Writing Float values to JSON

[mirce.vladimirov]

I am doind something wrong but i cant find out what it is.

This code :

Code: Pascal  [Select][+][-]

1.     while not qry1.EOF do begin
2.       jsonItem := TJSONObject.Create;
3.       jsonItem.Add('LineNo', qry1.FieldByName('line').AsInteger);
4.       jsonItem.Add('Qty',  qry1.FieldByName('qty').AsFloat);
5.       jsonItem.Add('Price', qry1.FieldByName('price').AsFloat);
6.       jsonItems.Add(jsonItem);
7.       qry1.Next;
8.     end;
9.     jsonDoc.Add('Items', jsonItems);

   
Gives me scientific notations, which i do not want, my data are float numbers with max 4 decimal places and i want them to be exported to json as such.

And when i call it as a string it encloses it in double quotes, as it should because i called it as a string :

Code: Pascal  [Select][+][-]

1. jsonItem.Add('Price', qry1.FieldByName('price').asstring);

i just want it exported as

Code: Pascal  [Select][+][-]

1. {"Price": 123.01}

and not as

Code: Pascal  [Select][+][-]

1. {"Price":"123.01"}

[Khrys]

That's just the default stringification behavior of  TJSONFloatNumber.
You can customize it by creating a subclass of  TJSONData  with the desired behavior and then registering it using  SetJSONInstanceType.

I've been using a variation of the following for a while now:

Code: Pascal  [Select][+][-]

1. const
2.   JSON_NUMBER_FORMAT: TFormatSettings = ({via initialization});
3.  
4. type
5.   TJSONDecimalNumber = class(TJSONFloatNumber)
6.   protected
7.     function GetAsString(): TJSONStringType; override;
8.   end;
9.  
10. function TJSONDecimalNumber.GetAsString(): TJSONStringType;
11. begin
12.   Result := FormatFloat('0.0###', GetAsFloat(), JSON_NUMBER_FORMAT);
13. end;
14.  
15. initialization
16. begin
17.   JSON_NUMBER_FORMAT := DefaultFormatSettings;
18.   JSON_NUMBER_FORMAT.DecimalSeparator := '.';
19.   SetJSONInstanceType(jitNumberFloat, TJSONDecimalNumber);
20. end;

[Thaddy]

In trunk, you could also use a custom attribute for that, where the attribute code handles how to format the float values.
If you want I can write an example for that (if you use trunk!).
I have recently added a code example to the custom attributes wiki entry that manipulates json:
https://wiki.freepascal.org/Custom_Attributes#Complete_example_2

In this case, you want to divert from the standard json handling of floats and that is a particularly good case for using a - maybe even parameterized - custom attribute.
You can integrate Khrys's code for that almost ad verbatum.
[edit]
I will do that anyway, but given some time.