ASP.NET WEB API處理2相關表格

Question

我目前正在使用ASP.NET MVC WEB-API。

首先我使用WEB-API和實體框架創建一個控制器。 使用我的tbl_User，通過.../api/User =>調用它，它工作得很好。 （無外資鍵存在）

做同樣的我tbl_Entry（包括tbl_EntryType），我收到以下錯誤：

<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> 
Type 'System.Data.Entity.DynamicProxies.tbl_Entry_EAF4A2D5587BA15D1CE736067702C5D158ADFB6D6C49D43B66F64E14A4EBE8AC' with data contract name 'tbl_Entry_EAF4A2D5587BA15D1CE736067702C5D158ADFB6D6C49D43B66F64E14A4EBE8AC:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver 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 DataContractSerializer. 
</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 WriteArrayOftbl_EntryToXml(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.<>c__DisplayClass7.<WriteToStreamAsync>b__6() at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token) 
</StackTrace> 
</InnerException> 
</Error> 

如何解決使用tbl_Entry就此問題與外國包括tbl_EntryType鍵？

Answer 1

它是因爲你的表是相互引用的，所以它本質上是在嘗試序列化時創建一個永無止境的循環。根據您的數據的複雜性，我總是建議使用ViewModels。它迫使你只公開你想發送的列，並用序列化來解決問題。如果您不打算重複使用視圖模型，只需返回一個包含所需數據的新對象。

我不知道你的應用程序的結構，但你可以做這樣的事情

public object GetDealership(int id) 
    { 
     return Db.Dealerships.Find(id).Select(x => new { 
      x.SomeProperty, 
      x.RelationshipObject.SomeProperty 
     }); 
    } 

或者使用的ViewModels（推薦Automapper），但純樸的緣故

public ViewModel GetDealership(int id) 
    { 
     return Db.Dealerships.Find(id).Select(x => new ViewModel { 
      x.SomeProperty, 
      x.RelationshipObject.SomeProperty 
     }); 
    }