WebAPI OData 错误 ObjectContent 类型无法序列化内容类型“application/json ...”的响应正文

Question

这个要杀了我。这里的文章和网络都没有帮助。

首先，我正在使用 .Net 4.5 开发 ASP.Net WebForms（不是 MVC）。我找到了一个great article，它可以帮助您将 OData 提要添加到您的 WebForms 站点。它像冠军一样工作。我能够创建一个 EMPTY Web 应用程序并让它工作。但是，我注意到它没有使用我通过this article 创建的最新（并且据说更容易）EntitySetController。两人分别工作。然后我按摩了原始文章，看看它是否可以处理EntitySetController，它可以。按照建议使用Fiddler 来测试OData 及其过滤。哦，快乐的一天。

我的下一步是将其添加到我现有的 ASP.Net 4.5 WebForms 应用程序中。让它有点工作。一切都编译好了，我可以调用locallhost:55777/kid，它按预期返回Products：

<workspace>
  <atom:title type="text">Default</atom:title>
  <collection href="Products">
    <atom:title type="text">Products</atom:title>
  </collection>
</workspace>

然后我尝试Get 或GetEntityByKey 方法，它们运行并返回应有的内容。但是，我收到以下错误消息：

{
  "odata.error":{
    "code":"","message":{
      "lang":"en-US","value":"An error has occurred."
    },
    "innererror":{
      "message":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; odata=minimalmetadata; streaming=true; charset=utf-8'.",
      "type":"System.InvalidOperationException",
      "stacktrace":"",
      "internalexception":{
        "message":"No IdLink factory was found. Try calling HasIdLink on the EntitySetConfiguration for 'Products'.",
        "type":"System.InvalidOperationException",
        "stacktrace":"   at System.Web.Http.OData.Builder.EntitySetLinkBuilderAnnotation.BuildIdLink(EntityInstanceContext instanceContext, ODataMetadataLevel metadataLevel)\r\n
                         at System.Web.Http.OData.Builder.EntitySetLinkBuilderAnnotation.BuildEntitySelfLinks(EntityInstanceContext instanceContext, ODataMetadataLevel metadataLevel)\r\n   
                         at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.CreateEntry(SelectExpandNode selectExpandNode, EntityInstanceContext entityInstanceContext)\r\n   
                         at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.WriteEntry(Object graph, ODataWriter writer, ODataSerializerContext writeContext)\r\n   
                         at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.WriteObjectInline(Object graph, IEdmTypeReference expectedType, ODataWriter writer, ODataSerializerContext writeContext)\r\n
                         at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.WriteObject(Object graph, Type type, ODataMessageWriter messageWriter, ODataSerializerContext writeContext)\r\n   
                         at System.Web.Http.OData.Formatter.ODataMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content, HttpContentHeaders contentHeaders)\r\n   
                         at System.Web.Http.OData.Formatter.ODataMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   
                         at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n
                         at System.Runtime.CompilerServices.TaskAwaiter.GetResult()\r\n   
                         at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__10.MoveNext()"
      }
    }
  }
}

控制器是：

using System.Collections.Generic;
using System.Linq;
using System.Web.Http.OData;

namespace BOR.InternalWebsite.Controllers {

    public class ProductsController : EntitySetController<Product, int> {

        static List<Product> products = new List<Product>() {
            new Product() { ID = 1, Name = "Hat", Price = 15, Category = "Apparel" },
            new Product() { ID = 2, Name = "Socks", Price = 5, Category = "Apparel" },
            new Product() { ID = 3, Name = "Scarf", Price = 12, Category = "Apparel" },
            new Product() { ID = 4, Name = "Yo-yo", Price = 4.95M, Category = "Toys" },
            new Product() { ID = 5, Name = "Puzzle", Price = 8, Category = "Toys" },
        };

        public override IQueryable<Product> Get() {
            return products.AsQueryable();
        }

        protected override Product GetEntityByKey(int key) {
            return products.FirstOrDefault(p => p.ID == key);
        }

    }
}

WebApiConfig 是：

using Microsoft.Data.Edm;
using System.Web.Http;
using System.Web.Http.OData.Builder;

namespace BOR.InternalWebsite {

    public static class WebApiConfig {

        public static void Register(HttpConfiguration config) {
            config.EnableQuerySupport();

            ODataModelBuilder modelBuilder = new ODataModelBuilder();
            var products = modelBuilder.EntitySet<Product>("Products");

