C# 使用 Newtonsoft 部分解析/反序列化 JSON

Question

I have to extract a part of json-string using .net or newtonsoft json.

JSON:

var json = "{\"method\":\"subtract\",\"parameters\":{\"minuend\":\"SOME_CUSTOM_JSON_OBJECT_DIFFERENT_FOR_EACH_METHOD\",\"subtrahend\":23}}";

C# Class:

class MyJson{
    public string method { get; set; }
    //public string parameters {get; set;}
    public object parameters {get; set;}
}

1. I do not need to parse all the children of "parameters" json-object. "parameters" could be a very big object ([{obj1}...{obj1000}], objX of 1000 fields), parse which would be not performant. I would like ie to pass it exactly as it is on some point, so conversion "string-C#object-string" would be redundant.
2. I do not want use Regexp or string transformations (string.Substring, Split and co), because of error margin, I know that all .net and newtonsoft string transformations based.

Question 1: if I define a property of type "object", how newtonsoft will handle this? (Documentation is worse than msdn, so I'm looking for the input from you, who already tried this).

static void Main(string[] args)
{
     var json = "{\"method\":\"subtract\",\"parameters\":{\"minuend\":42,\"subtrahend\":23}}";
     var data = JsonConvert.DeserializeObject<MyJson>(j);

     // what internal representaion of data.parameters?
     // How is it actually converted from json-string to an C# object (JObject/JsonObject).
}

In perfect case: "parameters" is a string and calling

ExtractMyJson(jsonString)

gives me the json string of parameters.

Basically I need the newtonsoft version of

string ExtractMyJson(jsonString){
  var p1 = jsonString.Split(",");
  // .. varios string transformations
  return pParams;
}

Note: please don't reference "dynamic" keyword or ask why no string transformations, it's the very specific question.

Answer 1

If you know that your parameters are unique you can do something like this:

class MyJson
{
    public string method { get; set; }
    public Dictionary<string,object> parameters { get; set; }
}
................
string json = "{\"method\":\"subtract\",\"parameters\":{\"minuend\":{\"img\": 3, \"real\": 4},\"subtrahend\":23}}";
var data = JsonConvert.DeserializeObject<MyJson>(json);

If you let it as object is going to receive the type Newtonsoft.Json.Linq.JObject.

Answer 2

Well Objects are treated the same way your parent object is treated. It will start from the base of the graph. So if you have something like:

Person
{
 Address Address {get;set;}
}

The Json will start Deserializing Address and then add in the Person object. If you want to limit thesize of the graph depth you can use a setting like :

JsonConvert.DeserializeObject<List<IList<IList<string>>>>(json, new JsonSerializerSettings
 {
    MaxDepth = 2
 });

For more configurations of the JsonSerializer check JsonSerializerSettings

If your field is an object then that object will have the KeyValuePair of every property that it holds, based on that when you cast that field you can access that type.(the behaviour is the same as assigning a type to an object in C#).

Update: So if you question using JsonObject or type, well JObject is and intermediary way to construct the json format in a generic format. But using the Type deserializatin means you can ignore properties you are not interested in. Mapping to a json with a type makes more sense because it creates a new object and dismisses the old JObject.

Answer 3

Have you tried JTOKEN ?

It is a rather simple solution to partially read basic or nested JSONs as described in this post .

For a nested JSON

{ 
"key1": {
            "key11": "value11",
            "key12": "value12"
         }
"key2": "value2"
}

it would look like this

JToken token = JToken.Parse(json);
var value12 = token.SelectToken("key1.key12");

to get the element of the key "key12 .

I think this could go nicely with your problem.