c# - 在 JArray 中使用 LINQ

Question

我有一个 JSON

{
  "departments": [
    {
      "2": {"city": "Petersburg", "employees": "1200"}
    },
    {
      "1": {"city": "Ekaterinburg", "employees": "4000"}
    }
  ]
}

如果我知道使用 LINQ 或其他东西的 ID，我如何获得城市的值(value)？
我试过

var id = 2;
json["departments"].Single(x=>x.Name==id.ToString())["city"];

但它不起作用，我收到一个编译错误:

'JToken' does not contain a definition for 'Name' and no accessible extension method 'Name' accepting a first argument of type 'JToken' could be found (are you missing a using directive or an assembly reference?)

演示 fiddle here .

Answer 1

您的 LINQ 查询可以按如下方式实现:

var id = "2";
var city = (string)json["departments"]
    .Where(o => o[id] != null) // From the departments array, select the object where the required id property exists
    .Select(o => o[id]["city"]).SingleOrDefault(); // An extract the value of "city" from the nested object.

或者，等效地:

var id = "2";
var city = (string)json["departments"]
    .SelectMany(i => i) // Use SelectMany() to project the properties of the array items to a flat enumerable 
    .Cast<JProperty>()  // Cast them to JProperty
    .Where(p => p.Name == id) // Now you can use Name
    .Select(p => p.Value["city"])
    .SingleOrDefault();

或者，您可以使用 SelectToken() 以此目的:

var id = "2";
var path = $"departments[*].{id}.city"; // departments[*].2.city
var city = (string)json.SelectToken(path);

SelectToken()支持 JSONPath syntax , 和 [*]是 JSONPath 通配符运算符，指示应搜索所有数组项。
演示 fiddle here .