How to add objects into array? (TwinCAT3)

I would like to save my array of objects (arr) into json file from Beckhoff TwinCAT3 using FB_JsonDomParser. This is what I want to get:

{ 'MyArray' : [{a: 1, b: 0.4}, {a: 3, b: 9.1}, {a: 6, b: 0.1}] }

This is my attempt, where I couldn't find anything suitable within push methods.

fbJson : FB_JsonDomParser;
jRoot : SJsonValue;
jArray : SJsonValue;
bSaveJsonFile : BOOL;
arr : ARRAY[0..9] OF MYSTRUCT; // structure contains int and real

jRoot := fbJson.NewDocument();
jArray := fbJson.AddArrayMember(jRoot, 'MyArray', 0);
// not sure how to add objects here into jArray

fbJson.SaveDocumentToFile(sFile := 'C:\tmp\test.json', bExec := bSaveJsonFile);

Not a user of json in TwinCAT, but I played around a bit and created what you are looking for, though I used FB_JsonSaxWriter and FB_JsonReadWriteDataType, let me know if this helps. This could be encapsulated as a function or a method that could be used for generics instead of using specific data type like here, but it should serve as a sufficient example imho.

Here is the code:

PROGRAM MAIN
VAR
    arr : ARRAY [0..3] OF ST_MyDataType := [
        (realVal := 0.0, intVal := 0),
        (realVal := 1.0, intVal := 1),
        (realVal := 2.0, intVal := 2),
        (realVal := 3.0, intVal := 3)];
        
    bWriteToFile    : BOOL;
    bWriteSuccess   : BOOL;
    nArrayIteration : UDINT;
    fbJsonDataType  : FB_JsonReadWriteDataType;
    fbJsonWriter    : FB_JsonSaxWriter;
    fbJson          : FB_JsonDomParser;
    sJsonDoc        : STRING(2000);
    bCreateJsonDoc  : BOOL;
END_VAR

IF bCreateJsonDoc THEN
    bCreateJsonDoc := FALSE;
    fbJsonWriter.ResetDocument();
    fbJsonWriter.StartObject();
    fbJsonWriter.AddString('My array of structures');
    // Start the array
    fbJsonWriter.StartArray();
    
    // Iterate the array's objects here
    FOR nArrayIteration := 0 TO SIZEOF(arr)/SIZEOF(ST_MyDataType) - 1 BY 1 DO
        // Create an object and the values based on the current iteration of the array
        fbJsonDataType.AddJsonValueFromSymbol(
            fbjsonwriter,
            'ST_MyDataType', 
            SIZEOF(ST_MyDataType), 
            ADR(arr) + nArrayIteration*SIZEOF(ST_MyDataType));
            
        // Object end (all struct members written)
    END_FOR
    
    // End the array and create the json doc as a string to be written
    fbJsonWriter.EndArray();
    fbJsonWriter.EndObject();
    fbJsonWriter.CopyDocument(sJsonDoc, SIZEOF(sJsonDoc));
    fbJson.ParseDocument(sJsonDoc);
END_IF

bWriteSuccess := fbJson.SaveDocumentToFile(
    bExec := bWriteToFile, 
    sFile := 'C:\JsonTest\Test.json');

Here is the resulting json doc content:

{"My array of structures":[{"realVal":0.0,"intVal":0},{"realVal":1.0,"intVal":1},{"realVal":2.0,"intVal":2},{"realVal":3.0,"intVal":3}]}

And here is the data type definition:

TYPE ST_MyDataType :
STRUCT
    realVal : REAL;
    intVal  : INT;
END_STRUCT
END_TYPE

Edit: I did try to use only FB_JsonDomParser but I didn't manage to add Base64Object, it always ended up looking weird. I could add normal objects to array (int, bool, etc...), but when calling FB_JsonDomParser.PushbackBase64Value(jsonSetArrayObject, ADR(stTest), SIZEOF(stTest)); my result would end up looking like this: You can clearly see adding booleans works, but adding base 64 as a stand alone member or to be pushed to the array did not work - as mentioned, no experience on this subject, perhaps someone else can give some more valuable input.