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreservReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);

Answer 3

原因可能是您的导航属性是接口，因此当您访问服务时，它不知道要使用什么具体类型。将其更改为 List 看看是否有帮助？

Answer 4

使用 Serializable() 属性。 试试这个：

namespace Models
{
    [Serializable]
    public class Speciality
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int SpecialityId { get; set; }

        public string Name { get; set; }

        public virtual ICollection<Doctor> Doctors { get; set; }
        public virtual ICollection<MedicalFacility> MedicalFacilities { get; set; }
    }
} 

Answer 5

最终起作用的是禁用 ProxyCreationEnabled。

所以在我的控制器中，我现在有以下代码：

public class SpecialitiesController : ApiController
    {
        private ApplicationDbContext db = new ApplicationDbContext();

        public SpecialitiesController()
        {
            db.Configuration.ProxyCreationEnabled = false;
        }

        // GET: api/Specialities
        public IQueryable<Speciality> GetSpeciality()
        {
            return db.Speciality;
        }
    }

这确实意味着我必须使用 .include() 急切加载我想使用的任何导航属性。