当属性名称变化时，LINQ和JSON.NET

Question

我试图将一些JSON内容解析为C＃。对于更简单的情况，我在JSON.NET上取得了巨大的成功，并且非常感谢LINQ提供商提供的干净方法。这是一个例子，我在地图中下载有关图层的信息，并在一个叫做的类上填充一些属性（令人惊讶！）图层：

        using (var client = new WebClient())
        {
            _content = client.DownloadString(_url.AbsoluteUri + OutputFormats.Json);
        }

        JObject json = JObject.Parse(_content);
        IEnumerable<Field> fields = from f in json["fields"].Children()
                                    select new Field(
                                        (string)f["name"],
                                        (string)f["alias"],
                                        (EsriFieldType)Enum.Parse(typeof(EsriFieldType), (string)f["type"])
                                        );
        _fields = fields.ToList();
        _displayFieldName = (string)json["displayField"];

您可以查看此网址，了解该方法的JSON详情： http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/WaterTemplate/WaterDistributionNetwork/MapServer/1?f=json&pretty=true 。但是当我需要将与地图图层关联的单个数据字段转换为DataTable甚至只是字典结构时，问题就出现了。问题是，与RSS提要或其他一致格式不同，字段名称和字段数量从地图图层更改为地图图层。以下是我运行查询的示例：

    [Test]
    [Category(Online)]
    public void Can_query_a_single_feature_by_id()
    {
        var layer = _map.LayersWithName(ObjectMother.LayerWithoutOID)[0];
        layer.FindFeatureById("13141");
        Assert.IsNotNull(layer.QueryResults);
    }

在layer.FindFeatureById中运行的代码是这个，包括我卡住的部分：

        public void FindFeatureById(string id)
    {
        var queryThis = ObjectIdField() ?? DisplayField();
        var queryUrl = string.Format("/query{0}&outFields=*&where=", OutputFormats.Json);
        var whereClause = queryThis.DataType == typeof(string)
                                 ? string.Format("{0}='{1}'", queryThis.Name, id)
                                 : string.Format("{0}={1}", queryThis.Name, id);
        var where = queryUrl + HttpUtility.UrlEncode(whereClause);
        var url = new Uri(_url.AbsoluteUri + where);
        Debug.WriteLine(url.AbsoluteUri);
        string result;

        using (var client = new WebClient())
        {
            result = client.DownloadString(url);
        }

        JObject json = JObject.Parse(result);
        IEnumerable<string> fields = from r in json["fieldAliases"].Children()
                                     select ((JProperty)r).Name;
        // Erm...not sure how to get this done.
        // Basically need to populate class instances/rows with the 
        // values for each field where the list of fields is not
        // known beforehand.

    }

您可以通过访问此URL看到JSON吐出（请注意切割'n'paste时的编码）：href =＆quot; http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/WaterTemplate/WaterDistributionNetwork /地图服务器/ 1 /查询F = JSON＆安培;外场= *＆安培;其中= FACILITYID％3d'13141'

所以我的问题（最后！）就是这样。如何循环收集“属性”？在“特征”中获取实际的字段值。你可以看到我已经弄清楚如何从fieldAliases中获取字段名称，但之后我很难过。我一直在修补一个看起来像这样的文件的JsonReader，但仍然没有快乐：

{
  "displayFieldName" : "FACILITYID", 
  "fieldAliases" : {
  "FACILITYID" : "Facility Identifier", 
  "ACCOUNTID" : "Account Identifier", 
  "LOCATIONID" : "Location Identifier", 
  "CRITICAL" : "Critical Customer", 
  "ENABLED" : "Enabled", 
  "ACTIVEFLAG" : "Active Flag", 
  "OWNEDBY" : "Owned By", 
  "MAINTBY" : "Managed By"
}, 
"features" : [
  {
    "attributes" : {
      "FACILITYID" : "3689", 
      "ACCOUNTID" : "12425", 
      "LOCATIONID" : "12425", 
      "CRITICAL" : 1, 
      "ENABLED" : 1, 
      "ACTIVEFLAG" : 1, 
      "OWNEDBY" : 1, 
      "MAINTBY" : 1
    }
  }, 
  {
    "attributes" : {
      "FACILITYID" : "4222", 
      "ACCOUNTID" : "12958", 
      "LOCATIONID" : "12958", 
      "CRITICAL" : 1, 
      "ENABLED" : 1, 
      "ACTIVEFLAG" : 1, 
      "OWNEDBY" : 1, 
      "MAINTBY" : 1
    }
  }
]
}

Answer 1

事实证明，最好的方法是使用JsonTextReader并只是翻阅数据而不是尝试使用LINQ。它有很多缩进让我感到不快，但我想这首先是使用分层数据结构的直接影响。以下是打印行列表（“属性”）及其名称/值集合的方法：

        using (var file = File.OpenText(_fileWithGeom))
        {
            JsonReader reader = new JsonTextReader(file);

            while (reader.Read())
            {
                while (Convert.ToString(reader.Value) != "features")
                {
                    reader.Read();
                }

                Console.WriteLine("Found feature collections");

                // ignore stuff until we get to attribute array

                while (reader.Read())
                {
                    switch (Convert.ToString(reader.Value))
                    {
                        case "attributes":
                            Console.WriteLine("Found feature");
                            reader.Read(); // get pass attributes property

                            do
                            {
                                // As long as we're still in the attribute list...
                                if (reader.TokenType == JsonToken.PropertyName)
                                {
                                    var fieldName = Convert.ToString(reader.Value);
                                    reader.Read();
                                    Console.WriteLine("Name: {0}  Value: {1}", fieldName, reader.Value);
                                }

                                reader.Read();

                            } while (reader.TokenType != JsonToken.EndObject
                                     && Convert.ToString(reader.Value) != "attributes");
                            break;

                        case "geometry":
                            Console.WriteLine("Found geometry");
                            reader.Read();
                            break;
                    }
                }
            }
        }

这次我还要处理几何，所以请查看以下代码解析的JSON的URL：

http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/WaterTemplate/WaterDistributionNetwork/MapServer/7/query?where=OBJECTID%3C10&returnGeometry=true&outSR=&outFields= *放大器; F = pjson

Answer 2

要获得快速而脏的（非LINQ）方法来获取属性和值，请尝试以下操作：

JObject jo = JObject.Parse(json);

foreach (JObject j in jo["features"])
{
  foreach (JProperty k in j["attributes"])
  {
    Console.WriteLine(k.Name + " = " + k.Value);
  }
}

这并不理想，但是当你不知道将要回来的字段名称时，它会起作用。如果我找到更好的方法，我会更新它。