反序列化JSON时，值不能为null

Question

I have a db table which has column in which content is stored in JSON format, I am retrieving JSON but I am getting this error.
Value cannot be null
Here is my code snippet.

var stuff = (JObject)JsonConvert.DeserializeObject(commentId);

string name = stuff["Name"].Value<string>();
string email = stuff["Email"].Value<string>();
string company = stuff["Company"].Value<string>();
string phone = stuff["Phone"].Value<string>();
string message = stuff["Message"].Value<string>();
string emails = stuff["Emails"].Value<string>();

My sample JSON:

{
  "2": {
    "label": "",
    "value": "",
    "type": null,
    "validation": null,
    "required": null,
    "min": null,
    "max": null,
    "tooltip": null,
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "3": {
    "label": "location",
    "value": "http://someurl.com/",
    "type": "hidden",
    "validation": "",
    "required": "0",
    "min": "0",
    "max": "1000",
    "tooltip": "",
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "4": {
    "label": "Name*",
    "value": "Farrukh",
    "type": "text",
    "validation": "alphabets",
    "required": "1",
    "min": "0",
    "max": "300",
    "tooltip": "field0",
    "custom": "",
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "5": {
    "label": "Email*",
    "value": "abc@a.com",
    "type": "email",
    "validation": "email",
    "required": "1",
    "min": "",
    "max": "",
    "tooltip": "field1",
    "custom": "autoreply",
    "custom2": "replyto",
    "custom3": "zz",
    "custom4": "",
    "custom5": ""
  },
  "6": {
    "label": "Company",
    "value": "Abc",
    "type": "text",
    "validation": "",
    "required": "1",
    "min": "0",
    "max": "300",
    "tooltip": "field2",
    "custom": "",
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "7": {
    "label": "Phone",
    "value": "0000000000",
    "type": "text",
    "validation": "integers",
    "required": "0",
    "min": "0",
    "max": "300",
    "tooltip": "field3",
    "custom": "",
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "8": {
    "label": "Country",
    "value": "Some country",
    "type": "dropdown",
    "validation": "",
    "required": "1",
    "min": "",
    "max": "",
    "tooltip": "field4",
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "9": {
    "label": "Message*",
    "value": "hello",
    "type": "para",
    "validation": "",
    "required": "1",
    "min": "0",
    "max": "3000",
    "tooltip": "field5",
    "custom": "",
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "10": {
    "label": "name",
    "value": "",
    "type": null,
    "validation": null,
    "required": null,
    "min": null,
    "max": null,
    "tooltip": null,
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "11": {
    "label": "title",
    "value": "",
    "type": null,
    "validation": null,
    "required": null,
    "min": null,
    "max": null,
    "tooltip": null,
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "12": {
    "label": "emails",
    "value": ",a@a.com,b@b.com,c@c.com,d@d.com",
    "type": null,
    "validation": null,
    "required": null,
    "min": null,
    "max": null,
    "tooltip": null,
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "13": {
    "label": "multi",
    "value": "true",
    "type": null,
    "validation": null,
    "required": null,
    "min": null,
    "max": null,
    "tooltip": null,
    "custom": null,
    "custom2": null,
    "custom3": "zz",
    "custom4": null,
    "custom5": null
  },
  "0": {
    "custom3": "zz",
    "value": "",
    "label": ""
  },
  "1": {
    "custom3": "zz",
    "value": "",
    "label": ""
  }
}

Answer 1

My guess is that when you do

string name = stuff["Name"].Value<string>();

and the others you are getting the value for stuff["Name"] and if it doesn't have that property in the JSON, for this example it doesn't have "Name" it will throw you "Value cannot be null"

So you need first to check if you have the values or not.

You can check like that

//check if property exists
if (stuff["Name"].Value<string>()!= null) {
    string name = stuff["Name"].Value<string>();
} else {
    //there is no "name" property, compensate somehow.
}

Answer 2

Assuming your full JSON is as you show, your JSON doesn't give simple name/value pairs for name and email. Instead it has a dictionary of indexed property objects, where each object has a label property with value equal to the name of property you seek, and an adjacent value property with the corresponding value.

You can conveniently fetch these from your JSON by building an ancillary lookup table as follows:

        var dict = JObject.Parse(commentId)
            .Descendants()
            .OfType<JProperty>()
            .Where(p => p.Name == "label")
            .ToLookup(p => (string)p.Value, p => (string)p.Parent["value"]); // Use ToLookup because some empty space keys are duplicated
        var name = dict["Name*"].SingleOrDefault(); // Notice the asterisk in the property labels.
        var email = dict["Email*"].SingleOrDefault();

And, to test:

        Debug.Assert(name == "Farrukh"); // No assert.
        Debug.Assert(email == "abc@a.com"); // No assert.

Answer 3

Pretty old topic, but I am using:

string name = stuff["Name"]?.Value<string>() ?? "undefined"; string email = stuff["Email"]?.Value<string>() ?? "undefined";

Concise and simple and also provides your own default value.