DbGeography 的反序列化 Entity Framework

Question

我有一个 class Event 和属性类型 DbGeography。

public class Event
{
    public long Id { get; set; }
    public DateTime Date { get; set; }
    public DbGeography Location { get; set; }
}

在 class DatabaseHelper 我尝试从服务器加载数据。

public async Task<IEnumerable<Event>> GetEventsAsync()
{
    var uri = new Uri(string.Format(Constants.EventsUrl, string.Empty));
    var content = await _client.GetStringAsync(uri);
    IEnumerable<Event> events = JsonConvert.DeserializeObject<List<Event>>(content);

    return events;
}

但是抛出一个错误：

Newtonsoft.Json.JsonSerializationException: Error getting value from 'WellKnownValue' on 'System.Data.Entity.Spatial.DbGeography'.

我确实发现我应该使用自定义 JsonConverter。

// DbGeographyConverter.cs

public class DbGeographyConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType.IsAssignableFrom(typeof(string));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JObject location = JObject.Load(reader);
        JToken token = location["Geography"]["WellKnownText"];
        string value = token.ToString();

        System.Data.Entity.Spatial.DbGeography converted = System.Data.Entity.Spatial.DbGeography.PointFromText(value, 4326);
        return converted;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        // Base serialization is fine 
        serializer.Serialize(writer, value);
    }
}

但是在调用http://localhost:57609/api/events，其中returns个Event对象列表时，抛出如下错误：

{"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 while copying content to a stream.","ExceptionType":"System.Net.Http.HttpRequestException","StackTrace":"   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()","InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Could not load file or assembly 'Newtonsoft.Json, Version=10.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)","ExceptionType":"System.IO.FileLoadException","StackTrace":"   at System.ModuleHandle.ResolveType(RuntimeModule module, Int32 typeToken, IntPtr* typeInstArgs, Int32 typeInstCount, IntPtr* methodInstArgs, Int32 methodInstCount, ObjectHandleOnStack type)
   at System.ModuleHandle.ResolveTypeHandleInternal(RuntimeModule module, Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)
   at System.Reflection.RuntimeModule.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments)
   at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly, RuntimeModule decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType& attributeType, IRuntimeMethodInfo& ctor, Boolean& ctorHasParameters, Boolean& isVarArg)
   at System.Reflection.CustomAttribute.IsCustomAttributeDefined(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, RuntimeType attributeFilterType, Int32 attributeCtorToken, Boolean mustBeInheritable)
   at System.Reflection.CustomAttribute.IsDefined(RuntimePropertyInfo property, RuntimeType caType)
   at System.Reflection.RuntimePropertyInfo.IsDefined(Type attributeType, Boolean inherit)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.GetSerializableMembers(Type objectType)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateProperties(Type type, MemberSerialization memberSerialization)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateObjectContract(Type objectType)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract(Type objectType)
   at Newtonsoft.Json.Serialization.DefaultContractResolver.ResolveContract(Type type)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.WriteStartArray(JsonWriter writer, Object values, JsonArrayContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)
   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)
   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)
   at System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)
   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)
   at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)"}}}

可能是什么问题？

Answer 1

问题是您引用的是 Newtonsoft.Json 10.0.0.0

Could not load file or assembly 'Newtonsoft.Json, Version=10.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference.

似乎版本 10.0.0.0 在 NuGet 服务器上不再可用，因此您不能在本地安装它。没有从哪里下载。尝试 update/install 现有版本。到时候可能有用。

Install-Package Newtonsoft.Json -Version 10.0.3

DbGeography 的反序列化 Entity Framework

Deserialization of DbGeography Entity Framework

asp.net

entity-framework

spatial-data