JSON object- how to iterate through all properties without knowing their names? - json

Question

I have a fairly simple JSON:
[
{
"hero-img": "girl-ipad.png",
"main-story-headline": "How to Stay Mentally Healthy During a Pandemic",
"main-story-paragraph": "lorem ipsum",
"main-story-button-text": "Read More"
},
{
"hero-img": "painter-woman.png",
"main-story-headline": "How to Stay Mentally Healthy During a Pandemic",
"main-story-paragraph": "lorem ipsum",
"main-story-button-text": "Explore More"
},
{
"hero-img": "old-man.png",
"main-story-headline": "How to Stay Mentally Healthy During a Pandemic",
"main-story-paragraph": "lorem ipsum",
"main-story-button-text": "Get Yours Now"
} ]
By using Delphi 10.3 Rio, I want to iterate through all properties no matter how they are named. I've started this way:
program JuTemplates;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils, System.JSON, System.IOUtils, System.Types;
var
root, OutputDir, TemplatesDir, JsonDir, jsonText: string;
JsonFiles: TStringDynArray;
i, j: Integer;
JSONValue: TJSONObject;
JSONValues: TJSONArray;
begin
try
try
root := ExtractFilePath(ParamStr(0));
OutputDir := root + 'OutputDir\';
TemplatesDir := root + 'TemplatesDir\';
JsonDir := root + 'JsonDir\';
writeln('Processing: ' + JsonDir);
JsonFiles := TDirectory.GetFiles(JsonDir);
for i := 0 to High(JsonFiles) do
begin
jsonText := TFILE.ReadAllText(JsonFiles[i]);
JSONValues := TJSONObject.ParseJSONValue(jsonText) as TJSONArray;
for j := 0 to JSONValues.Count - 1 do
begin
JSONValue := JSONValues.Items[i] as TJSONObject;
// here I should iterate through that JSONValue object
end;
end;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
finally
writeln ('Press any key to continue');
readln;
end;
end.

Answer 1

To enumerate a JSONObject, you can use an enumerator like below.
Use for..in loop (implicit enumerator)
procedure TForm1.Button1Click(Sender: TObject);
var
JSONData : String;
JSONObject : TJSONObject;
JSONPair : TJSONPair;
begin
JSONData := '... some JSON data ...'; // Place you data here
JSONObject := TJSonObject.ParseJSONValue(JSONData) as TJSONObject;
try
for JSONPair in JSONObject do
ShowMessage(Format('1) Key=%s Value=%s',
[JSONPair.JsonString.ToString,
JSONPair.JsonValue.ToString]));
finally
JSONObject.Free;
end;
end;
Use a classic for loop:
procedure TForm1.Button1Click(Sender: TObject);
var
JSONData : String;
JSONObject : TJSONObject;
JSONPair : TJSONPair;
I : Integer;
begin
JSONData := '... some JSON data ...'; // Place you data here
JSONObject := TJSonObject.ParseJSONValue(JSONData) as TJSONObject;
try
for I := 0 to JSONObject.Count - 1 do begin
ShowMessage(Format('Key=%s Value=%s',
[JSONObject.Pairs[I].JsonString.ToString,
JSONObject.Pairs[I].JsonValue.ToString]));
end;
finally
JSONObject.Free;
end;
end;
Use an explicit enumerator and a while loop:
procedure TForm1.Button1Click(Sender: TObject);
var
JSONData : String;
JSONObject : TJSONObject;
JSONEnumerator : TJSONObject.TEnumerator;
JSONPair : TJSONPair;
begin
JSONData := '... some JSON data ...'; // Place you data here
JSONObject := TJSonObject.ParseJSONValue(JSONData) as TJSONObject;
try
JSONEnumerator := JSONObject.GetEnumerator;
try
while JSONEnumerator.MoveNext do begin
JSONPair := JSONEnumerator.Current;
ShowMessage(Format('Key=%s Value=%s',
[JSONPair.JsonString.ToString,
JSONPair.JsonValue.ToString]));
end;
finally
JSONEnumerator.Free;
end;
finally
JSONObject.Free;
end;
end;
Note that you may need to check if JSONPair.JsonValue has childs and enumerate those childs with another enumerator, recursively.