WebAPI2 + Angular http GET - 返回IEnumerable 。无法序列化内容类型'application / json的响应正文

I'm learning this as we speak and find some of this pretty strange and hard ;)

我正在学习这个,因为我们说话,并发现其中一些非常奇怪和困难;)

Here is the rest service call in Angular:

这是Angular中的其余服务调用:

$scope.categories = [];
    $scope.selectedCategory = null;

    $http({
            method: 'GET',
            url: './api/file/GetCategories',
            accept: 'application/json'
        })
        .success(function(result) {
        $scope.categories = result;
    });

Here is the service I'm trying to fetch : (C# - FileController.cs)

这是我想要获取的服务:(C# - FileController.cs)

public IEnumerable<Category> GetCategories()
    {
        return FileServices.GetCategoriesForUser();

    }

Fileservices method :

Fileservices方法:

public static IEnumerable<Category> GetCategoriesForUser()
    {
        User currentUser = UserServices.GetLoggedInUser();
        IEnumerable<Category> userCategories;
        using (var context = new PhotoEntities())
        {
            userCategories = context.Categories.Where(c => c.UserId == currentUser.Id);
        }
        return userCategories;
    }

The issue is that it probably don't recognize it as JSON at all, but, alas! Here is the whole response-error msg :

问题是它根本不会将它识别为JSON,但是,唉!这是整个响应错误消息:

{"Message":"An error has occurred.","ExceptionMessage":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.","ExceptionType":"System.InvalidOperationException","StackTrace":null,"InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Error getting value from 'Categories' on 'System.Data.Entity.DynamicProxies.User_523AFE24D26493BB74E43EAA23AAEBFD40D7EABFCAA3A6105EB951B365E60A04'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":"   at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   at System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)\r\n   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\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__1b.MoveNext()","InnerException":{"Message":"An error has occurred.","ExceptionMessage":"The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.","ExceptionType":"System.ObjectDisposedException","StackTrace":"   at System.Data.Entity.Core.Objects.ObjectContext.get_Connection()\r\n   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)\r\n   at System.Data.Entity.Core.Objects.ObjectQuery`1.Execute(MergeOption mergeOption)\r\n   at System.Data.Entity.Core.Objects.DataClasses.EntityCollection`1.Load(List`1 collection, MergeOption mergeOption)\r\n   at System.Data.Entity.Core.Objects.DataClasses.EntityCollection`1.Load(MergeOption mergeOption)\r\n   at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.Load()\r\n   at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.DeferredLoad()\r\n   at System.Data.Entity.Core.Objects.Internal.LazyLoadBehavior.LoadProperty[TItem](TItem propertyValue, String relationshipName, String targetRoleName, Boolean mustBeNull, Object wrapperObject)\r\n   at System.Data.Entity.Core.Objects.Internal.LazyLoadBehavior.<>c__DisplayClass7`2.<GetInterceptorDelegate>b__1(TProxy proxy, TItem item)\r\n   at System.Data.Entity.DynamicProxies.User_523AFE24D26493BB74E43EAA23AAEBFD40D7EABFCAA3A6105EB951B365E60A04.get_Categories()\r\n   at GetCategories(Object )\r\n   at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)"}}}

3 个解决方案

#1

Try adding this to the Register() function in the config file in your App_Start folder:

尝试将其添加到App_Start文件夹中配置文件中的Register()函数:

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

I had a similar problem and this fixed it for me. This was taken from: http://social.msdn.microsoft.com/Forums/vstudio/en-US/a5adf07b-e622-4a12-872d-40c753417645/

我有一个类似的问题,这为我修好了。这取自:http://social.msdn.microsoft.com/Forums/vstudio/en-US/a5adf07b-e622-4a12-872d-40c753417645/

#2

I've gotten in the habit of returning an HttpResponseMessage so that I have direct control over the status and content type. Here's some code that will do that for you.

我已经养成了返回HttpResponseMessage的习惯,这样我就可以直接控制状态和内容类型了。这里有一些代码可以帮到你。

public class StuffController : ApiController
{
    public HttpResponseMessage Get()
    {
        List<SomeModel> models = ReadModels();
        return GetJsonResponse(models);
    }
}

public static HttpResponseMessage GetJsonResponse(object serializableObject)
{
    string jsonText = JsonConvert.SerializeObject(serializableObject, Formatting.Indented);
    HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
    response.Content = new StringContent(jsonText, Encoding.UTF8, "text/plain");

    return response;
}

#3

Just use List:

只需使用List:

public static List<Category> GetCategoriesForUser()
    {
        User currentUser = UserServices.GetLoggedInUser();
        IEnumerable<Category> userCategories = new List<Category>();
        using (var context = new PhotoEntities())
        {
            userCategories.addRange(context.Categories.Where(c => c.UserId == currentUser.Id).toList());
        }
        return userCategories;
    }

IEnumerable is an interface, you can't create instance of interface.

IEnumerable是一个接口,不能创建接口实例。

Edit: Changed to addRange method. And change your service from IEnumerable to List:

编辑:更改为addRange方法。并将您的服务从IEnumerable更改为List:

public List<Category> GetCategories()

#1