Get value from JToken that may not exist best practices

Question

What s the best practice for retrieving JSON values that may not even exist in C  using Json NET   Right now I m dealing with a JSON provider that returns JSON that sometimes contains certain key value pairs  and sometimes does not  I ve been using  perhaps incorrectly  this method to get my values  example for getting a double    if null    jToken  width        width   double Parse jToken  width   ToString     else     width   100    Now that works fine  but when there are a lot of them it s cumbersome  I ended up writing an extension method  and only after writing it did I wonder whether maybe I was being stupid    anyways  here is the extension method  I only include cases for double and string  but in reality I have quite a few more    public static T GetValue lt T gt  this JToken jToken  string key                              T defaultValue   default T         T returnValue   defaultValue       if  jToken key     null                object data   null          string sData   jToken key  ToString             Type type   typeof T            if  type is double              data   double Parse sData           else if  type is string              data   sData           if  null    data  amp  amp  type IsValueType              throw new ArgumentException  Cannot parse type                        type FullName       from value       sData                   returnValue    T Convert ChangeType data               type  CultureInfo InvariantCulture              return returnValue      And here s an example of using the extension method   width   jToken GetValue lt double gt   width   100     BTW  Please forgive what may be a really dumb question  since it seems like something there should be a built in function for    I did try Google  and Json NET documentation  however I m either inept at finding the solution to my question or it s not clear in the documentation

User · Answer

I would write GetValue as below  public static T GetValue lt T gt  this JToken jToken  string key  T defaultValue   default T         dynamic ret   jToken key       if  ret    null  return defaultValue      if  ret is JObject  return JsonConvert DeserializeObject lt T gt  ret ToString         return  T ret      This way you can get the value of not only the basic types but also complex objects  Here is a sample  public class ClassA       public int I      public double D      public ClassB ClassB    public class ClassB       public int I      public string S     var jt   JToken Parse    I 1  D 3 5  ClassB  I 2  S  test         int i1   jt GetValue lt int gt   I    double d1   jt GetValue lt double gt   D    ClassB b   jt GetValue lt ClassB gt   ClassB

User · Answer

You can simply typecast  and it will do the conversion for you  e g   var with    double   jToken key     100    It will automatically return null if said key is not present in the object  so there s no need to test for it

User · Answer

This is pretty much what the generic method Value   is for  You get exactly the behavior you want if you combine it with nullable value types and the    operator   width   jToken Value lt double  gt   width      100

User · Answer

Here is how you can check if the token exists   if  jobject  Result   SelectToken  Items      null            It checks if  Items  exists in  Result    This is a NOT working example that causes exception   if  jobject  Result    Items      null

User · Answer

TYPE variable   jsonbody  key    Value lt TYPE gt       DEFAULT VALUE   e g   bool attachMap   jsonbody  map    Value lt bool gt       false

User · Answer

This takes care of nulls  var body   JObject Parse  anyjsonString     body  SelectToken  path-string-prop    ToString     body  SelectToken  path-double-prop    ToObject lt double gt

[c#] Get value from JToken that may not exist (best practices)

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