C# 使用Newtonsoft.Json反序列化DbGeometry

我正在使用Angular、Breeze和WebAPI2构建一个水疗中心，遵循John Papa在其最新PluralSight课程中概述的方法

一切都很好，我可以拉信息，更新，插入，删除回服务器。然而，我使用的是空间类型，当我尝试用空间类型更新实体时，我得到以下错误

在中发生“Newtonsoft.Json.JsonSerializationException”类型的异常 Newtonsoft.Json.dll，但未在用户代码中处理

其他信息：从上的“WellKnownValue”获取值时出错 “System.Data.Entity.Spatial.DbGeometry”

内部异常似乎指向WellKnownValue为null这一事实，但事实并非如此，因为我已经检查了发送到服务器的JSON，该JSON随后被发送到Breeze ContextProvider并使用SaveChanges方法保存

{
"entities": [
 {
  "TableKey": 2,
  "CaseName": "Mikhail Lermontov",
  "StartDate": "2013-06-11T00:00:00Z",
  "EndDate": null,
  "IsCurrent": true,
  "SRID": 109,
  "Shape": {
    "$id": "2",
    "$type": "System.Data.Entity.Spatial.DbGeometry, EntityFramework",
    "Geometry": {
      "$id": "3",
      "$type": "System.Data.Entity.Spatial.DbGeometryWellKnownValue, EntityFramework",
      "CoordinateSystemId": 2193,
      "WellKnownText": "POLYGON ((1695943 5462665, 1713098 5462665, 1713098 5449659, 1695943 5449659, 1695943 5462665))"
    }
  },
  "SpillLocation": "Marlborough Sounds",
  "Image": "http://www.nzmaritime.co.nz/images/lm5.jpg\r\n",
  "DefaultBaseMapKey": 2,
  "__unmapped": {
    "isPartial": false
  },
  "entityAspect": {
    "entityTypeName": "DatSpillCase:#Osiris.Model",
    "defaultResourceName": "DatSpillCases",
    "entityState": "Modified",
    "originalValuesMap": {
      "CaseName": "Mikhail Lermontov"
    },
    "autoGeneratedKey": {
      "propertyName": "TableKey",
      "autoGeneratedKeyType": "Identity"
    }
  }
}
 ],
  "saveOptions": {}
}

---

所以我的问题是，是否可以在NewtonSoft库中反序列化DbGeometry类型，如果不可以，有什么建议可以解决这个问题。

我不明白为什么不可以。在具有（DbGeometryWellKnownValue）的行上：

这应该是（DbGeometry.WellKnownValue）吗

---

System.Data.Spatial.DbGeometry

与

Newtonsoft.Json

您需要创建一个

JsonConverter

来转换

DbGeometry

public class DbGeometryConverter : 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["Geometry"]["WellKnownText"];
            string value = token.ToString();

            DbGeometry converted = DbGeometry.PolygonFromText(value, 2193);
            return converted;
        }

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

然后在模型中的属性上添加属性

[JsonConverter(typeof(DbGeometryConverter))]
public DbGeometry Shape { get; set; }

现在，当您点击BreezeController时，反序列化将由新的DbGeometryConverter处理

---

希望能有所帮助。

上面的答案非常有效，但它是为SRID（CoordinationSystemID）2193硬编码的。 但是，坐标系Id可以出现在问题所示的序列化数据中，也可以出现在WellKnownText“SRID=2193；点（0）”中。此外，此方法将仅读取多边形，但WellKnownText可以是许多内容，如几何体集合、点、线字符串等。要检索此内容，可以更新ReadJson方法，以使用更通用的FromText方法，如下所示。 下面是使用更通用的坐标系更新的上面的类，也适用于任何几何体类型。我还添加了地理版本以供参考

public class DbGeometryConverter : 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["Geometry"]["WellKnownText"];
        string value = token.ToString();
        JToken sridToken = location["Geometry"]["CoordinateSystemId"];
        int srid;
        if (sridToken == null || int.TryParse(sridToken.ToString(), out srid) == false || value.Contains("SRID"))
        {
            //Set default coordinate system here.
            srid = 0;
        }

        DbGeometry converted;
        if (srid > 0)
            converted = DbGeometry.FromText(value, srid);
        else
            converted = DbGeometry.FromText(value);
        return converted;
    }

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

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["Geometry"]["WellKnownText"];
        string value = token.ToString();
        JToken sridToken = location["Geometry"]["CoordinateSystemId"];
        int srid;
        if (sridToken == null || int.TryParse(sridToken.ToString(), out srid) == false || value.Contains("SRID"))
        {
            //Set default coordinate system here.
            //NOTE: Geography should always have an SRID, and it has to match the data in the database else all comparisons will return NULL!
            srid = 0;
        }
        DbGeography converted;
        if (srid > 0)
            converted = DbGeography.FromText(value, srid);
        else
            converted = DbGeography.FromText(value);
        return converted;
    }

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

---

我用来序列化和反序列化地理类型变量的是GeoJSON。在这个地址已经有一个未完成的.Net库，尽管仍然缺少一些东西。您可以随时从该项目编写自己的序列化程序/反序列化程序。这种方法也适用于

DbGeography

，您只需将

location[“Geometry”][“WellKnownText”]

更改为

location[“Geography”][“WellKnownText”]

和

DbGeometry converted=DbGeometry.PolygonFromText（值，2193）；

到

var converted=DbGeography.FromText（值）；

我认为对于DbGeographyConverter，您需要使用“Geography”字符串而不是“Geometry”来标记和sridToken。

[JsonConverter(typeof(DbGeometryConverter))]
public DbGeometry Shape { get; set; }

public class DbGeometryConverter : 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["Geometry"]["WellKnownText"];
        string value = token.ToString();
        JToken sridToken = location["Geometry"]["CoordinateSystemId"];
        int srid;
        if (sridToken == null || int.TryParse(sridToken.ToString(), out srid) == false || value.Contains("SRID"))
        {
            //Set default coordinate system here.
            srid = 0;
        }

        DbGeometry converted;
        if (srid > 0)
            converted = DbGeometry.FromText(value, srid);
        else
            converted = DbGeometry.FromText(value);
        return converted;
    }

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

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["Geometry"]["WellKnownText"];
        string value = token.ToString();
        JToken sridToken = location["Geometry"]["CoordinateSystemId"];
        int srid;
        if (sridToken == null || int.TryParse(sridToken.ToString(), out srid) == false || value.Contains("SRID"))
        {
            //Set default coordinate system here.
            //NOTE: Geography should always have an SRID, and it has to match the data in the database else all comparisons will return NULL!
            srid = 0;
        }
        DbGeography converted;
        if (srid > 0)
            converted = DbGeography.FromText(value, srid);
        else
            converted = DbGeography.FromText(value);
        return converted;
    }

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