实体框架- JSON.netjsonconverter for DbGeography

Question

长期挣扎在这个…

基本上，我有一个具有DbGeography属性的模型优先EF5对象。我想应用一个JsonConverter，让它作为简单的纬度/经度值往返。我正在使用WebAPI。

查找JSON输出和输入如下:

{
    "location":
    {
        "geopoint":
        {
            "latitude":40.770712,
            "longitude":-73.962011
        }
    }
}

这是我的类定义和JsonConverter:

[MetadataType(typeof(QueryLocationMetadata))]
partial class Location
{
}
public class QueryLocationMetadata
{
    [JsonConverter(typeof(DbGeographyConverter))]
    public virtual DbGeography GeoPoint { get; set; }
}

public class DbGeographyConverter : JsonConverter
{
    private const string LATITUDE_KEY = "latitude";
    private const string LONGITUDE_KEY = "longitude";
    public override bool CanConvert(Type objectType)
    {
        return objectType.Equals(typeof(DbGeography));
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return default(DbGeography);
        var jObject = JObject.Load(reader);
        if (!jObject.HasValues || (jObject.Property(LATITUDE_KEY) == null || jObject.Property(LONGITUDE_KEY) == null))
            return default(DbGeography);
        string wkt = string.Format("POINT({1} {0})", jObject[LATITUDE_KEY], jObject[LONGITUDE_KEY]);
        return DbGeography.FromText(wkt, DbGeography.DefaultCoordinateSystemId);
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var dbGeography = value as DbGeography;
        serializer.Serialize(writer, dbGeography == null || dbGeography.IsEmpty ? null : new { latitude = dbGeography.Latitude.Value, longitude = dbGeography.Longitude.Value });
    }
}

所以使用这个，我能够成功地序列化甚至正确地反序列化一个对象，但在我击中ApiController动作之前，我得到了以下错误:

System.Data.SqlTypes.SqlNullValueException: Data is Null. This method or property cannot be called on Null values.
   at System.Data.SqlTypes.SqlDouble.get_Value()
   at GetValueFromSqlDouble(Object )
   at System.Web.Http.Metadata.Providers.AssociatedMetadataProvider`1.<>c__DisplayClass3.<GetMetadataForPropertiesImpl>b__0()
   at System.Web.Http.Metadata.ModelMetadata.get_Model()
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateProperties(ModelMetadata metadata, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateProperties(ModelMetadata metadata, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateProperties(ModelMetadata metadata, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateProperties(ModelMetadata metadata, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateElements(IEnumerable model, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateProperties(ModelMetadata metadata, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateElements(IEnumerable model, ValidationContext validationContext)
   at System.Web.Http.Validation.DefaultBodyModelValidator.ValidateNodeAndChildren(ModelMetadata metadata, ValidationContext validationContext, Object container)
   at System.Web.Http.Validation.DefaultBodyModelValidator.Validate(Object model, Type type, ModelMetadataProvider metadataProvider, HttpActionContext actionContext, String keyPrefix)
   at System.Web.Http.ModelBinding.FormatterParameterBinding.<>c__DisplayClass1.<ExecuteBindingAsync>b__0(Object model)
   at System.Threading.Tasks.TaskHelpersExtensions.<>c__DisplayClass36`1.<>c__DisplayClass38.<Then>b__35()
   at System.Threading.Tasks.TaskHelpersExtensions.<>c__DisplayClass49.<ToAsyncVoidTask>b__48()
   at System.Threading.Tasks.TaskHelpers.RunSynchronously[TResult](Func`1 func, CancellationToken cancellationToken)

在闲逛和谷歌各种各样的东西之后，我完全不知所措。我得到的是，它试图验证属性，但SqlDouble?

Answer 1

Youssef提到的错误已经修复，但我仍然遇到问题，在验证过程中的某个地方为DbGeography创建自定义JsonConverter时，DefaultBodyModelValidator陷入了循环。我的解决方案不是完全禁用模型验证，而是将默认验证器替换为派生的验证器，该验证器将DbGeography类型从深度验证中排除。

为了避免重复，您可以在这里看到完整的解决方案。

Answer 2

问题不在于您的转换器。这是一个已知的验证错误，发生在公共属性的getter抛出对象图时。此工作项跟踪问题:

http://aspnetwebstack.codeplex.com/workitem/740

同时，您应该能够通过禁用验证来绕过它:

config.Services.Clear(typeof(ModelValidatorProvider));

给您带来不便，敬请谅解。