How can I parse a nested TJSONObject in Delphi?

Question

My Delphi application calls a REST API, which produces the following JSON:

{
   "status": "success",
   "message": "More details",
   "data": {
      "filestring": "long string with data",
      "correct": [
         {
            "record": "Lorem ipsum",
            "code": 0,
            "errors": []
         }
      ],
      "incorrect": [
         {
            "record": "Lorem ipsum",
            "code": 2,
            "errors": [
               "First error",
               "Second error"
            ]
         }
      ],
   }
}

I now want to work with the data, but I am unable to receive the information stored in the data section. Currently I am trying to receive the data like below:

var
   vResponse : TJSONObject;
   vData : TJSONObject;
begin
   // .. do other stuff ..
   vResponse := // call to REST API (Returns a valid TJSONObject I've wrote it into a file)
   vData := vResponse.get('data'); // throws error
end;

But this leads to the following error:

Incompatible Types: TJSONObject and TJSONPair

Does anybody know how I can achieve this?

Remy Lebeau · Accepted Answer · 2022-02-17 22:25:44Z

2

TJSONObject.Get() returns a TJSONPair, not a TJSONObject. You will have to either:

use the TJSONPair.JsonValue property:

var
  vResponse : TJSONObject;
 vData : TJSONObject;
begin
  // .. do other stuff ..
  vResponse := // call to REST API (Returns a valid TJSONObject I've wrote it into a file)
  vData := vResponse.Get('data').JsonValue as TJSONObject;
end;

use the TJSONObject.GetValue() method, which returns just the JsonValue of the found TJSONPair:

var
  vResponse : TJSONObject;
  vData : TJSONObject;
begin
  // .. do other stuff ..
  vResponse := // call to REST API (Returns a valid TJSONObject I've wrote it into a file)
  vData := vResponse.GetValue('data') as TJSONObject;
end;

edited Feb 17, 2022 at 22:25

answered Feb 17, 2022 at 21:48

Remy Lebeau

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3 Comments

Mawg Over a year ago

That's not really getting at the nested data, is it? Or, am I missing something? I had hoped to see how to get the value of, for instance ['data']['incorrect']['code']

Remy Lebeau Over a year ago

It is just the 1st step. Repeat the step over and over for each nested value as needed. So, Get/Value the data object, then Get/Value its incorrect object, then Get/Value its code.

Mawg Over a year ago

Thank you very much, Rene. I figured out some code and posted it here in the hope that it might help others. The code could be polished, but it works.

AmigoJack · Accepted Answer · 2022-02-17 12:54:12Z

2

Incompatible Types: TJSONObject and TJSONPair

The error message is self explaining: vData is declared as TJSONObject, which means that the return type of the Get function is TJSONPair.

To fix such errors you need to change the declaration of the result variable. In this case that would mean declaring vData as TJSONPair.

However, if you are not interested in getting a pair, but instead TJSONObject, you need to use other ways to retrieve it. For instance the Values property. Because Values returns TJSONValue you need to typecast it to TJSONObject if you know that the value is an object.

vData := vResponse.Values['data'] as TJSONObject;

edited Feb 17, 2022 at 12:54

AmigoJack

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answered Feb 17, 2022 at 10:49

Dalija Prasnikar♦

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1 Comment

Max Kleiner Over a year ago

Or you get the object as property: vdata:= vresponse.values['data'].asObject; writeln(objtostr(vdata)); >>>TJsonObject2@094F3E10

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