            IEdmModel model = modelBuilder.GetEdmModel();
            config.Routes.MapODataRoute("ODataRoute", "kid", model);
        }

    }
}

Global.asax.cs 文件的 Application_Start 仅包含以下内容：

WebApiConfig.Register(GlobalConfiguration.Configuration);

只是为了向您展示我在项目中有哪些包，这是我的Packages.config 文件。我知道Microsoft.AspNet.WebApi.* 项目是预发布的。我在当前的稳定版本中有它们，没有什么不同，所以我想我会尝试看看预发布是否能修复它。

<?xml version="1.0" encoding="utf-8"?>
<packages>
    <package id="DynamicDataTemplatesCS" version="1.0.1" targetFramework="net45" />
    <package id="elmah" version="1.2.2" targetFramework="net45" />
    <package id="elmah.corelibrary" version="1.2.2" targetFramework="net45" />
    <package id="EntityFramework" version="5.0.0" targetFramework="net45" />
    <package id="jQuery" version="2.0.3" targetFramework="net45" />
    <package id="jquery.mobile" version="1.3.2" targetFramework="net45" />
    <package id="jQuery.UI.Combined" version="1.10.3" targetFramework="net45" />
    <package id="knockoutjs" version="2.3.0" targetFramework="net45" />
    <package id="Microsoft.AspNet.WebApi" version="5.0.0-rc1" targetFramework="net45" />
    <package id="Microsoft.AspNet.WebApi.Client" version="5.0.0-rc1" targetFramework="net45" />
    <package id="Microsoft.AspNet.WebApi.Core" version="5.0.0-rc1" targetFramework="net45" />
    <package id="Microsoft.AspNet.WebApi.OData" version="5.0.0-rc1" targetFramework="net45" />
    <package id="Microsoft.AspNet.WebApi.WebHost" version="5.0.0-rc1" targetFramework="net45" />
    <package id="Microsoft.Bcl" version="1.1.3" targetFramework="net45" />
    <package id="Microsoft.Bcl.Build" version="1.0.10" targetFramework="net45" />
    <package id="Microsoft.Data.Edm" version="5.6.0" targetFramework="net45" />
    <package id="Microsoft.Data.OData" version="5.6.0" targetFramework="net45" />
    <package id="Microsoft.Net.Http" version="2.2.15" targetFramework="net45" />
    <package id="Newtonsoft.Json" version="5.0.6" targetFramework="net45" />
    <package id="System.Spatial" version="5.6.0" targetFramework="net45" />
    <package id="Twitter.Bootstrap" version="3.0.0" targetFramework="net45" />
</packages>

既然我可以让它独立工作，我认为有些东西会妨碍我。任何有用的帮助将不胜感激！蒂亚！

编辑 == 解决方案

感谢@RaghuRam，唯一需要更改的是 WebApiConfig 的 Register 方法。更新后的工作版本如下：

config.EnableQuerySupport();

ODataConventionModelBuilder modelBuilder = new ODataConventionModelBuilder();
var products = modelBuilder.EntitySet<Product>("Products");

IEdmModel model = modelBuilder.GetEdmModel();
config.Routes.MapODataRoute("ODataRoute", "kid", model);

太棒了！

Answer 1

像这样使用 ODataConventionModelBuilder 而不是 ODataModelBuilder，

var modelBuilder = new ODataConventionModelBuilder ();
var products = modelBuilder.EntitySet<Product>("Products");

IEdmModel model = modelBuilder.GetEdmModel();

ODataModelBuilder 是一个非常低级的类，用于显式配置整个模型时使用。您需要告诉它每个属性、每个导航属性，然后是自链接（id、编辑和读取）和导航链接。

另一方面，ODataConventionModelBuilder 有一些约定可以自动推断这些事情。仅当您偏离约定时，您才需要使用 ODataConventionModelBuilder 显式配置某些内容。

如果您仍然希望使用 ODataModelBuilder 类，您应该编写这样的代码，

ODataModelBuilder modelBuilder = new ODataModelBuilder();
var products = modelBuilder.EntitySet<Product>("Products");
var product = products.EntityType;

product.HasKey(p => p.ID);
product.Property(p => p.Name);
product.Property(p => p.Price);
product.Property(p => p.Category);

products.HasIdLink((ctxt) => ctxt.Url.ODataLink(new EntitySetPathSegment("Products"), new KeyValuePathSegment(ctxt.EntityInstance.ID)));

IEdmModel model = modelBuilder.GetEdmModel();

一旦有了导航属性和相关实体集等，事情就会变得更加复杂。