How to Determine If a Json Object Contains Only a Specific Key

How to determine if a JSON object contains only a specific key?

You can always just count the properties of a JObject using JContainer.Count. You want objects with one property, named "Name":

foreach (var category in jObject["Categories"].OfType<JObject>())
{
    var result = category.Count == 1 && category.Property("Name") != null;
}

The fact that you're using dynamic makes it a little harder to access the c# properties of your category JObject, since there might also be a JSON property named "Count". I'd suggest switching to explicitly typed objects and methods instead. Doing so will also give you compile-time error checking as well as possibly improved performance, as explained in How does having a dynamic variable affect performance?.

Sample fiddle here.

Update

Should I go for the Except(...).Any() solution, what would I need to put in the parenthesis?

According to the documentation, Enumerable.Except

Produces the set difference of two sequences.

So you could try something like:

    var result = !category.Properties()
        .Select(p => p.Name)
        .Except(new [] { "Name" })
        .Any();

However, there is a problem with this approach: using Except() does not meet your stated requirement that you need to

... determine for each category whether or not it consists of the Name key only.

Except(...).Any() will test whether there are additional keys other than Name, but it will not test for the presence of the Name key itself, since it will get filtered out. Thus an empty JSON object {} would incorrectly get accepted.

Instead, you would need to check for sequence equality, e.g. like so:

foreach (var category in jObject["Categories"].OfType<JObject>())
{
    var result = category.Properties()
        .Select(p => p.Name)
        .SequenceEqual(new [] { "Name" });
}

And if you were requiring the presence of multiple keys, since a JSON object is an unordered set of name/value pairs according to the standard, you could sort them to require an unordered sequence equality:

var requiredKeys = new [] { "Name" } // Add additional required keys here
    .OrderBy(n => n, StringComparer.Ordinal).ToArray();
foreach (var category in jObject["Categories"].OfType<JObject>())
{
    var result = category.Properties()
        .Select(p => p.Name)
        .OrderBy(n => n, StringComparer.Ordinal)
        .SequenceEqual(requiredKeys);
}

Or if you prefer you could use requiredKeys.ToHashSet(StringComparer.Ordinal) and then SetEquals().

But, in my opinion, if you just need to check whether a JSON object consists of a single specified key only, the initial solution is simplest and most declarative.

Demo fiddle #2 here.

How to check for a particular key exists in json string or not

You can parse JSON string within a Script component using JavaSerializer or JSON.Net assemblies and search for the key value.

• Importing JSON Files Using SQL Server Integration Services
• newtonsoft json package requires reinstall every time i open code

If the JSON data is formal and contains only keys and values then you can search for the following string "-1":, if it is found then the -1 key is found.

if(json.contains("\"-1\":")){

//key found

}else{

// key not found

} 

How to check if a JSON key exists?

JSONObject class has a method named "has":

http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)

Returns true if this object has a mapping for name. The mapping may be NULL.

How to check if a key exists in Json Object and get its value

Use below code to find key is exist or not in JsonObject. has("key") method is used to find keys in JsonObject.

containerObject = new JSONObject(container);
//has method
if (containerObject.has("video")) {
    //get Value of video
    String video = containerObject.optString("video");
}

If you are using optString("key") method to get String value then don't worry about keys are existing or not in the JsonObject.

How to check if a JSON Array object contains a Key

myJSONArrayObject is an array. It doesn't have 12 as a property (Unless there are 12+ items in the array)

So, check if some of the objects in the array have myIntegerKey as a property

const exists = data.myJSONArrayObject.some(o => myIntegerKey in o)

or if myIntegerKey is always an own property

const exists = data.myJSONArrayObject.some(o => o.hasOwnProperty(myIntegerKey))

Here's a snippet:

const data={myJSONArrayObject:[{"12":{}},{"22":{}}]},      myIntegerKey = 12,      exists = data.myJSONArrayObject.some(o => myIntegerKey in o);
console.log(exists)

var keys = Object.keys(text);
var key = keys[0];

if (keys.length !== 1 || key !== "id" || text[key] !== "message")
    alert("Wrong object");

$.getJSON(sSource, aoData, function (data) {
    if ('errorMessage' in data) {
        //there was an error
    }
});

  private List<String> findScales(List<String> keys_array){
        List<String> foundedScales = new ArrayList<>();
        try {
            JSONObject jsonObj = new JSONObject(loadJSONFromAsset());
            JSONArray rootElement = jsonObj.getJSONArray("allScalesJson");
            ArrayList<String> scales_found = new ArrayList<>();

            for (int i = 0; i < rootElement.length(); i++) {
                JSONObject obj = rootElement.getJSONObject(i);

                String scale = obj.getString("scale");

                // Keys is json array
                JSONArray genreArray = obj.getJSONArray("keys");
                boolean all_found = true;

                for(String key: keys_array){
                   boolean found_this_key = false;
                   for (int j = 0; j < genreArray.length(); j++) {
                      if(key.equals(genreArray.getString(j))){
                          found_this_key = true;
                          break;
                      }
                   }
                   if(!found_this_key){
                        all_found = false;
                        break;
                   }
                }

                if(all_found){
                    scales_found.add(scale);
                }
            }

            return scales_found;
        }catch (Exception e){e.printStackTrace();}


        return foundedScales;
    }