Display string data in message box

Question

Why is this not working with TJSONObject?

procedure TForm1.Button5Click(Sender: TObject);
var
  js : TJSONObject;
  isoDate1, isoDate2, data : string;
begin
  isoDate1 := '2018-01-02T10:00:00.000Z';
  isoDate2 := '2018-01-02T10:10:00.000Z';

  js := TJSONObject.Create;
  js.AddPair(TJsonPair.Create(isoDate1, 'TEST'));
  js.AddPair(TJsonPair.Create(isoDate2, 'TEST2'));

  outputdebugstring(pchar(js.ToString));

  if js.TryGetValue<string>(isoDate1, data) then begin
    ShowMessage(data);
  end else begin
    ShowMessage('data non trouvé pour ' + isoDate1);
  end;
end;

output : Sortie de débogage: {"2018-01-02T10:00:00.000Z":"TEST","2018-01-02T10:10:00.000Z":"TEST2"} Processus Project1.exe (6232)

Expected Outcome:
The TryGetValue should put a string in data
ShowMessage should give me 'TEST' in a message box.

Outcome:
The ShowMessage give me 'data non trouvé pour 2018-01-02T10:00:00.000Z'.

The TryGetValue should put a string in data and ShowMessage should give me 'TEST' in a message box? — supermyz
– supermyz, Commented Feb 2, 2018 at 15:08
The ShowMessage give me 'data non trouvé pour 2018-01-02T10:00:00.000Z' which I thought definitely should be 'TEST' — supermyz
– supermyz, Commented Feb 2, 2018 at 15:17

Victoria · Accepted Answer · 2018-02-03 05:28:08Z

2

Problem is the dot in your JSON path that you query with the TryGetValue method call. Dot char path parser (TJSONPathParser) interprets as key separator of pairs, whose value is about to be obtained. So, for example call like this:

if JSONObject.TryGetValue<string>('Foo.Bar', S) then
  DoSomething;

is a query for The value of an object like this:

{"Foo": {"Bar": "The value"}}

not for The value with the key named this way:

{"Foo.Bar": "The value"}

So in your case you were trying to query the value of the 2018-01-02T10:00:00 object's key 000Z, which would require object like this:

{"2018-01-02T10:00:00": {"000Z": "TEST"}}

This JSON path dot notation is hardcoded at this time (without possibility of escaping dot chars in the queried path), so the only way is giving up on that method at this moment, or losing dots from key names.

edited Feb 3, 2018 at 5:28

answered Feb 2, 2018 at 16:07

Victoria

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3 Comments

supermyz Over a year ago

But why js.toString give me : {"2018-01-02T10:00:00.000Z":"TEST","2018-01-02T10:10:00.000Z":"TEST2"}, which is a validated JSON, also the dot is a part of ISO, I am not sure to remove it

supermyz Over a year ago

Oddly, js.GetValue(isoDate1).toString worked but not js.GetValue<string>(isoDate1)

Victoria Over a year ago

You have a valid JSON. The probem is that TryGetValue supports dot notation of paths and thinks that you're querying value of an object that I've shown in this post.

Philipp H. · Accepted Answer · 2018-02-02 16:11:08Z

2

The problem is the dot in your key. It's used as a seperator. Delphi interprets '2018-01-02T10:00:00' as an object which has '000Z' as a property.

I would sugguest to get the value like this:

var
...
  LJsonValue: TJSONValue;
begin
...

  LJsonValue := js.GetValue(isoDate1);
  if Assigned(LJsonValue) then
    ShowMessage(LJsonValue.Value);

...
end;

answered Feb 2, 2018 at 16:11

Philipp H.

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Comments

Jan Bird · Accepted Answer · 2022-08-04 08:18:27Z

0

You can use JSON path syntax in GetValue...

... MySt := JSONObject.GetValue<string>('["Foo"]["Bar"]') ...

answered Aug 4, 2022 at 8:18

Jan Bird

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