Update JSON object

Question

I am trying to read and update a JSON array from a file. But i am getting this error while trying to update the value of a property. - Property or indexer cannot be assigned to “--” it is read only

Here's my code -

var referenceFile = @"TestData\report.json";
var json1 = File.ReadAllText(referenceFile);

JArray jsonArray = JArray.Parse(json1);
JObject array = JObject.Parse(jsonArray[0].ToString());

foreach (var item in array)
{
    var x = item.Value;
    item.Value = "test"; // Error
}

My question is how can i update the JSON. this is the json file i need to update.

[
  {
    "description": "",
    "elements": [
      {
         "description": ""
            ],
    "id": "",
    "keyword": "Feature",
    "line": 1,
    "name": "Validate data via DB Connection",
    "uri": "dbtest/DB_Query.feature"
  }
]

The "elements" property is an array of object with one object but this object is never ended. A "}" is missing before the "]". Probably not related to your issue. — Arcord
– Arcord, Commented Jul 9, 2020 at 12:39

Guru Stron · Accepted Answer · 2020-07-09 12:41:21Z

With fixed json you can use Replace, for example to change all values to "test":

var json = @"[
  {
    ""description"": """",
    ""elements"": [
      {
         ""description"": """"
       }],
    ""id"": """",
    ""keyword"": ""Feature"",
    ""line"": 1,
    ""name"": ""Validate data via DB Connection"",
    ""uri"": ""dbtest/DB_Query.feature""
  }
]";

var jarr = JArray.Parse(json);
foreach(var jVal in jarr.Descendants().OfType<JValue>())
{
    jVal.Replace(new JValue("test"));
}

You will end up with next json for jarr:

[
  {
    "description": "test",
    "elements": [
      {
        "description": "test"
      }
    ],
    "id": "test",
    "keyword": "test",
    "line": "test",
    "name": "test",
    "uri": "test"
  }
]

If you want to change concrete property you can just use indexers:

jarr[0]["description"] = "test1"; // sets root "description" of first element to "test1"

Tom W · Accepted Answer · 2020-07-09 13:04:39Z

0

You are iterating a JObject - which you have called array and so the iterator type will be KeyValuePair<string, JToken>. The property KeyValuePair.Value has a getter only

I expect what you intended to do was loop over the properties of the object, so that the iterator type is JProperty. These are exposed through JObject.Properties().

edited Jul 9, 2020 at 13:04

answered Jul 9, 2020 at 12:53

Tom W

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Comments

Arcord · Accepted Answer · 2020-07-09 12:43:47Z

0

Shouldn't you create an class that represent the JSON ?

In that case you could deserialize the JSON into a object, update it and serialize it again ?

var myObject JsonConvert.DeserializeObject<MyClass>(json1);
myObject.First().Description = "Hello" // Obviously you modify the field/value you want
var json2 JsonConvert.SerializeObject(myObject);

It will improve a lot the readibility instead of using the JArray/JObject.

answered Jul 9, 2020 at 12:43

Arcord

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Comments

Amogh Sarpotdar · Accepted Answer · 2020-07-09 13:13:12Z

Answer provided by Guru Stron above should help! If you are using visual studio IDE, with your code -

foreach (var item in array)
        {
            var x = item.Value;
            item.Value = "test"; // Error
        }

the build failure occurs with clear explaination : 'Property or indexer 'KeyValuePair<string, JToken?>.Value' cannot be assigned to -- it is read only.

In short, with your code, you are trying to change something that is read only.

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