Question

我正在按照John Papa在其最新的PluralSight课程中概述的方法，使用Angular，Breeze和Web API 2构建SPA。

一切正常，我可以提取信息，更新，插入，删除回服务器。但是我正在使用空间类型，当我尝试更新具有空间类型的实体时，我得到以下错误

发生了'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'WellKnownValue'获取值时出错       'System.Data.Entity.Spatial.DbGeometry'。

内部异常似乎指向WellKnownValue为空的事实，尽管如此，因为我检查了发送到服务器的JSON，然后将其发送到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，可以在NewtonSoft库中反序列化DbGeometry类型，如果没有，有什么建议可以解决这个问题。

Answer 1

System.Data.Spatial.DbGeometry与Newtonsoft.Json

的效果不佳

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; }

现在当你点击BreezeController时，反序列化将由我们新的DbGeometryConverter处理。

希望它有所帮助。

Answer 2

上面的答案很有效，但是对于SRID（CoordinateSystemId）2193进行了硬编码。然而，坐标系统ID可以存在于问题中所示的序列化数据中，或者它可以存在于WellKnownText＆＃34; SRID = 2193; POINT（0 0）＆＃34;中。此方法也只会读取多边形，但WellKnownText可以是很多东西，如Geometry Collections，Point，Linestring等。要进行检索，可以更新ReadJson方法以使用更通用的FromText方法，如下所示。以上是使用更通用的坐标系更新的类，也适用于任何几何类型。我还添加了地理版本作为参考。

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);
    }
}

Answer 3

我不明白为什么不。与（DbGeometryWellKnownValue）一致：

"$type": "System.Data.Entity.Spatial.DbGeometryWellKnownValue, EntityFramework",

应该是（DbGeometry.WellKnownValue）吗？

  "$type": "System.Data.Entity.Spatial.DbGeometry.WellKnownValue, EntityFramework",

使用Newtonsoft.Json反序列化DbGeometry

3 个答案: