Q:

How to get list of objects from list of jobjects based on key exists or not?

This is my code:-
List<JObject> students =[{"id":"101","name":"one","parent_id":"1"},{"id":"102","name":"two","parent_id":"2"},{"id":"103","name":"three"},{"id":"104","name":"four"}];

I tried the following code using Linq but not working
List<JObject> newStudents = students.Where(x => x.Property("parent_id").ToString() == null).ToList();

List<JObject> existedStudents = students.Where(x => x.Property("parent_id").ToString() != null).ToList();

In the above list contains 4 objects , first two objects contains parent_id key next two objects doesn't contain. How to parent_id key existed and not existed list in c#.  

A:

According to the documentation, JObject.Property returns null if the property does not exist
Thus
x.Property("parent_id").ToString()

will throw a NullReferenceException if parent_id does not exist.
To check whether a property exists do not use the ToString(), just compare Property to null:
List<JObject> newStudents = students.Where(x => x.Property("parent_id") == null).ToList();

