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#.
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();
If the property does not exist, the Property
method returns null, according to the documentation .
So do not call .ToString()
, otherwise you will get a NullReferenceException
. Instead:
List<JObject> newStudents = students.Where(x => x.Property("parent_id") == null).ToList();
You should do as follows
List<JObject> newStudents = students.Where(x => x.Property("parent_id").Value<string>() == null).ToList();
List<JObject> existedStudents = students.Where(x => x.Property("parent_id").Value<string>() != null).ToList();
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